| @c Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, |
| @c 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 |
| @c Free Software Foundation, Inc. |
| @c This is part of the GCC manual. |
| @c For copying conditions, see the file gcc.texi. |
| |
| @ignore |
| @c man begin INCLUDE |
| @include gcc-vers.texi |
| @c man end |
| |
| @c man begin COPYRIGHT |
| Copyright @copyright{} 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998, |
| 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, |
| 2012 |
| Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``GNU General Public License'' and ``Funding |
| Free Software'', the Front-Cover texts being (a) (see below), and with |
| the Back-Cover Texts being (b) (see below). A copy of the license is |
| included in the gfdl(7) man page. |
| |
| (a) The FSF's Front-Cover Text is: |
| |
| A GNU Manual |
| |
| (b) The FSF's Back-Cover Text is: |
| |
| You have freedom to copy and modify this GNU Manual, like GNU |
| software. Copies published by the Free Software Foundation raise |
| funds for GNU development. |
| @c man end |
| @c Set file name and title for the man page. |
| @setfilename gcc |
| @settitle GNU project C and C++ compiler |
| @c man begin SYNOPSIS |
| gcc [@option{-c}|@option{-S}|@option{-E}] [@option{-std=}@var{standard}] |
| [@option{-g}] [@option{-pg}] [@option{-O}@var{level}] |
| [@option{-W}@var{warn}@dots{}] [@option{-Wpedantic}] |
| [@option{-I}@var{dir}@dots{}] [@option{-L}@var{dir}@dots{}] |
| [@option{-D}@var{macro}[=@var{defn}]@dots{}] [@option{-U}@var{macro}] |
| [@option{-f}@var{option}@dots{}] [@option{-m}@var{machine-option}@dots{}] |
| [@option{-o} @var{outfile}] [@@@var{file}] @var{infile}@dots{} |
| |
| Only the most useful options are listed here; see below for the |
| remainder. @samp{g++} accepts mostly the same options as @samp{gcc}. |
| @c man end |
| @c man begin SEEALSO |
| gpl(7), gfdl(7), fsf-funding(7), |
| cpp(1), gcov(1), as(1), ld(1), gdb(1), adb(1), dbx(1), sdb(1) |
| and the Info entries for @file{gcc}, @file{cpp}, @file{as}, |
| @file{ld}, @file{binutils} and @file{gdb}. |
| @c man end |
| @c man begin BUGS |
| For instructions on reporting bugs, see |
| @w{@value{BUGURL}}. |
| @c man end |
| @c man begin AUTHOR |
| See the Info entry for @command{gcc}, or |
| @w{@uref{http://gcc.gnu.org/onlinedocs/gcc/Contributors.html}}, |
| for contributors to GCC@. |
| @c man end |
| @end ignore |
| |
| @node Invoking GCC |
| @chapter GCC Command Options |
| @cindex GCC command options |
| @cindex command options |
| @cindex options, GCC command |
| |
| @c man begin DESCRIPTION |
| When you invoke GCC, it normally does preprocessing, compilation, |
| assembly and linking. The ``overall options'' allow you to stop this |
| process at an intermediate stage. For example, the @option{-c} option |
| says not to run the linker. Then the output consists of object files |
| output by the assembler. |
| |
| Other options are passed on to one stage of processing. Some options |
| control the preprocessor and others the compiler itself. Yet other |
| options control the assembler and linker; most of these are not |
| documented here, since you rarely need to use any of them. |
| |
| @cindex C compilation options |
| Most of the command-line options that you can use with GCC are useful |
| for C programs; when an option is only useful with another language |
| (usually C++), the explanation says so explicitly. If the description |
| for a particular option does not mention a source language, you can use |
| that option with all supported languages. |
| |
| @cindex C++ compilation options |
| @xref{Invoking G++,,Compiling C++ Programs}, for a summary of special |
| options for compiling C++ programs. |
| |
| @cindex grouping options |
| @cindex options, grouping |
| The @command{gcc} program accepts options and file names as operands. Many |
| options have multi-letter names; therefore multiple single-letter options |
| may @emph{not} be grouped: @option{-dv} is very different from @w{@samp{-d |
| -v}}. |
| |
| @cindex order of options |
| @cindex options, order |
| You can mix options and other arguments. For the most part, the order |
| you use doesn't matter. Order does matter when you use several |
| options of the same kind; for example, if you specify @option{-L} more |
| than once, the directories are searched in the order specified. Also, |
| the placement of the @option{-l} option is significant. |
| |
| Many options have long names starting with @samp{-f} or with |
| @samp{-W}---for example, |
| @option{-fmove-loop-invariants}, @option{-Wformat} and so on. Most of |
| these have both positive and negative forms; the negative form of |
| @option{-ffoo} is @option{-fno-foo}. This manual documents |
| only one of these two forms, whichever one is not the default. |
| |
| @c man end |
| |
| @xref{Option Index}, for an index to GCC's options. |
| |
| @menu |
| * Option Summary:: Brief list of all options, without explanations. |
| * Overall Options:: Controlling the kind of output: |
| an executable, object files, assembler files, |
| or preprocessed source. |
| * Invoking G++:: Compiling C++ programs. |
| * C Dialect Options:: Controlling the variant of C language compiled. |
| * C++ Dialect Options:: Variations on C++. |
| * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C |
| and Objective-C++. |
| * Language Independent Options:: Controlling how diagnostics should be |
| formatted. |
| * Warning Options:: How picky should the compiler be? |
| * Debugging Options:: Symbol tables, measurements, and debugging dumps. |
| * Optimize Options:: How much optimization? |
| * Preprocessor Options:: Controlling header files and macro definitions. |
| Also, getting dependency information for Make. |
| * Assembler Options:: Passing options to the assembler. |
| * Link Options:: Specifying libraries and so on. |
| * Directory Options:: Where to find header files and libraries. |
| Where to find the compiler executable files. |
| * Spec Files:: How to pass switches to sub-processes. |
| * Target Options:: Running a cross-compiler, or an old version of GCC. |
| * Submodel Options:: Specifying minor hardware or convention variations, |
| such as 68010 vs 68020. |
| * Code Gen Options:: Specifying conventions for function calls, data layout |
| and register usage. |
| * Environment Variables:: Env vars that affect GCC. |
| * Precompiled Headers:: Compiling a header once, and using it many times. |
| @end menu |
| |
| @c man begin OPTIONS |
| |
| @node Option Summary |
| @section Option Summary |
| |
| Here is a summary of all the options, grouped by type. Explanations are |
| in the following sections. |
| |
| @table @emph |
| @item Overall Options |
| @xref{Overall Options,,Options Controlling the Kind of Output}. |
| @gccoptlist{-c -S -E -o @var{file} -no-canonical-prefixes @gol |
| -pipe -pass-exit-codes @gol |
| -x @var{language} -v -### --help@r{[}=@var{class}@r{[},@dots{}@r{]]} --target-help @gol |
| --version -wrapper @@@var{file} -fplugin=@var{file} -fplugin-arg-@var{name}=@var{arg} @gol |
| -fdump-ada-spec@r{[}-slim@r{]} -fada-spec-parent=@var{arg} -fdump-go-spec=@var{file}} |
| |
| @item C Language Options |
| @xref{C Dialect Options,,Options Controlling C Dialect}. |
| @gccoptlist{-ansi -std=@var{standard} -fgnu89-inline @gol |
| -aux-info @var{filename} -fallow-parameterless-variadic-functions @gol |
| -fno-asm -fno-builtin -fno-builtin-@var{function} @gol |
| -fhosted -ffreestanding -fopenmp -fms-extensions -fplan9-extensions @gol |
| -trigraphs -traditional -traditional-cpp @gol |
| -fallow-single-precision -fcond-mismatch -flax-vector-conversions @gol |
| -fsigned-bitfields -fsigned-char @gol |
| -funsigned-bitfields -funsigned-char} |
| |
| @item C++ Language Options |
| @xref{C++ Dialect Options,,Options Controlling C++ Dialect}. |
| @gccoptlist{-fabi-version=@var{n} -fno-access-control -fcheck-new @gol |
| -fconstexpr-depth=@var{n} -ffriend-injection @gol |
| -fno-elide-constructors @gol |
| -fno-enforce-eh-specs @gol |
| -ffor-scope -fno-for-scope -fno-gnu-keywords @gol |
| -fno-implicit-templates @gol |
| -fno-implicit-inline-templates @gol |
| -fno-implement-inlines -fms-extensions @gol |
| -fno-nonansi-builtins -fnothrow-opt -fno-operator-names @gol |
| -fno-optional-diags -fpermissive @gol |
| -fno-pretty-templates @gol |
| -frepo -fno-rtti -fstats -ftemplate-backtrace-limit=@var{n} @gol |
| -ftemplate-depth=@var{n} @gol |
| -fno-threadsafe-statics -fuse-cxa-atexit -fno-weak -nostdinc++ @gol |
| -fno-default-inline -fvisibility-inlines-hidden @gol |
| -fvisibility-ms-compat @gol |
| -Wabi -Wconversion-null -Wctor-dtor-privacy @gol |
| -Wdelete-non-virtual-dtor -Wliteral-suffix -Wnarrowing @gol |
| -Wnoexcept -Wnon-virtual-dtor -Wreorder @gol |
| -Weffc++ -Wstrict-null-sentinel @gol |
| -Wno-non-template-friend -Wold-style-cast @gol |
| -Woverloaded-virtual -Wno-pmf-conversions @gol |
| -Wsign-promo} |
| |
| @item Objective-C and Objective-C++ Language Options |
| @xref{Objective-C and Objective-C++ Dialect Options,,Options Controlling |
| Objective-C and Objective-C++ Dialects}. |
| @gccoptlist{-fconstant-string-class=@var{class-name} @gol |
| -fgnu-runtime -fnext-runtime @gol |
| -fno-nil-receivers @gol |
| -fobjc-abi-version=@var{n} @gol |
| -fobjc-call-cxx-cdtors @gol |
| -fobjc-direct-dispatch @gol |
| -fobjc-exceptions @gol |
| -fobjc-gc @gol |
| -fobjc-nilcheck @gol |
| -fobjc-std=objc1 @gol |
| -freplace-objc-classes @gol |
| -fzero-link @gol |
| -gen-decls @gol |
| -Wassign-intercept @gol |
| -Wno-protocol -Wselector @gol |
| -Wstrict-selector-match @gol |
| -Wundeclared-selector} |
| |
| @item Language Independent Options |
| @xref{Language Independent Options,,Options to Control Diagnostic Messages Formatting}. |
| @gccoptlist{-fmessage-length=@var{n} @gol |
| -fdiagnostics-show-location=@r{[}once@r{|}every-line@r{]} @gol |
| -fno-diagnostics-show-option -fno-diagnostics-show-caret} |
| |
| @item Warning Options |
| @xref{Warning Options,,Options to Request or Suppress Warnings}. |
| @gccoptlist{-fsyntax-only -fmax-errors=@var{n} -Wpedantic @gol |
| -pedantic-errors @gol |
| -w -Wextra -Wall -Waddress -Waggregate-return -Warray-bounds @gol |
| -Wno-attributes -Wno-builtin-macro-redefined @gol |
| -Wc++-compat -Wc++11-compat -Wcast-align -Wcast-qual @gol |
| -Wchar-subscripts -Wclobbered -Wcomment @gol |
| -Wconversion -Wcoverage-mismatch -Wno-cpp -Wno-deprecated @gol |
| -Wno-deprecated-declarations -Wdisabled-optimization @gol |
| -Wno-div-by-zero -Wdouble-promotion -Wempty-body -Wenum-compare @gol |
| -Wno-endif-labels -Werror -Werror=* @gol |
| -Wfatal-errors -Wfloat-equal -Wformat -Wformat=2 @gol |
| -Wno-format-contains-nul -Wno-format-extra-args -Wformat-nonliteral @gol |
| -Wformat-security -Wformat-y2k @gol |
| -Wframe-larger-than=@var{len} -Wno-free-nonheap-object -Wjump-misses-init @gol |
| -Wignored-qualifiers @gol |
| -Wimplicit -Wimplicit-function-declaration -Wimplicit-int @gol |
| -Winit-self -Winline -Wmaybe-uninitialized @gol |
| -Wno-int-to-pointer-cast -Wno-invalid-offsetof @gol |
| -Winvalid-pch -Wlarger-than=@var{len} -Wunsafe-loop-optimizations @gol |
| -Wlogical-op -Wlong-long @gol |
| -Wmain -Wmaybe-uninitialized -Wmissing-braces -Wmissing-field-initializers @gol |
| -Wmissing-include-dirs @gol |
| -Wno-mudflap @gol |
| -Wno-multichar -Wnonnull -Wno-overflow @gol |
| -Woverlength-strings -Wpacked -Wpacked-bitfield-compat -Wpadded @gol |
| -Wparentheses -Wpedantic-ms-format -Wno-pedantic-ms-format @gol |
| -Wpointer-arith -Wno-pointer-to-int-cast @gol |
| -Wredundant-decls @gol |
| -Wreturn-type -Wsequence-point -Wshadow @gol |
| -Wsign-compare -Wsign-conversion -Wsizeof-pointer-memaccess @gol |
| -Wstack-protector -Wstack-usage=@var{len} -Wstrict-aliasing @gol |
| -Wstrict-aliasing=n @gol -Wstrict-overflow -Wstrict-overflow=@var{n} @gol |
| -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} @gol |
| -Wmissing-format-attribute @gol |
| -Wswitch -Wswitch-default -Wswitch-enum -Wsync-nand @gol |
| -Wsystem-headers -Wtrampolines -Wtrigraphs -Wtype-limits -Wundef @gol |
| -Wuninitialized -Wunknown-pragmas -Wno-pragmas @gol |
| -Wunsuffixed-float-constants -Wunused -Wunused-function @gol |
| -Wunused-label -Wunused-local-typedefs -Wunused-parameter @gol |
| -Wno-unused-result -Wunused-value @gol -Wunused-variable @gol |
| -Wunused-but-set-parameter -Wunused-but-set-variable @gol |
| -Wuseless-cast -Wvariadic-macros -Wvector-operation-performance @gol |
| -Wvla -Wvolatile-register-var -Wwrite-strings -Wzero-as-null-pointer-constant} |
| |
| @item C and Objective-C-only Warning Options |
| @gccoptlist{-Wbad-function-cast -Wmissing-declarations @gol |
| -Wmissing-parameter-type -Wmissing-prototypes -Wnested-externs @gol |
| -Wold-style-declaration -Wold-style-definition @gol |
| -Wstrict-prototypes -Wtraditional -Wtraditional-conversion @gol |
| -Wdeclaration-after-statement -Wpointer-sign} |
| |
| @item Debugging Options |
| @xref{Debugging Options,,Options for Debugging Your Program or GCC}. |
| @gccoptlist{-d@var{letters} -dumpspecs -dumpmachine -dumpversion @gol |
| -fdbg-cnt-list -fdbg-cnt=@var{counter-value-list} @gol |
| -fdisable-ipa-@var{pass_name} @gol |
| -fdisable-rtl-@var{pass_name} @gol |
| -fdisable-rtl-@var{pass-name}=@var{range-list} @gol |
| -fdisable-tree-@var{pass_name} @gol |
| -fdisable-tree-@var{pass-name}=@var{range-list} @gol |
| -fdump-noaddr -fdump-unnumbered -fdump-unnumbered-links @gol |
| -fdump-translation-unit@r{[}-@var{n}@r{]} @gol |
| -fdump-class-hierarchy@r{[}-@var{n}@r{]} @gol |
| -fdump-ipa-all -fdump-ipa-cgraph -fdump-ipa-inline @gol |
| -fdump-passes @gol |
| -fdump-statistics @gol |
| -fdump-tree-all @gol |
| -fdump-tree-original@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-optimized@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-cfg -fdump-tree-vcg -fdump-tree-alias @gol |
| -fdump-tree-ch @gol |
| -fdump-tree-ssa@r{[}-@var{n}@r{]} -fdump-tree-pre@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-ccp@r{[}-@var{n}@r{]} -fdump-tree-dce@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-gimple@r{[}-raw@r{]} -fdump-tree-mudflap@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-dom@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-dse@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-phiprop@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-phiopt@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-copyrename@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-nrv -fdump-tree-vect @gol |
| -fdump-tree-sink @gol |
| -fdump-tree-sra@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-forwprop@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-fre@r{[}-@var{n}@r{]} @gol |
| -fdump-tree-vrp@r{[}-@var{n}@r{]} @gol |
| -ftree-vectorizer-verbose=@var{n} @gol |
| -fdump-tree-storeccp@r{[}-@var{n}@r{]} @gol |
| -fdump-final-insns=@var{file} @gol |
| -fcompare-debug@r{[}=@var{opts}@r{]} -fcompare-debug-second @gol |
| -feliminate-dwarf2-dups -fno-eliminate-unused-debug-types @gol |
| -feliminate-unused-debug-symbols -femit-class-debug-always @gol |
| -fenable-@var{kind}-@var{pass} @gol |
| -fenable-@var{kind}-@var{pass}=@var{range-list} @gol |
| -fdebug-types-section -fmem-report-wpa @gol |
| -fmem-report -fpre-ipa-mem-report -fpost-ipa-mem-report -fprofile-arcs @gol |
| -frandom-seed=@var{string} -fsched-verbose=@var{n} @gol |
| -fsel-sched-verbose -fsel-sched-dump-cfg -fsel-sched-pipelining-verbose @gol |
| -fstack-usage -ftest-coverage -ftime-report -fvar-tracking @gol |
| -fvar-tracking-assignments -fvar-tracking-assignments-toggle @gol |
| -g -g@var{level} -gtoggle -gcoff -gdwarf-@var{version} @gol |
| -ggdb -grecord-gcc-switches -gno-record-gcc-switches @gol |
| -gstabs -gstabs+ -gstrict-dwarf -gno-strict-dwarf @gol |
| -gvms -gxcoff -gxcoff+ @gol |
| -fno-merge-debug-strings -fno-dwarf2-cfi-asm @gol |
| -fdebug-prefix-map=@var{old}=@var{new} @gol |
| -femit-struct-debug-baseonly -femit-struct-debug-reduced @gol |
| -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} @gol |
| -p -pg -print-file-name=@var{library} -print-libgcc-file-name @gol |
| -print-multi-directory -print-multi-lib -print-multi-os-directory @gol |
| -print-prog-name=@var{program} -print-search-dirs -Q @gol |
| -print-sysroot -print-sysroot-headers-suffix @gol |
| -save-temps -save-temps=cwd -save-temps=obj -time@r{[}=@var{file}@r{]}} |
| |
| @item Optimization Options |
| @xref{Optimize Options,,Options that Control Optimization}. |
| @gccoptlist{-falign-functions[=@var{n}] -falign-jumps[=@var{n}] @gol |
| -falign-labels[=@var{n}] -falign-loops[=@var{n}] -fassociative-math @gol |
| -fauto-inc-dec -fbranch-probabilities -fbranch-target-load-optimize @gol |
| -fbranch-target-load-optimize2 -fbtr-bb-exclusive -fcaller-saves @gol |
| -fcheck-data-deps -fcombine-stack-adjustments -fconserve-stack @gol |
| -fcompare-elim -fcprop-registers -fcrossjumping @gol |
| -fcse-follow-jumps -fcse-skip-blocks -fcx-fortran-rules @gol |
| -fcx-limited-range @gol |
| -fdata-sections -fdce -fdelayed-branch @gol |
| -fdelete-null-pointer-checks -fdevirtualize -fdse @gol |
| -fearly-inlining -fipa-sra -fexpensive-optimizations -ffat-lto-objects @gol |
| -ffast-math -ffinite-math-only -ffloat-store -fexcess-precision=@var{style} @gol |
| -fforward-propagate -ffp-contract=@var{style} -ffunction-sections @gol |
| -fgcse -fgcse-after-reload -fgcse-las -fgcse-lm -fgraphite-identity @gol |
| -fgcse-sm -fhoist-adjacent-loads -fif-conversion @gol |
| -fif-conversion2 -findirect-inlining @gol |
| -finline-functions -finline-functions-called-once -finline-limit=@var{n} @gol |
| -finline-small-functions -fipa-cp -fipa-cp-clone @gol |
| -fipa-pta -fipa-profile -fipa-pure-const -fipa-reference @gol |
| -fira-algorithm=@var{algorithm} @gol |
| -fira-region=@var{region} @gol |
| -fira-loop-pressure -fno-ira-share-save-slots @gol |
| -fno-ira-share-spill-slots -fira-verbose=@var{n} @gol |
| -fivopts -fkeep-inline-functions -fkeep-static-consts @gol |
| -floop-block -floop-interchange -floop-strip-mine -floop-nest-optimize @gol |
| -floop-parallelize-all -flto -flto-compression-level @gol |
| -flto-partition=@var{alg} -flto-report -fmerge-all-constants @gol |
| -fmerge-constants -fmodulo-sched -fmodulo-sched-allow-regmoves @gol |
| -fmove-loop-invariants fmudflap -fmudflapir -fmudflapth -fno-branch-count-reg @gol |
| -fno-default-inline @gol |
| -fno-defer-pop -fno-function-cse -fno-guess-branch-probability @gol |
| -fno-inline -fno-math-errno -fno-peephole -fno-peephole2 @gol |
| -fno-sched-interblock -fno-sched-spec -fno-signed-zeros @gol |
| -fno-toplevel-reorder -fno-trapping-math -fno-zero-initialized-in-bss @gol |
| -fomit-frame-pointer -foptimize-register-move -foptimize-sibling-calls @gol |
| -fpartial-inlining -fpeel-loops -fpredictive-commoning @gol |
| -fprefetch-loop-arrays @gol |
| -fprofile-correction -fprofile-dir=@var{path} -fprofile-generate @gol |
| -fprofile-generate=@var{path} @gol |
| -fprofile-use -fprofile-use=@var{path} -fprofile-values @gol |
| -freciprocal-math -free -fregmove -frename-registers -freorder-blocks @gol |
| -freorder-blocks-and-partition -freorder-functions @gol |
| -frerun-cse-after-loop -freschedule-modulo-scheduled-loops @gol |
| -frounding-math -fsched2-use-superblocks -fsched-pressure @gol |
| -fsched-spec-load -fsched-spec-load-dangerous @gol |
| -fsched-stalled-insns-dep[=@var{n}] -fsched-stalled-insns[=@var{n}] @gol |
| -fsched-group-heuristic -fsched-critical-path-heuristic @gol |
| -fsched-spec-insn-heuristic -fsched-rank-heuristic @gol |
| -fsched-last-insn-heuristic -fsched-dep-count-heuristic @gol |
| -fschedule-insns -fschedule-insns2 -fsection-anchors @gol |
| -fselective-scheduling -fselective-scheduling2 @gol |
| -fsel-sched-pipelining -fsel-sched-pipelining-outer-loops @gol |
| -fshrink-wrap -fsignaling-nans -fsingle-precision-constant @gol |
| -fsplit-ivs-in-unroller -fsplit-wide-types -fstack-protector @gol |
| -fstack-protector-all -fstrict-aliasing -fstrict-overflow @gol |
| -fthread-jumps -ftracer -ftree-bit-ccp @gol |
| -ftree-builtin-call-dce -ftree-ccp -ftree-ch @gol |
| -ftree-coalesce-inline-vars -ftree-coalesce-vars -ftree-copy-prop @gol |
| -ftree-copyrename -ftree-dce -ftree-dominator-opts -ftree-dse @gol |
| -ftree-forwprop -ftree-fre -ftree-loop-if-convert @gol |
| -ftree-loop-if-convert-stores -ftree-loop-im @gol |
| -ftree-phiprop -ftree-loop-distribution -ftree-loop-distribute-patterns @gol |
| -ftree-loop-ivcanon -ftree-loop-linear -ftree-loop-optimize @gol |
| -ftree-parallelize-loops=@var{n} -ftree-pre -ftree-partial-pre -ftree-pta @gol |
| -ftree-reassoc -ftree-sink -ftree-slsr -ftree-sra @gol |
| -ftree-switch-conversion -ftree-tail-merge @gol |
| -ftree-ter -ftree-vect-loop-version -ftree-vectorize -ftree-vrp @gol |
| -funit-at-a-time -funroll-all-loops -funroll-loops @gol |
| -funsafe-loop-optimizations -funsafe-math-optimizations -funswitch-loops @gol |
| -fvariable-expansion-in-unroller -fvect-cost-model -fvpt -fweb @gol |
| -fwhole-program -fwpa -fuse-linker-plugin @gol |
| --param @var{name}=@var{value} |
| -O -O0 -O1 -O2 -O3 -Os -Ofast -Og} |
| |
| @item Preprocessor Options |
| @xref{Preprocessor Options,,Options Controlling the Preprocessor}. |
| @gccoptlist{-A@var{question}=@var{answer} @gol |
| -A-@var{question}@r{[}=@var{answer}@r{]} @gol |
| -C -dD -dI -dM -dN @gol |
| -D@var{macro}@r{[}=@var{defn}@r{]} -E -H @gol |
| -idirafter @var{dir} @gol |
| -include @var{file} -imacros @var{file} @gol |
| -iprefix @var{file} -iwithprefix @var{dir} @gol |
| -iwithprefixbefore @var{dir} -isystem @var{dir} @gol |
| -imultilib @var{dir} -isysroot @var{dir} @gol |
| -M -MM -MF -MG -MP -MQ -MT -nostdinc @gol |
| -P -fdebug-cpp -ftrack-macro-expansion -fworking-directory @gol |
| -remap -trigraphs -undef -U@var{macro} @gol |
| -Wp,@var{option} -Xpreprocessor @var{option} -no-integrated-cpp} |
| |
| @item Assembler Option |
| @xref{Assembler Options,,Passing Options to the Assembler}. |
| @gccoptlist{-Wa,@var{option} -Xassembler @var{option}} |
| |
| @item Linker Options |
| @xref{Link Options,,Options for Linking}. |
| @gccoptlist{@var{object-file-name} -l@var{library} @gol |
| -nostartfiles -nodefaultlibs -nostdlib -pie -rdynamic @gol |
| -s -static -static-libgcc -static-libstdc++ -shared @gol |
| -shared-libgcc -symbolic @gol |
| -T @var{script} -Wl,@var{option} -Xlinker @var{option} @gol |
| -u @var{symbol}} |
| |
| @item Directory Options |
| @xref{Directory Options,,Options for Directory Search}. |
| @gccoptlist{-B@var{prefix} -I@var{dir} -iplugindir=@var{dir} @gol |
| -iquote@var{dir} -L@var{dir} -specs=@var{file} -I- @gol |
| --sysroot=@var{dir} --no-sysroot-suffix} |
| |
| @item Machine Dependent Options |
| @xref{Submodel Options,,Hardware Models and Configurations}. |
| @c This list is ordered alphanumerically by subsection name. |
| @c Try and put the significant identifier (CPU or system) first, |
| @c so users have a clue at guessing where the ones they want will be. |
| |
| @emph{AArch64 Options} |
| @gccoptlist{-mbig-endian -mlittle-endian @gol |
| -mgeneral-regs-only @gol |
| -mcmodel=tiny -mcmodel=small -mcmodel=large @gol |
| -mstrict-align @gol |
| -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol |
| -mtls-dialect=desc -mtls-dialect=traditional @gol |
| -march=@var{name} -mcpu=@var{name} -mtune=@var{name}} |
| |
| @emph{Adapteva Epiphany Options} |
| @gccoptlist{-mhalf-reg-file -mprefer-short-insn-regs @gol |
| -mbranch-cost=@var{num} -mcmove -mnops=@var{num} -msoft-cmpsf @gol |
| -msplit-lohi -mpost-inc -mpost-modify -mstack-offset=@var{num} @gol |
| -mround-nearest -mlong-calls -mshort-calls -msmall16 @gol |
| -mfp-mode=@var{mode} -mvect-double -max-vect-align=@var{num} @gol |
| -msplit-vecmove-early -m1reg-@var{reg}} |
| |
| @emph{ARM Options} |
| @gccoptlist{-mapcs-frame -mno-apcs-frame @gol |
| -mabi=@var{name} @gol |
| -mapcs-stack-check -mno-apcs-stack-check @gol |
| -mapcs-float -mno-apcs-float @gol |
| -mapcs-reentrant -mno-apcs-reentrant @gol |
| -msched-prolog -mno-sched-prolog @gol |
| -mlittle-endian -mbig-endian -mwords-little-endian @gol |
| -mfloat-abi=@var{name} @gol |
| -mfp16-format=@var{name} |
| -mthumb-interwork -mno-thumb-interwork @gol |
| -mcpu=@var{name} -march=@var{name} -mfpu=@var{name} @gol |
| -mstructure-size-boundary=@var{n} @gol |
| -mabort-on-noreturn @gol |
| -mlong-calls -mno-long-calls @gol |
| -msingle-pic-base -mno-single-pic-base @gol |
| -mpic-register=@var{reg} @gol |
| -mnop-fun-dllimport @gol |
| -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns @gol |
| -mpoke-function-name @gol |
| -mthumb -marm @gol |
| -mtpcs-frame -mtpcs-leaf-frame @gol |
| -mcaller-super-interworking -mcallee-super-interworking @gol |
| -mtp=@var{name} -mtls-dialect=@var{dialect} @gol |
| -mword-relocations @gol |
| -mfix-cortex-m3-ldrd @gol |
| -munaligned-access} |
| |
| @emph{AVR Options} |
| @gccoptlist{-mmcu=@var{mcu} -maccumulate-args -mbranch-cost=@var{cost} @gol |
| -mcall-prologues -mint8 -mno-interrupts -mrelax -mshort-calls @gol |
| -mstrict-X -mtiny-stack} |
| |
| @emph{Blackfin Options} |
| @gccoptlist{-mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} @gol |
| -msim -momit-leaf-frame-pointer -mno-omit-leaf-frame-pointer @gol |
| -mspecld-anomaly -mno-specld-anomaly -mcsync-anomaly -mno-csync-anomaly @gol |
| -mlow-64k -mno-low64k -mstack-check-l1 -mid-shared-library @gol |
| -mno-id-shared-library -mshared-library-id=@var{n} @gol |
| -mleaf-id-shared-library -mno-leaf-id-shared-library @gol |
| -msep-data -mno-sep-data -mlong-calls -mno-long-calls @gol |
| -mfast-fp -minline-plt -mmulticore -mcorea -mcoreb -msdram @gol |
| -micplb} |
| |
| @emph{C6X Options} |
| @gccoptlist{-mbig-endian -mlittle-endian -march=@var{cpu} @gol |
| -msim -msdata=@var{sdata-type}} |
| |
| @emph{CRIS Options} |
| @gccoptlist{-mcpu=@var{cpu} -march=@var{cpu} -mtune=@var{cpu} @gol |
| -mmax-stack-frame=@var{n} -melinux-stacksize=@var{n} @gol |
| -metrax4 -metrax100 -mpdebug -mcc-init -mno-side-effects @gol |
| -mstack-align -mdata-align -mconst-align @gol |
| -m32-bit -m16-bit -m8-bit -mno-prologue-epilogue -mno-gotplt @gol |
| -melf -maout -melinux -mlinux -sim -sim2 @gol |
| -mmul-bug-workaround -mno-mul-bug-workaround} |
| |
| @emph{CR16 Options} |
| @gccoptlist{-mmac @gol |
| -mcr16cplus -mcr16c @gol |
| -msim -mint32 -mbit-ops |
| -mdata-model=@var{model}} |
| |
| @emph{Darwin Options} |
| @gccoptlist{-all_load -allowable_client -arch -arch_errors_fatal @gol |
| -arch_only -bind_at_load -bundle -bundle_loader @gol |
| -client_name -compatibility_version -current_version @gol |
| -dead_strip @gol |
| -dependency-file -dylib_file -dylinker_install_name @gol |
| -dynamic -dynamiclib -exported_symbols_list @gol |
| -filelist -flat_namespace -force_cpusubtype_ALL @gol |
| -force_flat_namespace -headerpad_max_install_names @gol |
| -iframework @gol |
| -image_base -init -install_name -keep_private_externs @gol |
| -multi_module -multiply_defined -multiply_defined_unused @gol |
| -noall_load -no_dead_strip_inits_and_terms @gol |
| -nofixprebinding -nomultidefs -noprebind -noseglinkedit @gol |
| -pagezero_size -prebind -prebind_all_twolevel_modules @gol |
| -private_bundle -read_only_relocs -sectalign @gol |
| -sectobjectsymbols -whyload -seg1addr @gol |
| -sectcreate -sectobjectsymbols -sectorder @gol |
| -segaddr -segs_read_only_addr -segs_read_write_addr @gol |
| -seg_addr_table -seg_addr_table_filename -seglinkedit @gol |
| -segprot -segs_read_only_addr -segs_read_write_addr @gol |
| -single_module -static -sub_library -sub_umbrella @gol |
| -twolevel_namespace -umbrella -undefined @gol |
| -unexported_symbols_list -weak_reference_mismatches @gol |
| -whatsloaded -F -gused -gfull -mmacosx-version-min=@var{version} @gol |
| -mkernel -mone-byte-bool} |
| |
| @emph{DEC Alpha Options} |
| @gccoptlist{-mno-fp-regs -msoft-float @gol |
| -mieee -mieee-with-inexact -mieee-conformant @gol |
| -mfp-trap-mode=@var{mode} -mfp-rounding-mode=@var{mode} @gol |
| -mtrap-precision=@var{mode} -mbuild-constants @gol |
| -mcpu=@var{cpu-type} -mtune=@var{cpu-type} @gol |
| -mbwx -mmax -mfix -mcix @gol |
| -mfloat-vax -mfloat-ieee @gol |
| -mexplicit-relocs -msmall-data -mlarge-data @gol |
| -msmall-text -mlarge-text @gol |
| -mmemory-latency=@var{time}} |
| |
| @emph{FR30 Options} |
| @gccoptlist{-msmall-model -mno-lsim} |
| |
| @emph{FRV Options} |
| @gccoptlist{-mgpr-32 -mgpr-64 -mfpr-32 -mfpr-64 @gol |
| -mhard-float -msoft-float @gol |
| -malloc-cc -mfixed-cc -mdword -mno-dword @gol |
| -mdouble -mno-double @gol |
| -mmedia -mno-media -mmuladd -mno-muladd @gol |
| -mfdpic -minline-plt -mgprel-ro -multilib-library-pic @gol |
| -mlinked-fp -mlong-calls -malign-labels @gol |
| -mlibrary-pic -macc-4 -macc-8 @gol |
| -mpack -mno-pack -mno-eflags -mcond-move -mno-cond-move @gol |
| -moptimize-membar -mno-optimize-membar @gol |
| -mscc -mno-scc -mcond-exec -mno-cond-exec @gol |
| -mvliw-branch -mno-vliw-branch @gol |
| -mmulti-cond-exec -mno-multi-cond-exec -mnested-cond-exec @gol |
| -mno-nested-cond-exec -mtomcat-stats @gol |
| -mTLS -mtls @gol |
| -mcpu=@var{cpu}} |
| |
| @emph{GNU/Linux Options} |
| @gccoptlist{-mglibc -muclibc -mbionic -mandroid @gol |
| -tno-android-cc -tno-android-ld} |
| |
| @emph{H8/300 Options} |
| @gccoptlist{-mrelax -mh -ms -mn -mexr -mno-exr -mint32 -malign-300} |
| |
| @emph{HPPA Options} |
| @gccoptlist{-march=@var{architecture-type} @gol |
| -mbig-switch -mdisable-fpregs -mdisable-indexing @gol |
| -mfast-indirect-calls -mgas -mgnu-ld -mhp-ld @gol |
| -mfixed-range=@var{register-range} @gol |
| -mjump-in-delay -mlinker-opt -mlong-calls @gol |
| -mlong-load-store -mno-big-switch -mno-disable-fpregs @gol |
| -mno-disable-indexing -mno-fast-indirect-calls -mno-gas @gol |
| -mno-jump-in-delay -mno-long-load-store @gol |
| -mno-portable-runtime -mno-soft-float @gol |
| -mno-space-regs -msoft-float -mpa-risc-1-0 @gol |
| -mpa-risc-1-1 -mpa-risc-2-0 -mportable-runtime @gol |
| -mschedule=@var{cpu-type} -mspace-regs -msio -mwsio @gol |
| -munix=@var{unix-std} -nolibdld -static -threads} |
| |
| @emph{i386 and x86-64 Options} |
| @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol |
| -mfpmath=@var{unit} @gol |
| -masm=@var{dialect} -mno-fancy-math-387 @gol |
| -mno-fp-ret-in-387 -msoft-float @gol |
| -mno-wide-multiply -mrtd -malign-double @gol |
| -mpreferred-stack-boundary=@var{num} @gol |
| -mincoming-stack-boundary=@var{num} @gol |
| -mcld -mcx16 -msahf -mmovbe -mcrc32 @gol |
| -mrecip -mrecip=@var{opt} @gol |
| -mvzeroupper @gol |
| -mmmx -msse -msse2 -msse3 -mssse3 -msse4.1 -msse4.2 -msse4 -mavx @gol |
| -mavx2 -maes -mpclmul -mfsgsbase -mrdrnd -mf16c -mfma @gol |
| -msse4a -m3dnow -mpopcnt -mabm -mbmi -mtbm -mfma4 -mxop -mlzcnt @gol |
| -mbmi2 -mrtm -mlwp -mthreads @gol |
| -mno-align-stringops -minline-all-stringops @gol |
| -minline-stringops-dynamically -mstringop-strategy=@var{alg} @gol |
| -mpush-args -maccumulate-outgoing-args -m128bit-long-double @gol |
| -m96bit-long-double -mlong-double-64 -mlong-double-80 @gol |
| -mregparm=@var{num} -msseregparm @gol |
| -mveclibabi=@var{type} -mvect8-ret-in-mem @gol |
| -mpc32 -mpc64 -mpc80 -mstackrealign @gol |
| -momit-leaf-frame-pointer -mno-red-zone -mno-tls-direct-seg-refs @gol |
| -mcmodel=@var{code-model} -mabi=@var{name} -maddress-mode=@var{mode} @gol |
| -m32 -m64 -mx32 -mlarge-data-threshold=@var{num} @gol |
| -msse2avx -mfentry -m8bit-idiv @gol |
| -mavx256-split-unaligned-load -mavx256-split-unaligned-store} |
| |
| @emph{i386 and x86-64 Windows Options} |
| @gccoptlist{-mconsole -mcygwin -mno-cygwin -mdll @gol |
| -mnop-fun-dllimport -mthread @gol |
| -municode -mwin32 -mwindows -fno-set-stack-executable} |
| |
| @emph{IA-64 Options} |
| @gccoptlist{-mbig-endian -mlittle-endian -mgnu-as -mgnu-ld -mno-pic @gol |
| -mvolatile-asm-stop -mregister-names -msdata -mno-sdata @gol |
| -mconstant-gp -mauto-pic -mfused-madd @gol |
| -minline-float-divide-min-latency @gol |
| -minline-float-divide-max-throughput @gol |
| -mno-inline-float-divide @gol |
| -minline-int-divide-min-latency @gol |
| -minline-int-divide-max-throughput @gol |
| -mno-inline-int-divide @gol |
| -minline-sqrt-min-latency -minline-sqrt-max-throughput @gol |
| -mno-inline-sqrt @gol |
| -mdwarf2-asm -mearly-stop-bits @gol |
| -mfixed-range=@var{register-range} -mtls-size=@var{tls-size} @gol |
| -mtune=@var{cpu-type} -milp32 -mlp64 @gol |
| -msched-br-data-spec -msched-ar-data-spec -msched-control-spec @gol |
| -msched-br-in-data-spec -msched-ar-in-data-spec -msched-in-control-spec @gol |
| -msched-spec-ldc -msched-spec-control-ldc @gol |
| -msched-prefer-non-data-spec-insns -msched-prefer-non-control-spec-insns @gol |
| -msched-stop-bits-after-every-cycle -msched-count-spec-in-critical-path @gol |
| -msel-sched-dont-check-control-spec -msched-fp-mem-deps-zero-cost @gol |
| -msched-max-memory-insns-hard-limit -msched-max-memory-insns=@var{max-insns}} |
| |
| @emph{LM32 Options} |
| @gccoptlist{-mbarrel-shift-enabled -mdivide-enabled -mmultiply-enabled @gol |
| -msign-extend-enabled -muser-enabled} |
| |
| @emph{M32R/D Options} |
| @gccoptlist{-m32r2 -m32rx -m32r @gol |
| -mdebug @gol |
| -malign-loops -mno-align-loops @gol |
| -missue-rate=@var{number} @gol |
| -mbranch-cost=@var{number} @gol |
| -mmodel=@var{code-size-model-type} @gol |
| -msdata=@var{sdata-type} @gol |
| -mno-flush-func -mflush-func=@var{name} @gol |
| -mno-flush-trap -mflush-trap=@var{number} @gol |
| -G @var{num}} |
| |
| @emph{M32C Options} |
| @gccoptlist{-mcpu=@var{cpu} -msim -memregs=@var{number}} |
| |
| @emph{M680x0 Options} |
| @gccoptlist{-march=@var{arch} -mcpu=@var{cpu} -mtune=@var{tune} |
| -m68000 -m68020 -m68020-40 -m68020-60 -m68030 -m68040 @gol |
| -m68060 -mcpu32 -m5200 -m5206e -m528x -m5307 -m5407 @gol |
| -mcfv4e -mbitfield -mno-bitfield -mc68000 -mc68020 @gol |
| -mnobitfield -mrtd -mno-rtd -mdiv -mno-div -mshort @gol |
| -mno-short -mhard-float -m68881 -msoft-float -mpcrel @gol |
| -malign-int -mstrict-align -msep-data -mno-sep-data @gol |
| -mshared-library-id=n -mid-shared-library -mno-id-shared-library @gol |
| -mxgot -mno-xgot} |
| |
| @emph{MCore Options} |
| @gccoptlist{-mhardlit -mno-hardlit -mdiv -mno-div -mrelax-immediates @gol |
| -mno-relax-immediates -mwide-bitfields -mno-wide-bitfields @gol |
| -m4byte-functions -mno-4byte-functions -mcallgraph-data @gol |
| -mno-callgraph-data -mslow-bytes -mno-slow-bytes -mno-lsim @gol |
| -mlittle-endian -mbig-endian -m210 -m340 -mstack-increment} |
| |
| @emph{MeP Options} |
| @gccoptlist{-mabsdiff -mall-opts -maverage -mbased=@var{n} -mbitops @gol |
| -mc=@var{n} -mclip -mconfig=@var{name} -mcop -mcop32 -mcop64 -mivc2 @gol |
| -mdc -mdiv -meb -mel -mio-volatile -ml -mleadz -mm -mminmax @gol |
| -mmult -mno-opts -mrepeat -ms -msatur -msdram -msim -msimnovec -mtf @gol |
| -mtiny=@var{n}} |
| |
| @emph{MicroBlaze Options} |
| @gccoptlist{-msoft-float -mhard-float -msmall-divides -mcpu=@var{cpu} @gol |
| -mmemcpy -mxl-soft-mul -mxl-soft-div -mxl-barrel-shift @gol |
| -mxl-pattern-compare -mxl-stack-check -mxl-gp-opt -mno-clearbss @gol |
| -mxl-multiply-high -mxl-float-convert -mxl-float-sqrt @gol |
| -mxl-mode-@var{app-model}} |
| |
| @emph{MIPS Options} |
| @gccoptlist{-EL -EB -march=@var{arch} -mtune=@var{arch} @gol |
| -mips1 -mips2 -mips3 -mips4 -mips32 -mips32r2 @gol |
| -mips64 -mips64r2 @gol |
| -mips16 -mno-mips16 -mflip-mips16 @gol |
| -minterlink-mips16 -mno-interlink-mips16 @gol |
| -mabi=@var{abi} -mabicalls -mno-abicalls @gol |
| -mshared -mno-shared -mplt -mno-plt -mxgot -mno-xgot @gol |
| -mgp32 -mgp64 -mfp32 -mfp64 -mhard-float -msoft-float @gol |
| -mno-float -msingle-float -mdouble-float @gol |
| -mdsp -mno-dsp -mdspr2 -mno-dspr2 @gol |
| -mmcu -mmno-mcu @gol |
| -mfpu=@var{fpu-type} @gol |
| -msmartmips -mno-smartmips @gol |
| -mpaired-single -mno-paired-single -mdmx -mno-mdmx @gol |
| -mips3d -mno-mips3d -mmt -mno-mt -mllsc -mno-llsc @gol |
| -mlong64 -mlong32 -msym32 -mno-sym32 @gol |
| -G@var{num} -mlocal-sdata -mno-local-sdata @gol |
| -mextern-sdata -mno-extern-sdata -mgpopt -mno-gopt @gol |
| -membedded-data -mno-embedded-data @gol |
| -muninit-const-in-rodata -mno-uninit-const-in-rodata @gol |
| -mcode-readable=@var{setting} @gol |
| -msplit-addresses -mno-split-addresses @gol |
| -mexplicit-relocs -mno-explicit-relocs @gol |
| -mcheck-zero-division -mno-check-zero-division @gol |
| -mdivide-traps -mdivide-breaks @gol |
| -mmemcpy -mno-memcpy -mlong-calls -mno-long-calls @gol |
| -mmad -mno-mad -mfused-madd -mno-fused-madd -nocpp @gol |
| -mfix-24k -mno-fix-24k @gol |
| -mfix-r4000 -mno-fix-r4000 -mfix-r4400 -mno-fix-r4400 @gol |
| -mfix-r10000 -mno-fix-r10000 -mfix-vr4120 -mno-fix-vr4120 @gol |
| -mfix-vr4130 -mno-fix-vr4130 -mfix-sb1 -mno-fix-sb1 @gol |
| -mflush-func=@var{func} -mno-flush-func @gol |
| -mbranch-cost=@var{num} -mbranch-likely -mno-branch-likely @gol |
| -mfp-exceptions -mno-fp-exceptions @gol |
| -mvr4130-align -mno-vr4130-align -msynci -mno-synci @gol |
| -mrelax-pic-calls -mno-relax-pic-calls -mmcount-ra-address} |
| |
| @emph{MMIX Options} |
| @gccoptlist{-mlibfuncs -mno-libfuncs -mepsilon -mno-epsilon -mabi=gnu @gol |
| -mabi=mmixware -mzero-extend -mknuthdiv -mtoplevel-symbols @gol |
| -melf -mbranch-predict -mno-branch-predict -mbase-addresses @gol |
| -mno-base-addresses -msingle-exit -mno-single-exit} |
| |
| @emph{MN10300 Options} |
| @gccoptlist{-mmult-bug -mno-mult-bug @gol |
| -mno-am33 -mam33 -mam33-2 -mam34 @gol |
| -mtune=@var{cpu-type} @gol |
| -mreturn-pointer-on-d0 @gol |
| -mno-crt0 -mrelax -mliw -msetlb} |
| |
| @emph{Moxie Options} |
| @gccoptlist{-meb -mel -mno-crt0} |
| |
| @emph{PDP-11 Options} |
| @gccoptlist{-mfpu -msoft-float -mac0 -mno-ac0 -m40 -m45 -m10 @gol |
| -mbcopy -mbcopy-builtin -mint32 -mno-int16 @gol |
| -mint16 -mno-int32 -mfloat32 -mno-float64 @gol |
| -mfloat64 -mno-float32 -mabshi -mno-abshi @gol |
| -mbranch-expensive -mbranch-cheap @gol |
| -munix-asm -mdec-asm} |
| |
| @emph{picoChip Options} |
| @gccoptlist{-mae=@var{ae_type} -mvliw-lookahead=@var{N} @gol |
| -msymbol-as-address -mno-inefficient-warnings} |
| |
| @emph{PowerPC Options} |
| See RS/6000 and PowerPC Options. |
| |
| @emph{RL78 Options} |
| @gccoptlist{-msim -mmul=none -mmul=g13 -mmul=rl78} |
| |
| @emph{RS/6000 and PowerPC Options} |
| @gccoptlist{-mcpu=@var{cpu-type} @gol |
| -mtune=@var{cpu-type} @gol |
| -mcmodel=@var{code-model} @gol |
| -mpowerpc64 @gol |
| -maltivec -mno-altivec @gol |
| -mpowerpc-gpopt -mno-powerpc-gpopt @gol |
| -mpowerpc-gfxopt -mno-powerpc-gfxopt @gol |
| -mmfcrf -mno-mfcrf -mpopcntb -mno-popcntb -mpopcntd -mno-popcntd @gol |
| -mfprnd -mno-fprnd @gol |
| -mcmpb -mno-cmpb -mmfpgpr -mno-mfpgpr -mhard-dfp -mno-hard-dfp @gol |
| -mfull-toc -mminimal-toc -mno-fp-in-toc -mno-sum-in-toc @gol |
| -m64 -m32 -mxl-compat -mno-xl-compat -mpe @gol |
| -malign-power -malign-natural @gol |
| -msoft-float -mhard-float -mmultiple -mno-multiple @gol |
| -msingle-float -mdouble-float -msimple-fpu @gol |
| -mstring -mno-string -mupdate -mno-update @gol |
| -mavoid-indexed-addresses -mno-avoid-indexed-addresses @gol |
| -mfused-madd -mno-fused-madd -mbit-align -mno-bit-align @gol |
| -mstrict-align -mno-strict-align -mrelocatable @gol |
| -mno-relocatable -mrelocatable-lib -mno-relocatable-lib @gol |
| -mtoc -mno-toc -mlittle -mlittle-endian -mbig -mbig-endian @gol |
| -mdynamic-no-pic -maltivec -mswdiv -msingle-pic-base @gol |
| -mprioritize-restricted-insns=@var{priority} @gol |
| -msched-costly-dep=@var{dependence_type} @gol |
| -minsert-sched-nops=@var{scheme} @gol |
| -mcall-sysv -mcall-netbsd @gol |
| -maix-struct-return -msvr4-struct-return @gol |
| -mabi=@var{abi-type} -msecure-plt -mbss-plt @gol |
| -mblock-move-inline-limit=@var{num} @gol |
| -misel -mno-isel @gol |
| -misel=yes -misel=no @gol |
| -mspe -mno-spe @gol |
| -mspe=yes -mspe=no @gol |
| -mpaired @gol |
| -mgen-cell-microcode -mwarn-cell-microcode @gol |
| -mvrsave -mno-vrsave @gol |
| -mmulhw -mno-mulhw @gol |
| -mdlmzb -mno-dlmzb @gol |
| -mfloat-gprs=yes -mfloat-gprs=no -mfloat-gprs=single -mfloat-gprs=double @gol |
| -mprototype -mno-prototype @gol |
| -msim -mmvme -mads -myellowknife -memb -msdata @gol |
| -msdata=@var{opt} -mvxworks -G @var{num} -pthread @gol |
| -mrecip -mrecip=@var{opt} -mno-recip -mrecip-precision @gol |
| -mno-recip-precision @gol |
| -mveclibabi=@var{type} -mfriz -mno-friz @gol |
| -mpointers-to-nested-functions -mno-pointers-to-nested-functions @gol |
| -msave-toc-indirect -mno-save-toc-indirect} |
| |
| @emph{RX Options} |
| @gccoptlist{-m64bit-doubles -m32bit-doubles -fpu -nofpu@gol |
| -mcpu=@gol |
| -mbig-endian-data -mlittle-endian-data @gol |
| -msmall-data @gol |
| -msim -mno-sim@gol |
| -mas100-syntax -mno-as100-syntax@gol |
| -mrelax@gol |
| -mmax-constant-size=@gol |
| -mint-register=@gol |
| -mpid@gol |
| -msave-acc-in-interrupts} |
| |
| @emph{S/390 and zSeries Options} |
| @gccoptlist{-mtune=@var{cpu-type} -march=@var{cpu-type} @gol |
| -mhard-float -msoft-float -mhard-dfp -mno-hard-dfp @gol |
| -mlong-double-64 -mlong-double-128 @gol |
| -mbackchain -mno-backchain -mpacked-stack -mno-packed-stack @gol |
| -msmall-exec -mno-small-exec -mmvcle -mno-mvcle @gol |
| -m64 -m31 -mdebug -mno-debug -mesa -mzarch @gol |
| -mtpf-trace -mno-tpf-trace -mfused-madd -mno-fused-madd @gol |
| -mwarn-framesize -mwarn-dynamicstack -mstack-size -mstack-guard} |
| |
| @emph{Score Options} |
| @gccoptlist{-meb -mel @gol |
| -mnhwloop @gol |
| -muls @gol |
| -mmac @gol |
| -mscore5 -mscore5u -mscore7 -mscore7d} |
| |
| @emph{SH Options} |
| @gccoptlist{-m1 -m2 -m2e @gol |
| -m2a-nofpu -m2a-single-only -m2a-single -m2a @gol |
| -m3 -m3e @gol |
| -m4-nofpu -m4-single-only -m4-single -m4 @gol |
| -m4a-nofpu -m4a-single-only -m4a-single -m4a -m4al @gol |
| -m5-64media -m5-64media-nofpu @gol |
| -m5-32media -m5-32media-nofpu @gol |
| -m5-compact -m5-compact-nofpu @gol |
| -mb -ml -mdalign -mrelax @gol |
| -mbigtable -mfmovd -mhitachi -mrenesas -mno-renesas -mnomacsave @gol |
| -mieee -mno-ieee -mbitops -misize -minline-ic_invalidate -mpadstruct @gol |
| -mspace -mprefergot -musermode -multcost=@var{number} -mdiv=@var{strategy} @gol |
| -mdivsi3_libfunc=@var{name} -mfixed-range=@var{register-range} @gol |
| -mindexed-addressing -mgettrcost=@var{number} -mpt-fixed @gol |
| -maccumulate-outgoing-args -minvalid-symbols -msoft-atomic -mhard-atomic @gol |
| -mbranch-cost=@var{num} -mzdcbranch -mno-zdcbranch -mcbranchdi -mcmpeqdi @gol |
| -mfused-madd -mno-fused-madd -mfsca -mno-fsca -mfsrra -mno-fsrra @gol |
| -mpretend-cmove -mtas} |
| |
| @emph{Solaris 2 Options} |
| @gccoptlist{-mimpure-text -mno-impure-text @gol |
| -pthreads -pthread} |
| |
| @emph{SPARC Options} |
| @gccoptlist{-mcpu=@var{cpu-type} @gol |
| -mtune=@var{cpu-type} @gol |
| -mcmodel=@var{code-model} @gol |
| -mmemory-model=@var{mem-model} @gol |
| -m32 -m64 -mapp-regs -mno-app-regs @gol |
| -mfaster-structs -mno-faster-structs -mflat -mno-flat @gol |
| -mfpu -mno-fpu -mhard-float -msoft-float @gol |
| -mhard-quad-float -msoft-quad-float @gol |
| -mlittle-endian @gol |
| -mstack-bias -mno-stack-bias @gol |
| -munaligned-doubles -mno-unaligned-doubles @gol |
| -mv8plus -mno-v8plus -mvis -mno-vis @gol |
| -mvis2 -mno-vis2 -mvis3 -mno-vis3 @gol |
| -mfmaf -mno-fmaf -mpopc -mno-popc @gol |
| -mfix-at697f} |
| |
| @emph{SPU Options} |
| @gccoptlist{-mwarn-reloc -merror-reloc @gol |
| -msafe-dma -munsafe-dma @gol |
| -mbranch-hints @gol |
| -msmall-mem -mlarge-mem -mstdmain @gol |
| -mfixed-range=@var{register-range} @gol |
| -mea32 -mea64 @gol |
| -maddress-space-conversion -mno-address-space-conversion @gol |
| -mcache-size=@var{cache-size} @gol |
| -matomic-updates -mno-atomic-updates} |
| |
| @emph{System V Options} |
| @gccoptlist{-Qy -Qn -YP,@var{paths} -Ym,@var{dir}} |
| |
| @emph{TILE-Gx Options} |
| @gccoptlist{-mcpu=@var{cpu} -m32 -m64 -mcmodel=@var{code-model}} |
| |
| @emph{TILEPro Options} |
| @gccoptlist{-mcpu=@var{cpu} -m32} |
| |
| @emph{V850 Options} |
| @gccoptlist{-mlong-calls -mno-long-calls -mep -mno-ep @gol |
| -mprolog-function -mno-prolog-function -mspace @gol |
| -mtda=@var{n} -msda=@var{n} -mzda=@var{n} @gol |
| -mapp-regs -mno-app-regs @gol |
| -mdisable-callt -mno-disable-callt @gol |
| -mv850e2v3 @gol |
| -mv850e2 @gol |
| -mv850e1 -mv850es @gol |
| -mv850e @gol |
| -mv850 -mbig-switch} |
| |
| @emph{VAX Options} |
| @gccoptlist{-mg -mgnu -munix} |
| |
| @emph{VMS Options} |
| @gccoptlist{-mvms-return-codes -mdebug-main=@var{prefix} -mmalloc64 @gol |
| -mpointer-size=@var{size}} |
| |
| @emph{VxWorks Options} |
| @gccoptlist{-mrtp -non-static -Bstatic -Bdynamic @gol |
| -Xbind-lazy -Xbind-now} |
| |
| @emph{x86-64 Options} |
| See i386 and x86-64 Options. |
| |
| @emph{Xstormy16 Options} |
| @gccoptlist{-msim} |
| |
| @emph{Xtensa Options} |
| @gccoptlist{-mconst16 -mno-const16 @gol |
| -mfused-madd -mno-fused-madd @gol |
| -mforce-no-pic @gol |
| -mserialize-volatile -mno-serialize-volatile @gol |
| -mtext-section-literals -mno-text-section-literals @gol |
| -mtarget-align -mno-target-align @gol |
| -mlongcalls -mno-longcalls} |
| |
| @emph{zSeries Options} |
| See S/390 and zSeries Options. |
| |
| @item Code Generation Options |
| @xref{Code Gen Options,,Options for Code Generation Conventions}. |
| @gccoptlist{-fcall-saved-@var{reg} -fcall-used-@var{reg} @gol |
| -ffixed-@var{reg} -fexceptions @gol |
| -fnon-call-exceptions -fdelete-dead-exceptions -funwind-tables @gol |
| -fasynchronous-unwind-tables @gol |
| -finhibit-size-directive -finstrument-functions @gol |
| -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} @gol |
| -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} @gol |
| -fno-common -fno-ident @gol |
| -fpcc-struct-return -fpic -fPIC -fpie -fPIE @gol |
| -fno-jump-tables @gol |
| -frecord-gcc-switches @gol |
| -freg-struct-return -fshort-enums @gol |
| -fshort-double -fshort-wchar @gol |
| -fverbose-asm -fpack-struct[=@var{n}] -fstack-check @gol |
| -fstack-limit-register=@var{reg} -fstack-limit-symbol=@var{sym} @gol |
| -fno-stack-limit -fsplit-stack @gol |
| -fleading-underscore -ftls-model=@var{model} @gol |
| -fstack-reuse=@var{reuse_level} @gol |
| -ftrapv -fwrapv -fbounds-check @gol |
| -fvisibility -fstrict-volatile-bitfields -fsync-libcalls} |
| @end table |
| |
| @menu |
| * Overall Options:: Controlling the kind of output: |
| an executable, object files, assembler files, |
| or preprocessed source. |
| * C Dialect Options:: Controlling the variant of C language compiled. |
| * C++ Dialect Options:: Variations on C++. |
| * Objective-C and Objective-C++ Dialect Options:: Variations on Objective-C |
| and Objective-C++. |
| * Language Independent Options:: Controlling how diagnostics should be |
| formatted. |
| * Warning Options:: How picky should the compiler be? |
| * Debugging Options:: Symbol tables, measurements, and debugging dumps. |
| * Optimize Options:: How much optimization? |
| * Preprocessor Options:: Controlling header files and macro definitions. |
| Also, getting dependency information for Make. |
| * Assembler Options:: Passing options to the assembler. |
| * Link Options:: Specifying libraries and so on. |
| * Directory Options:: Where to find header files and libraries. |
| Where to find the compiler executable files. |
| * Spec Files:: How to pass switches to sub-processes. |
| * Target Options:: Running a cross-compiler, or an old version of GCC. |
| @end menu |
| |
| @node Overall Options |
| @section Options Controlling the Kind of Output |
| |
| Compilation can involve up to four stages: preprocessing, compilation |
| proper, assembly and linking, always in that order. GCC is capable of |
| preprocessing and compiling several files either into several |
| assembler input files, or into one assembler input file; then each |
| assembler input file produces an object file, and linking combines all |
| the object files (those newly compiled, and those specified as input) |
| into an executable file. |
| |
| @cindex file name suffix |
| For any given input file, the file name suffix determines what kind of |
| compilation is done: |
| |
| @table @gcctabopt |
| @item @var{file}.c |
| C source code that must be preprocessed. |
| |
| @item @var{file}.i |
| C source code that should not be preprocessed. |
| |
| @item @var{file}.ii |
| C++ source code that should not be preprocessed. |
| |
| @item @var{file}.m |
| Objective-C source code. Note that you must link with the @file{libobjc} |
| library to make an Objective-C program work. |
| |
| @item @var{file}.mi |
| Objective-C source code that should not be preprocessed. |
| |
| @item @var{file}.mm |
| @itemx @var{file}.M |
| Objective-C++ source code. Note that you must link with the @file{libobjc} |
| library to make an Objective-C++ program work. Note that @samp{.M} refers |
| to a literal capital M@. |
| |
| @item @var{file}.mii |
| Objective-C++ source code that should not be preprocessed. |
| |
| @item @var{file}.h |
| C, C++, Objective-C or Objective-C++ header file to be turned into a |
| precompiled header (default), or C, C++ header file to be turned into an |
| Ada spec (via the @option{-fdump-ada-spec} switch). |
| |
| @item @var{file}.cc |
| @itemx @var{file}.cp |
| @itemx @var{file}.cxx |
| @itemx @var{file}.cpp |
| @itemx @var{file}.CPP |
| @itemx @var{file}.c++ |
| @itemx @var{file}.C |
| C++ source code that must be preprocessed. Note that in @samp{.cxx}, |
| the last two letters must both be literally @samp{x}. Likewise, |
| @samp{.C} refers to a literal capital C@. |
| |
| @item @var{file}.mm |
| @itemx @var{file}.M |
| Objective-C++ source code that must be preprocessed. |
| |
| @item @var{file}.mii |
| Objective-C++ source code that should not be preprocessed. |
| |
| @item @var{file}.hh |
| @itemx @var{file}.H |
| @itemx @var{file}.hp |
| @itemx @var{file}.hxx |
| @itemx @var{file}.hpp |
| @itemx @var{file}.HPP |
| @itemx @var{file}.h++ |
| @itemx @var{file}.tcc |
| C++ header file to be turned into a precompiled header or Ada spec. |
| |
| @item @var{file}.f |
| @itemx @var{file}.for |
| @itemx @var{file}.ftn |
| Fixed form Fortran source code that should not be preprocessed. |
| |
| @item @var{file}.F |
| @itemx @var{file}.FOR |
| @itemx @var{file}.fpp |
| @itemx @var{file}.FPP |
| @itemx @var{file}.FTN |
| Fixed form Fortran source code that must be preprocessed (with the traditional |
| preprocessor). |
| |
| @item @var{file}.f90 |
| @itemx @var{file}.f95 |
| @itemx @var{file}.f03 |
| @itemx @var{file}.f08 |
| Free form Fortran source code that should not be preprocessed. |
| |
| @item @var{file}.F90 |
| @itemx @var{file}.F95 |
| @itemx @var{file}.F03 |
| @itemx @var{file}.F08 |
| Free form Fortran source code that must be preprocessed (with the |
| traditional preprocessor). |
| |
| @item @var{file}.go |
| Go source code. |
| |
| @c FIXME: Descriptions of Java file types. |
| @c @var{file}.java |
| @c @var{file}.class |
| @c @var{file}.zip |
| @c @var{file}.jar |
| |
| @item @var{file}.ads |
| Ada source code file that contains a library unit declaration (a |
| declaration of a package, subprogram, or generic, or a generic |
| instantiation), or a library unit renaming declaration (a package, |
| generic, or subprogram renaming declaration). Such files are also |
| called @dfn{specs}. |
| |
| @item @var{file}.adb |
| Ada source code file containing a library unit body (a subprogram or |
| package body). Such files are also called @dfn{bodies}. |
| |
| @c GCC also knows about some suffixes for languages not yet included: |
| @c Pascal: |
| @c @var{file}.p |
| @c @var{file}.pas |
| @c Ratfor: |
| @c @var{file}.r |
| |
| @item @var{file}.s |
| Assembler code. |
| |
| @item @var{file}.S |
| @itemx @var{file}.sx |
| Assembler code that must be preprocessed. |
| |
| @item @var{other} |
| An object file to be fed straight into linking. |
| Any file name with no recognized suffix is treated this way. |
| @end table |
| |
| @opindex x |
| You can specify the input language explicitly with the @option{-x} option: |
| |
| @table @gcctabopt |
| @item -x @var{language} |
| Specify explicitly the @var{language} for the following input files |
| (rather than letting the compiler choose a default based on the file |
| name suffix). This option applies to all following input files until |
| the next @option{-x} option. Possible values for @var{language} are: |
| @smallexample |
| c c-header cpp-output |
| c++ c++-header c++-cpp-output |
| objective-c objective-c-header objective-c-cpp-output |
| objective-c++ objective-c++-header objective-c++-cpp-output |
| assembler assembler-with-cpp |
| ada |
| f77 f77-cpp-input f95 f95-cpp-input |
| go |
| java |
| @end smallexample |
| |
| @item -x none |
| Turn off any specification of a language, so that subsequent files are |
| handled according to their file name suffixes (as they are if @option{-x} |
| has not been used at all). |
| |
| @item -pass-exit-codes |
| @opindex pass-exit-codes |
| Normally the @command{gcc} program exits with the code of 1 if any |
| phase of the compiler returns a non-success return code. If you specify |
| @option{-pass-exit-codes}, the @command{gcc} program instead returns with |
| the numerically highest error produced by any phase returning an error |
| indication. The C, C++, and Fortran front ends return 4 if an internal |
| compiler error is encountered. |
| @end table |
| |
| If you only want some of the stages of compilation, you can use |
| @option{-x} (or filename suffixes) to tell @command{gcc} where to start, and |
| one of the options @option{-c}, @option{-S}, or @option{-E} to say where |
| @command{gcc} is to stop. Note that some combinations (for example, |
| @samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all. |
| |
| @table @gcctabopt |
| @item -c |
| @opindex c |
| Compile or assemble the source files, but do not link. The linking |
| stage simply is not done. The ultimate output is in the form of an |
| object file for each source file. |
| |
| By default, the object file name for a source file is made by replacing |
| the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}. |
| |
| Unrecognized input files, not requiring compilation or assembly, are |
| ignored. |
| |
| @item -S |
| @opindex S |
| Stop after the stage of compilation proper; do not assemble. The output |
| is in the form of an assembler code file for each non-assembler input |
| file specified. |
| |
| By default, the assembler file name for a source file is made by |
| replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}. |
| |
| Input files that don't require compilation are ignored. |
| |
| @item -E |
| @opindex E |
| Stop after the preprocessing stage; do not run the compiler proper. The |
| output is in the form of preprocessed source code, which is sent to the |
| standard output. |
| |
| Input files that don't require preprocessing are ignored. |
| |
| @cindex output file option |
| @item -o @var{file} |
| @opindex o |
| Place output in file @var{file}. This applies to whatever |
| sort of output is being produced, whether it be an executable file, |
| an object file, an assembler file or preprocessed C code. |
| |
| If @option{-o} is not specified, the default is to put an executable |
| file in @file{a.out}, the object file for |
| @file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its |
| assembler file in @file{@var{source}.s}, a precompiled header file in |
| @file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on |
| standard output. |
| |
| @item -v |
| @opindex v |
| Print (on standard error output) the commands executed to run the stages |
| of compilation. Also print the version number of the compiler driver |
| program and of the preprocessor and the compiler proper. |
| |
| @item -### |
| @opindex ### |
| Like @option{-v} except the commands are not executed and arguments |
| are quoted unless they contain only alphanumeric characters or @code{./-_}. |
| This is useful for shell scripts to capture the driver-generated command lines. |
| |
| @item -pipe |
| @opindex pipe |
| Use pipes rather than temporary files for communication between the |
| various stages of compilation. This fails to work on some systems where |
| the assembler is unable to read from a pipe; but the GNU assembler has |
| no trouble. |
| |
| @item --help |
| @opindex help |
| Print (on the standard output) a description of the command-line options |
| understood by @command{gcc}. If the @option{-v} option is also specified |
| then @option{--help} is also passed on to the various processes |
| invoked by @command{gcc}, so that they can display the command-line options |
| they accept. If the @option{-Wextra} option has also been specified |
| (prior to the @option{--help} option), then command-line options that |
| have no documentation associated with them are also displayed. |
| |
| @item --target-help |
| @opindex target-help |
| Print (on the standard output) a description of target-specific command-line |
| options for each tool. For some targets extra target-specific |
| information may also be printed. |
| |
| @item --help=@{@var{class}@r{|[}^@r{]}@var{qualifier}@}@r{[},@dots{}@r{]} |
| Print (on the standard output) a description of the command-line |
| options understood by the compiler that fit into all specified classes |
| and qualifiers. These are the supported classes: |
| |
| @table @asis |
| @item @samp{optimizers} |
| Display all of the optimization options supported by the |
| compiler. |
| |
| @item @samp{warnings} |
| Display all of the options controlling warning messages |
| produced by the compiler. |
| |
| @item @samp{target} |
| Display target-specific options. Unlike the |
| @option{--target-help} option however, target-specific options of the |
| linker and assembler are not displayed. This is because those |
| tools do not currently support the extended @option{--help=} syntax. |
| |
| @item @samp{params} |
| Display the values recognized by the @option{--param} |
| option. |
| |
| @item @var{language} |
| Display the options supported for @var{language}, where |
| @var{language} is the name of one of the languages supported in this |
| version of GCC@. |
| |
| @item @samp{common} |
| Display the options that are common to all languages. |
| @end table |
| |
| These are the supported qualifiers: |
| |
| @table @asis |
| @item @samp{undocumented} |
| Display only those options that are undocumented. |
| |
| @item @samp{joined} |
| Display options taking an argument that appears after an equal |
| sign in the same continuous piece of text, such as: |
| @samp{--help=target}. |
| |
| @item @samp{separate} |
| Display options taking an argument that appears as a separate word |
| following the original option, such as: @samp{-o output-file}. |
| @end table |
| |
| Thus for example to display all the undocumented target-specific |
| switches supported by the compiler, use: |
| |
| @smallexample |
| --help=target,undocumented |
| @end smallexample |
| |
| The sense of a qualifier can be inverted by prefixing it with the |
| @samp{^} character, so for example to display all binary warning |
| options (i.e., ones that are either on or off and that do not take an |
| argument) that have a description, use: |
| |
| @smallexample |
| --help=warnings,^joined,^undocumented |
| @end smallexample |
| |
| The argument to @option{--help=} should not consist solely of inverted |
| qualifiers. |
| |
| Combining several classes is possible, although this usually |
| restricts the output so much that there is nothing to display. One |
| case where it does work, however, is when one of the classes is |
| @var{target}. For example, to display all the target-specific |
| optimization options, use: |
| |
| @smallexample |
| --help=target,optimizers |
| @end smallexample |
| |
| The @option{--help=} option can be repeated on the command line. Each |
| successive use displays its requested class of options, skipping |
| those that have already been displayed. |
| |
| If the @option{-Q} option appears on the command line before the |
| @option{--help=} option, then the descriptive text displayed by |
| @option{--help=} is changed. Instead of describing the displayed |
| options, an indication is given as to whether the option is enabled, |
| disabled or set to a specific value (assuming that the compiler |
| knows this at the point where the @option{--help=} option is used). |
| |
| Here is a truncated example from the ARM port of @command{gcc}: |
| |
| @smallexample |
| % gcc -Q -mabi=2 --help=target -c |
| The following options are target specific: |
| -mabi= 2 |
| -mabort-on-noreturn [disabled] |
| -mapcs [disabled] |
| @end smallexample |
| |
| The output is sensitive to the effects of previous command-line |
| options, so for example it is possible to find out which optimizations |
| are enabled at @option{-O2} by using: |
| |
| @smallexample |
| -Q -O2 --help=optimizers |
| @end smallexample |
| |
| Alternatively you can discover which binary optimizations are enabled |
| by @option{-O3} by using: |
| |
| @smallexample |
| gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts |
| gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts |
| diff /tmp/O2-opts /tmp/O3-opts | grep enabled |
| @end smallexample |
| |
| @item -no-canonical-prefixes |
| @opindex no-canonical-prefixes |
| Do not expand any symbolic links, resolve references to @samp{/../} |
| or @samp{/./}, or make the path absolute when generating a relative |
| prefix. |
| |
| @item --version |
| @opindex version |
| Display the version number and copyrights of the invoked GCC@. |
| |
| @item -wrapper |
| @opindex wrapper |
| Invoke all subcommands under a wrapper program. The name of the |
| wrapper program and its parameters are passed as a comma separated |
| list. |
| |
| @smallexample |
| gcc -c t.c -wrapper gdb,--args |
| @end smallexample |
| |
| @noindent |
| This invokes all subprograms of @command{gcc} under |
| @samp{gdb --args}, thus the invocation of @command{cc1} is |
| @samp{gdb --args cc1 @dots{}}. |
| |
| @item -fplugin=@var{name}.so |
| Load the plugin code in file @var{name}.so, assumed to be a |
| shared object to be dlopen'd by the compiler. The base name of |
| the shared object file is used to identify the plugin for the |
| purposes of argument parsing (See |
| @option{-fplugin-arg-@var{name}-@var{key}=@var{value}} below). |
| Each plugin should define the callback functions specified in the |
| Plugins API. |
| |
| @item -fplugin-arg-@var{name}-@var{key}=@var{value} |
| Define an argument called @var{key} with a value of @var{value} |
| for the plugin called @var{name}. |
| |
| @item -fdump-ada-spec@r{[}-slim@r{]} |
| For C and C++ source and include files, generate corresponding Ada |
| specs. @xref{Generating Ada Bindings for C and C++ headers,,, gnat_ugn, |
| GNAT User's Guide}, which provides detailed documentation on this feature. |
| |
| @item -fdump-go-spec=@var{file} |
| For input files in any language, generate corresponding Go |
| declarations in @var{file}. This generates Go @code{const}, |
| @code{type}, @code{var}, and @code{func} declarations which may be a |
| useful way to start writing a Go interface to code written in some |
| other language. |
| |
| @include @value{srcdir}/../libiberty/at-file.texi |
| @end table |
| |
| @node Invoking G++ |
| @section Compiling C++ Programs |
| |
| @cindex suffixes for C++ source |
| @cindex C++ source file suffixes |
| C++ source files conventionally use one of the suffixes @samp{.C}, |
| @samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or |
| @samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp}, |
| @samp{.H}, or (for shared template code) @samp{.tcc}; and |
| preprocessed C++ files use the suffix @samp{.ii}. GCC recognizes |
| files with these names and compiles them as C++ programs even if you |
| call the compiler the same way as for compiling C programs (usually |
| with the name @command{gcc}). |
| |
| @findex g++ |
| @findex c++ |
| However, the use of @command{gcc} does not add the C++ library. |
| @command{g++} is a program that calls GCC and automatically specifies linking |
| against the C++ library. It treats @samp{.c}, |
| @samp{.h} and @samp{.i} files as C++ source files instead of C source |
| files unless @option{-x} is used. This program is also useful when |
| precompiling a C header file with a @samp{.h} extension for use in C++ |
| compilations. On many systems, @command{g++} is also installed with |
| the name @command{c++}. |
| |
| @cindex invoking @command{g++} |
| When you compile C++ programs, you may specify many of the same |
| command-line options that you use for compiling programs in any |
| language; or command-line options meaningful for C and related |
| languages; or options that are meaningful only for C++ programs. |
| @xref{C Dialect Options,,Options Controlling C Dialect}, for |
| explanations of options for languages related to C@. |
| @xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for |
| explanations of options that are meaningful only for C++ programs. |
| |
| @node C Dialect Options |
| @section Options Controlling C Dialect |
| @cindex dialect options |
| @cindex language dialect options |
| @cindex options, dialect |
| |
| The following options control the dialect of C (or languages derived |
| from C, such as C++, Objective-C and Objective-C++) that the compiler |
| accepts: |
| |
| @table @gcctabopt |
| @cindex ANSI support |
| @cindex ISO support |
| @item -ansi |
| @opindex ansi |
| In C mode, this is equivalent to @option{-std=c90}. In C++ mode, it is |
| equivalent to @option{-std=c++98}. |
| |
| This turns off certain features of GCC that are incompatible with ISO |
| C90 (when compiling C code), or of standard C++ (when compiling C++ code), |
| such as the @code{asm} and @code{typeof} keywords, and |
| predefined macros such as @code{unix} and @code{vax} that identify the |
| type of system you are using. It also enables the undesirable and |
| rarely used ISO trigraph feature. For the C compiler, |
| it disables recognition of C++ style @samp{//} comments as well as |
| the @code{inline} keyword. |
| |
| The alternate keywords @code{__asm__}, @code{__extension__}, |
| @code{__inline__} and @code{__typeof__} continue to work despite |
| @option{-ansi}. You would not want to use them in an ISO C program, of |
| course, but it is useful to put them in header files that might be included |
| in compilations done with @option{-ansi}. Alternate predefined macros |
| such as @code{__unix__} and @code{__vax__} are also available, with or |
| without @option{-ansi}. |
| |
| The @option{-ansi} option does not cause non-ISO programs to be |
| rejected gratuitously. For that, @option{-Wpedantic} is required in |
| addition to @option{-ansi}. @xref{Warning Options}. |
| |
| The macro @code{__STRICT_ANSI__} is predefined when the @option{-ansi} |
| option is used. Some header files may notice this macro and refrain |
| from declaring certain functions or defining certain macros that the |
| ISO standard doesn't call for; this is to avoid interfering with any |
| programs that might use these names for other things. |
| |
| Functions that are normally built in but do not have semantics |
| defined by ISO C (such as @code{alloca} and @code{ffs}) are not built-in |
| functions when @option{-ansi} is used. @xref{Other Builtins,,Other |
| built-in functions provided by GCC}, for details of the functions |
| affected. |
| |
| @item -std= |
| @opindex std |
| Determine the language standard. @xref{Standards,,Language Standards |
| Supported by GCC}, for details of these standard versions. This option |
| is currently only supported when compiling C or C++. |
| |
| The compiler can accept several base standards, such as @samp{c90} or |
| @samp{c++98}, and GNU dialects of those standards, such as |
| @samp{gnu90} or @samp{gnu++98}. When a base standard is specified, the |
| compiler accepts all programs following that standard plus those |
| using GNU extensions that do not contradict it. For example, |
| @option{-std=c90} turns off certain features of GCC that are |
| incompatible with ISO C90, such as the @code{asm} and @code{typeof} |
| keywords, but not other GNU extensions that do not have a meaning in |
| ISO C90, such as omitting the middle term of a @code{?:} |
| expression. On the other hand, when a GNU dialect of a standard is |
| specified, all features supported by the compiler are enabled, even when |
| those features change the meaning of the base standard. As a result, some |
| strict-conforming programs may be rejected. The particular standard |
| is used by @option{-Wpedantic} to identify which features are GNU |
| extensions given that version of the standard. For example |
| @option{-std=gnu90 -Wpedantic} warns about C++ style @samp{//} |
| comments, while @option{-std=gnu99 -Wpedantic} does not. |
| |
| A value for this option must be provided; possible values are |
| |
| @table @samp |
| @item c90 |
| @itemx c89 |
| @itemx iso9899:1990 |
| Support all ISO C90 programs (certain GNU extensions that conflict |
| with ISO C90 are disabled). Same as @option{-ansi} for C code. |
| |
| @item iso9899:199409 |
| ISO C90 as modified in amendment 1. |
| |
| @item c99 |
| @itemx c9x |
| @itemx iso9899:1999 |
| @itemx iso9899:199x |
| ISO C99. Note that this standard is not yet fully supported; see |
| @w{@uref{http://gcc.gnu.org/c99status.html}} for more information. The |
| names @samp{c9x} and @samp{iso9899:199x} are deprecated. |
| |
| @item c11 |
| @itemx c1x |
| @itemx iso9899:2011 |
| ISO C11, the 2011 revision of the ISO C standard. |
| Support is incomplete and experimental. The name @samp{c1x} is |
| deprecated. |
| |
| @item gnu90 |
| @itemx gnu89 |
| GNU dialect of ISO C90 (including some C99 features). This |
| is the default for C code. |
| |
| @item gnu99 |
| @itemx gnu9x |
| GNU dialect of ISO C99. When ISO C99 is fully implemented in GCC, |
| this will become the default. The name @samp{gnu9x} is deprecated. |
| |
| @item gnu11 |
| @item gnu1x |
| GNU dialect of ISO C11. Support is incomplete and experimental. The |
| name @samp{gnu1x} is deprecated. |
| |
| @item c++98 |
| @itemx c++03 |
| The 1998 ISO C++ standard plus the 2003 technical corrigendum and some |
| additional defect reports. Same as @option{-ansi} for C++ code. |
| |
| @item gnu++98 |
| @itemx gnu++03 |
| GNU dialect of @option{-std=c++98}. This is the default for |
| C++ code. |
| |
| @item c++11 |
| @itemx c++0x |
| The 2011 ISO C++ standard plus amendments. Support for C++11 is still |
| experimental, and may change in incompatible ways in future releases. |
| The name @samp{c++0x} is deprecated. |
| |
| @item gnu++11 |
| @itemx gnu++0x |
| GNU dialect of @option{-std=c++11}. Support for C++11 is still |
| experimental, and may change in incompatible ways in future releases. |
| The name @samp{gnu++0x} is deprecated. |
| |
| @item c++1y |
| The next revision of the ISO C++ standard, tentatively planned for |
| 2017. Support is highly experimental, and will almost certainly |
| change in incompatible ways in future releases. |
| |
| @item gnu++1y |
| GNU dialect of @option{-std=c++1y}. Support is highly experimental, |
| and will almost certainly change in incompatible ways in future |
| releases. |
| @end table |
| |
| @item -fgnu89-inline |
| @opindex fgnu89-inline |
| The option @option{-fgnu89-inline} tells GCC to use the traditional |
| GNU semantics for @code{inline} functions when in C99 mode. |
| @xref{Inline,,An Inline Function is As Fast As a Macro}. This option |
| is accepted and ignored by GCC versions 4.1.3 up to but not including |
| 4.3. In GCC versions 4.3 and later it changes the behavior of GCC in |
| C99 mode. Using this option is roughly equivalent to adding the |
| @code{gnu_inline} function attribute to all inline functions |
| (@pxref{Function Attributes}). |
| |
| The option @option{-fno-gnu89-inline} explicitly tells GCC to use the |
| C99 semantics for @code{inline} when in C99 or gnu99 mode (i.e., it |
| specifies the default behavior). This option was first supported in |
| GCC 4.3. This option is not supported in @option{-std=c90} or |
| @option{-std=gnu90} mode. |
| |
| The preprocessor macros @code{__GNUC_GNU_INLINE__} and |
| @code{__GNUC_STDC_INLINE__} may be used to check which semantics are |
| in effect for @code{inline} functions. @xref{Common Predefined |
| Macros,,,cpp,The C Preprocessor}. |
| |
| @item -aux-info @var{filename} |
| @opindex aux-info |
| Output to the given filename prototyped declarations for all functions |
| declared and/or defined in a translation unit, including those in header |
| files. This option is silently ignored in any language other than C@. |
| |
| Besides declarations, the file indicates, in comments, the origin of |
| each declaration (source file and line), whether the declaration was |
| implicit, prototyped or unprototyped (@samp{I}, @samp{N} for new or |
| @samp{O} for old, respectively, in the first character after the line |
| number and the colon), and whether it came from a declaration or a |
| definition (@samp{C} or @samp{F}, respectively, in the following |
| character). In the case of function definitions, a K&R-style list of |
| arguments followed by their declarations is also provided, inside |
| comments, after the declaration. |
| |
| @item -fallow-parameterless-variadic-functions |
| Accept variadic functions without named parameters. |
| |
| Although it is possible to define such a function, this is not very |
| useful as it is not possible to read the arguments. This is only |
| supported for C as this construct is allowed by C++. |
| |
| @item -fno-asm |
| @opindex fno-asm |
| Do not recognize @code{asm}, @code{inline} or @code{typeof} as a |
| keyword, so that code can use these words as identifiers. You can use |
| the keywords @code{__asm__}, @code{__inline__} and @code{__typeof__} |
| instead. @option{-ansi} implies @option{-fno-asm}. |
| |
| In C++, this switch only affects the @code{typeof} keyword, since |
| @code{asm} and @code{inline} are standard keywords. You may want to |
| use the @option{-fno-gnu-keywords} flag instead, which has the same |
| effect. In C99 mode (@option{-std=c99} or @option{-std=gnu99}), this |
| switch only affects the @code{asm} and @code{typeof} keywords, since |
| @code{inline} is a standard keyword in ISO C99. |
| |
| @item -fno-builtin |
| @itemx -fno-builtin-@var{function} |
| @opindex fno-builtin |
| @cindex built-in functions |
| Don't recognize built-in functions that do not begin with |
| @samp{__builtin_} as prefix. @xref{Other Builtins,,Other built-in |
| functions provided by GCC}, for details of the functions affected, |
| including those which are not built-in functions when @option{-ansi} or |
| @option{-std} options for strict ISO C conformance are used because they |
| do not have an ISO standard meaning. |
| |
| GCC normally generates special code to handle certain built-in functions |
| more efficiently; for instance, calls to @code{alloca} may become single |
| instructions which adjust the stack directly, and calls to @code{memcpy} |
| may become inline copy loops. The resulting code is often both smaller |
| and faster, but since the function calls no longer appear as such, you |
| cannot set a breakpoint on those calls, nor can you change the behavior |
| of the functions by linking with a different library. In addition, |
| when a function is recognized as a built-in function, GCC may use |
| information about that function to warn about problems with calls to |
| that function, or to generate more efficient code, even if the |
| resulting code still contains calls to that function. For example, |
| warnings are given with @option{-Wformat} for bad calls to |
| @code{printf} when @code{printf} is built in and @code{strlen} is |
| known not to modify global memory. |
| |
| With the @option{-fno-builtin-@var{function}} option |
| only the built-in function @var{function} is |
| disabled. @var{function} must not begin with @samp{__builtin_}. If a |
| function is named that is not built-in in this version of GCC, this |
| option is ignored. There is no corresponding |
| @option{-fbuiltin-@var{function}} option; if you wish to enable |
| built-in functions selectively when using @option{-fno-builtin} or |
| @option{-ffreestanding}, you may define macros such as: |
| |
| @smallexample |
| #define abs(n) __builtin_abs ((n)) |
| #define strcpy(d, s) __builtin_strcpy ((d), (s)) |
| @end smallexample |
| |
| @item -fhosted |
| @opindex fhosted |
| @cindex hosted environment |
| |
| Assert that compilation targets a hosted environment. This implies |
| @option{-fbuiltin}. A hosted environment is one in which the |
| entire standard library is available, and in which @code{main} has a return |
| type of @code{int}. Examples are nearly everything except a kernel. |
| This is equivalent to @option{-fno-freestanding}. |
| |
| @item -ffreestanding |
| @opindex ffreestanding |
| @cindex hosted environment |
| |
| Assert that compilation targets a freestanding environment. This |
| implies @option{-fno-builtin}. A freestanding environment |
| is one in which the standard library may not exist, and program startup may |
| not necessarily be at @code{main}. The most obvious example is an OS kernel. |
| This is equivalent to @option{-fno-hosted}. |
| |
| @xref{Standards,,Language Standards Supported by GCC}, for details of |
| freestanding and hosted environments. |
| |
| @item -fopenmp |
| @opindex fopenmp |
| @cindex OpenMP parallel |
| Enable handling of OpenMP directives @code{#pragma omp} in C/C++ and |
| @code{!$omp} in Fortran. When @option{-fopenmp} is specified, the |
| compiler generates parallel code according to the OpenMP Application |
| Program Interface v3.0 @w{@uref{http://www.openmp.org/}}. This option |
| implies @option{-pthread}, and thus is only supported on targets that |
| have support for @option{-pthread}. |
| |
| @item -fgnu-tm |
| @opindex fgnu-tm |
| When the option @option{-fgnu-tm} is specified, the compiler |
| generates code for the Linux variant of Intel's current Transactional |
| Memory ABI specification document (Revision 1.1, May 6 2009). This is |
| an experimental feature whose interface may change in future versions |
| of GCC, as the official specification changes. Please note that not |
| all architectures are supported for this feature. |
| |
| For more information on GCC's support for transactional memory, |
| @xref{Enabling libitm,,The GNU Transactional Memory Library,libitm,GNU |
| Transactional Memory Library}. |
| |
| Note that the transactional memory feature is not supported with |
| non-call exceptions (@option{-fnon-call-exceptions}). |
| |
| @item -fms-extensions |
| @opindex fms-extensions |
| Accept some non-standard constructs used in Microsoft header files. |
| |
| In C++ code, this allows member names in structures to be similar |
| to previous types declarations. |
| |
| @smallexample |
| typedef int UOW; |
| struct ABC @{ |
| UOW UOW; |
| @}; |
| @end smallexample |
| |
| Some cases of unnamed fields in structures and unions are only |
| accepted with this option. @xref{Unnamed Fields,,Unnamed struct/union |
| fields within structs/unions}, for details. |
| |
| @item -fplan9-extensions |
| Accept some non-standard constructs used in Plan 9 code. |
| |
| This enables @option{-fms-extensions}, permits passing pointers to |
| structures with anonymous fields to functions that expect pointers to |
| elements of the type of the field, and permits referring to anonymous |
| fields declared using a typedef. @xref{Unnamed Fields,,Unnamed |
| struct/union fields within structs/unions}, for details. This is only |
| supported for C, not C++. |
| |
| @item -trigraphs |
| @opindex trigraphs |
| Support ISO C trigraphs. The @option{-ansi} option (and @option{-std} |
| options for strict ISO C conformance) implies @option{-trigraphs}. |
| |
| @cindex traditional C language |
| @cindex C language, traditional |
| @item -traditional |
| @itemx -traditional-cpp |
| @opindex traditional-cpp |
| @opindex traditional |
| Formerly, these options caused GCC to attempt to emulate a pre-standard |
| C compiler. They are now only supported with the @option{-E} switch. |
| The preprocessor continues to support a pre-standard mode. See the GNU |
| CPP manual for details. |
| |
| @item -fcond-mismatch |
| @opindex fcond-mismatch |
| Allow conditional expressions with mismatched types in the second and |
| third arguments. The value of such an expression is void. This option |
| is not supported for C++. |
| |
| @item -flax-vector-conversions |
| @opindex flax-vector-conversions |
| Allow implicit conversions between vectors with differing numbers of |
| elements and/or incompatible element types. This option should not be |
| used for new code. |
| |
| @item -funsigned-char |
| @opindex funsigned-char |
| Let the type @code{char} be unsigned, like @code{unsigned char}. |
| |
| Each kind of machine has a default for what @code{char} should |
| be. It is either like @code{unsigned char} by default or like |
| @code{signed char} by default. |
| |
| Ideally, a portable program should always use @code{signed char} or |
| @code{unsigned char} when it depends on the signedness of an object. |
| But many programs have been written to use plain @code{char} and |
| expect it to be signed, or expect it to be unsigned, depending on the |
| machines they were written for. This option, and its inverse, let you |
| make such a program work with the opposite default. |
| |
| The type @code{char} is always a distinct type from each of |
| @code{signed char} or @code{unsigned char}, even though its behavior |
| is always just like one of those two. |
| |
| @item -fsigned-char |
| @opindex fsigned-char |
| Let the type @code{char} be signed, like @code{signed char}. |
| |
| Note that this is equivalent to @option{-fno-unsigned-char}, which is |
| the negative form of @option{-funsigned-char}. Likewise, the option |
| @option{-fno-signed-char} is equivalent to @option{-funsigned-char}. |
| |
| @item -fsigned-bitfields |
| @itemx -funsigned-bitfields |
| @itemx -fno-signed-bitfields |
| @itemx -fno-unsigned-bitfields |
| @opindex fsigned-bitfields |
| @opindex funsigned-bitfields |
| @opindex fno-signed-bitfields |
| @opindex fno-unsigned-bitfields |
| These options control whether a bit-field is signed or unsigned, when the |
| declaration does not use either @code{signed} or @code{unsigned}. By |
| default, such a bit-field is signed, because this is consistent: the |
| basic integer types such as @code{int} are signed types. |
| @end table |
| |
| @node C++ Dialect Options |
| @section Options Controlling C++ Dialect |
| |
| @cindex compiler options, C++ |
| @cindex C++ options, command-line |
| @cindex options, C++ |
| This section describes the command-line options that are only meaningful |
| for C++ programs. You can also use most of the GNU compiler options |
| regardless of what language your program is in. For example, you |
| might compile a file @code{firstClass.C} like this: |
| |
| @smallexample |
| g++ -g -frepo -O -c firstClass.C |
| @end smallexample |
| |
| @noindent |
| In this example, only @option{-frepo} is an option meant |
| only for C++ programs; you can use the other options with any |
| language supported by GCC@. |
| |
| Here is a list of options that are @emph{only} for compiling C++ programs: |
| |
| @table @gcctabopt |
| |
| @item -fabi-version=@var{n} |
| @opindex fabi-version |
| Use version @var{n} of the C++ ABI@. The default is version 2. |
| |
| Version 0 refers to the version conforming most closely to |
| the C++ ABI specification. Therefore, the ABI obtained using version 0 |
| will change in different versions of G++ as ABI bugs are fixed. |
| |
| Version 1 is the version of the C++ ABI that first appeared in G++ 3.2. |
| |
| Version 2 is the version of the C++ ABI that first appeared in G++ 3.4. |
| |
| Version 3 corrects an error in mangling a constant address as a |
| template argument. |
| |
| Version 4, which first appeared in G++ 4.5, implements a standard |
| mangling for vector types. |
| |
| Version 5, which first appeared in G++ 4.6, corrects the mangling of |
| attribute const/volatile on function pointer types, decltype of a |
| plain decl, and use of a function parameter in the declaration of |
| another parameter. |
| |
| Version 6, which first appeared in G++ 4.7, corrects the promotion |
| behavior of C++11 scoped enums and the mangling of template argument |
| packs, const/static_cast, prefix ++ and --, and a class scope function |
| used as a template argument. |
| |
| See also @option{-Wabi}. |
| |
| @item -fno-access-control |
| @opindex fno-access-control |
| Turn off all access checking. This switch is mainly useful for working |
| around bugs in the access control code. |
| |
| @item -fcheck-new |
| @opindex fcheck-new |
| Check that the pointer returned by @code{operator new} is non-null |
| before attempting to modify the storage allocated. This check is |
| normally unnecessary because the C++ standard specifies that |
| @code{operator new} only returns @code{0} if it is declared |
| @samp{throw()}, in which case the compiler always checks the |
| return value even without this option. In all other cases, when |
| @code{operator new} has a non-empty exception specification, memory |
| exhaustion is signalled by throwing @code{std::bad_alloc}. See also |
| @samp{new (nothrow)}. |
| |
| @item -fconstexpr-depth=@var{n} |
| @opindex fconstexpr-depth |
| Set the maximum nested evaluation depth for C++11 constexpr functions |
| to @var{n}. A limit is needed to detect endless recursion during |
| constant expression evaluation. The minimum specified by the standard |
| is 512. |
| |
| @item -fdeduce-init-list |
| @opindex fdeduce-init-list |
| Enable deduction of a template type parameter as |
| @code{std::initializer_list} from a brace-enclosed initializer list, i.e.@: |
| |
| @smallexample |
| template <class T> auto forward(T t) -> decltype (realfn (t)) |
| @{ |
| return realfn (t); |
| @} |
| |
| void f() |
| @{ |
| forward(@{1,2@}); // call forward<std::initializer_list<int>> |
| @} |
| @end smallexample |
| |
| This deduction was implemented as a possible extension to the |
| originally proposed semantics for the C++11 standard, but was not part |
| of the final standard, so it is disabled by default. This option is |
| deprecated, and may be removed in a future version of G++. |
| |
| @item -ffriend-injection |
| @opindex ffriend-injection |
| Inject friend functions into the enclosing namespace, so that they are |
| visible outside the scope of the class in which they are declared. |
| Friend functions were documented to work this way in the old Annotated |
| C++ Reference Manual, and versions of G++ before 4.1 always worked |
| that way. However, in ISO C++ a friend function that is not declared |
| in an enclosing scope can only be found using argument dependent |
| lookup. This option causes friends to be injected as they were in |
| earlier releases. |
| |
| This option is for compatibility, and may be removed in a future |
| release of G++. |
| |
| @item -fno-elide-constructors |
| @opindex fno-elide-constructors |
| The C++ standard allows an implementation to omit creating a temporary |
| that is only used to initialize another object of the same type. |
| Specifying this option disables that optimization, and forces G++ to |
| call the copy constructor in all cases. |
| |
| @item -fno-enforce-eh-specs |
| @opindex fno-enforce-eh-specs |
| Don't generate code to check for violation of exception specifications |
| at run time. This option violates the C++ standard, but may be useful |
| for reducing code size in production builds, much like defining |
| @samp{NDEBUG}. This does not give user code permission to throw |
| exceptions in violation of the exception specifications; the compiler |
| still optimizes based on the specifications, so throwing an |
| unexpected exception results in undefined behavior at run time. |
| |
| @item -ffor-scope |
| @itemx -fno-for-scope |
| @opindex ffor-scope |
| @opindex fno-for-scope |
| If @option{-ffor-scope} is specified, the scope of variables declared in |
| a @i{for-init-statement} is limited to the @samp{for} loop itself, |
| as specified by the C++ standard. |
| If @option{-fno-for-scope} is specified, the scope of variables declared in |
| a @i{for-init-statement} extends to the end of the enclosing scope, |
| as was the case in old versions of G++, and other (traditional) |
| implementations of C++. |
| |
| If neither flag is given, the default is to follow the standard, |
| but to allow and give a warning for old-style code that would |
| otherwise be invalid, or have different behavior. |
| |
| @item -fno-gnu-keywords |
| @opindex fno-gnu-keywords |
| Do not recognize @code{typeof} as a keyword, so that code can use this |
| word as an identifier. You can use the keyword @code{__typeof__} instead. |
| @option{-ansi} implies @option{-fno-gnu-keywords}. |
| |
| @item -fno-implicit-templates |
| @opindex fno-implicit-templates |
| Never emit code for non-inline templates that are instantiated |
| implicitly (i.e.@: by use); only emit code for explicit instantiations. |
| @xref{Template Instantiation}, for more information. |
| |
| @item -fno-implicit-inline-templates |
| @opindex fno-implicit-inline-templates |
| Don't emit code for implicit instantiations of inline templates, either. |
| The default is to handle inlines differently so that compiles with and |
| without optimization need the same set of explicit instantiations. |
| |
| @item -fno-implement-inlines |
| @opindex fno-implement-inlines |
| To save space, do not emit out-of-line copies of inline functions |
| controlled by @samp{#pragma implementation}. This causes linker |
| errors if these functions are not inlined everywhere they are called. |
| |
| @item -fms-extensions |
| @opindex fms-extensions |
| Disable Wpedantic warnings about constructs used in MFC, such as implicit |
| int and getting a pointer to member function via non-standard syntax. |
| |
| @item -fno-nonansi-builtins |
| @opindex fno-nonansi-builtins |
| Disable built-in declarations of functions that are not mandated by |
| ANSI/ISO C@. These include @code{ffs}, @code{alloca}, @code{_exit}, |
| @code{index}, @code{bzero}, @code{conjf}, and other related functions. |
| |
| @item -fnothrow-opt |
| @opindex fnothrow-opt |
| Treat a @code{throw()} exception specification as if it were a |
| @code{noexcept} specification to reduce or eliminate the text size |
| overhead relative to a function with no exception specification. If |
| the function has local variables of types with non-trivial |
| destructors, the exception specification actually makes the |
| function smaller because the EH cleanups for those variables can be |
| optimized away. The semantic effect is that an exception thrown out of |
| a function with such an exception specification results in a call |
| to @code{terminate} rather than @code{unexpected}. |
| |
| @item -fno-operator-names |
| @opindex fno-operator-names |
| Do not treat the operator name keywords @code{and}, @code{bitand}, |
| @code{bitor}, @code{compl}, @code{not}, @code{or} and @code{xor} as |
| synonyms as keywords. |
| |
| @item -fno-optional-diags |
| @opindex fno-optional-diags |
| Disable diagnostics that the standard says a compiler does not need to |
| issue. Currently, the only such diagnostic issued by G++ is the one for |
| a name having multiple meanings within a class. |
| |
| @item -fpermissive |
| @opindex fpermissive |
| Downgrade some diagnostics about nonconformant code from errors to |
| warnings. Thus, using @option{-fpermissive} allows some |
| nonconforming code to compile. |
| |
| @item -fno-pretty-templates |
| @opindex fno-pretty-templates |
| When an error message refers to a specialization of a function |
| template, the compiler normally prints the signature of the |
| template followed by the template arguments and any typedefs or |
| typenames in the signature (e.g. @code{void f(T) [with T = int]} |
| rather than @code{void f(int)}) so that it's clear which template is |
| involved. When an error message refers to a specialization of a class |
| template, the compiler omits any template arguments that match |
| the default template arguments for that template. If either of these |
| behaviors make it harder to understand the error message rather than |
| easier, you can use @option{-fno-pretty-templates} to disable them. |
| |
| @item -frepo |
| @opindex frepo |
| Enable automatic template instantiation at link time. This option also |
| implies @option{-fno-implicit-templates}. @xref{Template |
| Instantiation}, for more information. |
| |
| @item -fno-rtti |
| @opindex fno-rtti |
| Disable generation of information about every class with virtual |
| functions for use by the C++ run-time type identification features |
| (@samp{dynamic_cast} and @samp{typeid}). If you don't use those parts |
| of the language, you can save some space by using this flag. Note that |
| exception handling uses the same information, but G++ generates it as |
| needed. The @samp{dynamic_cast} operator can still be used for casts that |
| do not require run-time type information, i.e.@: casts to @code{void *} or to |
| unambiguous base classes. |
| |
| @item -fstats |
| @opindex fstats |
| Emit statistics about front-end processing at the end of the compilation. |
| This information is generally only useful to the G++ development team. |
| |
| @item -fstrict-enums |
| @opindex fstrict-enums |
| Allow the compiler to optimize using the assumption that a value of |
| enumerated type can only be one of the values of the enumeration (as |
| defined in the C++ standard; basically, a value that can be |
| represented in the minimum number of bits needed to represent all the |
| enumerators). This assumption may not be valid if the program uses a |
| cast to convert an arbitrary integer value to the enumerated type. |
| |
| @item -ftemplate-backtrace-limit=@var{n} |
| @opindex ftemplate-backtrace-limit |
| Set the maximum number of template instantiation notes for a single |
| warning or error to @var{n}. The default value is 10. |
| |
| @item -ftemplate-depth=@var{n} |
| @opindex ftemplate-depth |
| Set the maximum instantiation depth for template classes to @var{n}. |
| A limit on the template instantiation depth is needed to detect |
| endless recursions during template class instantiation. ANSI/ISO C++ |
| conforming programs must not rely on a maximum depth greater than 17 |
| (changed to 1024 in C++11). The default value is 900, as the compiler |
| can run out of stack space before hitting 1024 in some situations. |
| |
| @item -fno-threadsafe-statics |
| @opindex fno-threadsafe-statics |
| Do not emit the extra code to use the routines specified in the C++ |
| ABI for thread-safe initialization of local statics. You can use this |
| option to reduce code size slightly in code that doesn't need to be |
| thread-safe. |
| |
| @item -fuse-cxa-atexit |
| @opindex fuse-cxa-atexit |
| Register destructors for objects with static storage duration with the |
| @code{__cxa_atexit} function rather than the @code{atexit} function. |
| This option is required for fully standards-compliant handling of static |
| destructors, but only works if your C library supports |
| @code{__cxa_atexit}. |
| |
| @item -fno-use-cxa-get-exception-ptr |
| @opindex fno-use-cxa-get-exception-ptr |
| Don't use the @code{__cxa_get_exception_ptr} runtime routine. This |
| causes @code{std::uncaught_exception} to be incorrect, but is necessary |
| if the runtime routine is not available. |
| |
| @item -fvisibility-inlines-hidden |
| @opindex fvisibility-inlines-hidden |
| This switch declares that the user does not attempt to compare |
| pointers to inline functions or methods where the addresses of the two functions |
| are taken in different shared objects. |
| |
| The effect of this is that GCC may, effectively, mark inline methods with |
| @code{__attribute__ ((visibility ("hidden")))} so that they do not |
| appear in the export table of a DSO and do not require a PLT indirection |
| when used within the DSO@. Enabling this option can have a dramatic effect |
| on load and link times of a DSO as it massively reduces the size of the |
| dynamic export table when the library makes heavy use of templates. |
| |
| The behavior of this switch is not quite the same as marking the |
| methods as hidden directly, because it does not affect static variables |
| local to the function or cause the compiler to deduce that |
| the function is defined in only one shared object. |
| |
| You may mark a method as having a visibility explicitly to negate the |
| effect of the switch for that method. For example, if you do want to |
| compare pointers to a particular inline method, you might mark it as |
| having default visibility. Marking the enclosing class with explicit |
| visibility has no effect. |
| |
| Explicitly instantiated inline methods are unaffected by this option |
| as their linkage might otherwise cross a shared library boundary. |
| @xref{Template Instantiation}. |
| |
| @item -fvisibility-ms-compat |
| @opindex fvisibility-ms-compat |
| This flag attempts to use visibility settings to make GCC's C++ |
| linkage model compatible with that of Microsoft Visual Studio. |
| |
| The flag makes these changes to GCC's linkage model: |
| |
| @enumerate |
| @item |
| It sets the default visibility to @code{hidden}, like |
| @option{-fvisibility=hidden}. |
| |
| @item |
| Types, but not their members, are not hidden by default. |
| |
| @item |
| The One Definition Rule is relaxed for types without explicit |
| visibility specifications that are defined in more than one |
| shared object: those declarations are permitted if they are |
| permitted when this option is not used. |
| @end enumerate |
| |
| In new code it is better to use @option{-fvisibility=hidden} and |
| export those classes that are intended to be externally visible. |
| Unfortunately it is possible for code to rely, perhaps accidentally, |
| on the Visual Studio behavior. |
| |
| Among the consequences of these changes are that static data members |
| of the same type with the same name but defined in different shared |
| objects are different, so changing one does not change the other; |
| and that pointers to function members defined in different shared |
| objects may not compare equal. When this flag is given, it is a |
| violation of the ODR to define types with the same name differently. |
| |
| @item -fno-weak |
| @opindex fno-weak |
| Do not use weak symbol support, even if it is provided by the linker. |
| By default, G++ uses weak symbols if they are available. This |
| option exists only for testing, and should not be used by end-users; |
| it results in inferior code and has no benefits. This option may |
| be removed in a future release of G++. |
| |
| @item -nostdinc++ |
| @opindex nostdinc++ |
| Do not search for header files in the standard directories specific to |
| C++, but do still search the other standard directories. (This option |
| is used when building the C++ library.) |
| @end table |
| |
| In addition, these optimization, warning, and code generation options |
| have meanings only for C++ programs: |
| |
| @table @gcctabopt |
| @item -fno-default-inline |
| @opindex fno-default-inline |
| Do not assume @samp{inline} for functions defined inside a class scope. |
| @xref{Optimize Options,,Options That Control Optimization}. Note that these |
| functions have linkage like inline functions; they just aren't |
| inlined by default. |
| |
| @item -Wabi @r{(C, Objective-C, C++ and Objective-C++ only)} |
| @opindex Wabi |
| @opindex Wno-abi |
| Warn when G++ generates code that is probably not compatible with the |
| vendor-neutral C++ ABI@. Although an effort has been made to warn about |
| all such cases, there are probably some cases that are not warned about, |
| even though G++ is generating incompatible code. There may also be |
| cases where warnings are emitted even though the code that is generated |
| is compatible. |
| |
| You should rewrite your code to avoid these warnings if you are |
| concerned about the fact that code generated by G++ may not be binary |
| compatible with code generated by other compilers. |
| |
| The known incompatibilities in @option{-fabi-version=2} (the default) include: |
| |
| @itemize @bullet |
| |
| @item |
| A template with a non-type template parameter of reference type is |
| mangled incorrectly: |
| @smallexample |
| extern int N; |
| template <int &> struct S @{@}; |
| void n (S<N>) @{2@} |
| @end smallexample |
| |
| This is fixed in @option{-fabi-version=3}. |
| |
| @item |
| SIMD vector types declared using @code{__attribute ((vector_size))} are |
| mangled in a non-standard way that does not allow for overloading of |
| functions taking vectors of different sizes. |
| |
| The mangling is changed in @option{-fabi-version=4}. |
| @end itemize |
| |
| The known incompatibilities in @option{-fabi-version=1} include: |
| |
| @itemize @bullet |
| |
| @item |
| Incorrect handling of tail-padding for bit-fields. G++ may attempt to |
| pack data into the same byte as a base class. For example: |
| |
| @smallexample |
| struct A @{ virtual void f(); int f1 : 1; @}; |
| struct B : public A @{ int f2 : 1; @}; |
| @end smallexample |
| |
| @noindent |
| In this case, G++ places @code{B::f2} into the same byte |
| as @code{A::f1}; other compilers do not. You can avoid this problem |
| by explicitly padding @code{A} so that its size is a multiple of the |
| byte size on your platform; that causes G++ and other compilers to |
| lay out @code{B} identically. |
| |
| @item |
| Incorrect handling of tail-padding for virtual bases. G++ does not use |
| tail padding when laying out virtual bases. For example: |
| |
| @smallexample |
| struct A @{ virtual void f(); char c1; @}; |
| struct B @{ B(); char c2; @}; |
| struct C : public A, public virtual B @{@}; |
| @end smallexample |
| |
| @noindent |
| In this case, G++ does not place @code{B} into the tail-padding for |
| @code{A}; other compilers do. You can avoid this problem by |
| explicitly padding @code{A} so that its size is a multiple of its |
| alignment (ignoring virtual base classes); that causes G++ and other |
| compilers to lay out @code{C} identically. |
| |
| @item |
| Incorrect handling of bit-fields with declared widths greater than that |
| of their underlying types, when the bit-fields appear in a union. For |
| example: |
| |
| @smallexample |
| union U @{ int i : 4096; @}; |
| @end smallexample |
| |
| @noindent |
| Assuming that an @code{int} does not have 4096 bits, G++ makes the |
| union too small by the number of bits in an @code{int}. |
| |
| @item |
| Empty classes can be placed at incorrect offsets. For example: |
| |
| @smallexample |
| struct A @{@}; |
| |
| struct B @{ |
| A a; |
| virtual void f (); |
| @}; |
| |
| struct C : public B, public A @{@}; |
| @end smallexample |
| |
| @noindent |
| G++ places the @code{A} base class of @code{C} at a nonzero offset; |
| it should be placed at offset zero. G++ mistakenly believes that the |
| @code{A} data member of @code{B} is already at offset zero. |
| |
| @item |
| Names of template functions whose types involve @code{typename} or |
| template template parameters can be mangled incorrectly. |
| |
| @smallexample |
| template <typename Q> |
| void f(typename Q::X) @{@} |
| |
| template <template <typename> class Q> |
| void f(typename Q<int>::X) @{@} |
| @end smallexample |
| |
| @noindent |
| Instantiations of these templates may be mangled incorrectly. |
| |
| @end itemize |
| |
| It also warns about psABI-related changes. The known psABI changes at this |
| point include: |
| |
| @itemize @bullet |
| |
| @item |
| For SysV/x86-64, unions with @code{long double} members are |
| passed in memory as specified in psABI. For example: |
| |
| @smallexample |
| union U @{ |
| long double ld; |
| int i; |
| @}; |
| @end smallexample |
| |
| @noindent |
| @code{union U} is always passed in memory. |
| |
| @end itemize |
| |
| @item -Wctor-dtor-privacy @r{(C++ and Objective-C++ only)} |
| @opindex Wctor-dtor-privacy |
| @opindex Wno-ctor-dtor-privacy |
| Warn when a class seems unusable because all the constructors or |
| destructors in that class are private, and it has neither friends nor |
| public static member functions. |
| |
| @item -Wdelete-non-virtual-dtor @r{(C++ and Objective-C++ only)} |
| @opindex Wdelete-non-virtual-dtor |
| @opindex Wno-delete-non-virtual-dtor |
| Warn when @samp{delete} is used to destroy an instance of a class that |
| has virtual functions and non-virtual destructor. It is unsafe to delete |
| an instance of a derived class through a pointer to a base class if the |
| base class does not have a virtual destructor. This warning is enabled |
| by @option{-Wall}. |
| |
| @item -Wliteral-suffix @r{(C++ and Objective-C++ only)} |
| @opindex Wliteral-suffix |
| @opindex Wno-literal-suffix |
| Warn when a string or character literal is followed by a ud-suffix which does |
| not begin with an underscore. As a conforming extension, GCC treats such |
| suffixes as separate preprocessing tokens in order to maintain backwards |
| compatibility with code that uses formatting macros from @code{<inttypes.h>}. |
| For example: |
| |
| @smallexample |
| #define __STDC_FORMAT_MACROS |
| #include <inttypes.h> |
| #include <stdio.h> |
| |
| int main() @{ |
| int64_t i64 = 123; |
| printf("My int64: %"PRId64"\n", i64); |
| @} |
| @end smallexample |
| |
| In this case, @code{PRId64} is treated as a separate preprocessing token. |
| |
| This warning is enabled by default. |
| |
| @item -Wnarrowing @r{(C++ and Objective-C++ only)} |
| @opindex Wnarrowing |
| @opindex Wno-narrowing |
| Warn when a narrowing conversion prohibited by C++11 occurs within |
| @samp{@{ @}}, e.g. |
| |
| @smallexample |
| int i = @{ 2.2 @}; // error: narrowing from double to int |
| @end smallexample |
| |
| This flag is included in @option{-Wall} and @option{-Wc++11-compat}. |
| |
| With @option{-std=c++11}, @option{-Wno-narrowing} suppresses the diagnostic |
| required by the standard. Note that this does not affect the meaning |
| of well-formed code; narrowing conversions are still considered |
| ill-formed in SFINAE context. |
| |
| @item -Wnoexcept @r{(C++ and Objective-C++ only)} |
| @opindex Wnoexcept |
| @opindex Wno-noexcept |
| Warn when a noexcept-expression evaluates to false because of a call |
| to a function that does not have a non-throwing exception |
| specification (i.e. @samp{throw()} or @samp{noexcept}) but is known by |
| the compiler to never throw an exception. |
| |
| @item -Wnon-virtual-dtor @r{(C++ and Objective-C++ only)} |
| @opindex Wnon-virtual-dtor |
| @opindex Wno-non-virtual-dtor |
| Warn when a class has virtual functions and an accessible non-virtual |
| destructor, in which case it is possible but unsafe to delete |
| an instance of a derived class through a pointer to the base class. |
| This warning is also enabled if @option{-Weffc++} is specified. |
| |
| @item -Wreorder @r{(C++ and Objective-C++ only)} |
| @opindex Wreorder |
| @opindex Wno-reorder |
| @cindex reordering, warning |
| @cindex warning for reordering of member initializers |
| Warn when the order of member initializers given in the code does not |
| match the order in which they must be executed. For instance: |
| |
| @smallexample |
| struct A @{ |
| int i; |
| int j; |
| A(): j (0), i (1) @{ @} |
| @}; |
| @end smallexample |
| |
| @noindent |
| The compiler rearranges the member initializers for @samp{i} |
| and @samp{j} to match the declaration order of the members, emitting |
| a warning to that effect. This warning is enabled by @option{-Wall}. |
| @end table |
| |
| The following @option{-W@dots{}} options are not affected by @option{-Wall}. |
| |
| @table @gcctabopt |
| @item -Weffc++ @r{(C++ and Objective-C++ only)} |
| @opindex Weffc++ |
| @opindex Wno-effc++ |
| Warn about violations of the following style guidelines from Scott Meyers' |
| @cite{Effective C++, Second Edition} book: |
| |
| @itemize @bullet |
| @item |
| Item 11: Define a copy constructor and an assignment operator for classes |
| with dynamically-allocated memory. |
| |
| @item |
| Item 12: Prefer initialization to assignment in constructors. |
| |
| @item |
| Item 14: Make destructors virtual in base classes. |
| |
| @item |
| Item 15: Have @code{operator=} return a reference to @code{*this}. |
| |
| @item |
| Item 23: Don't try to return a reference when you must return an object. |
| |
| @end itemize |
| |
| Also warn about violations of the following style guidelines from |
| Scott Meyers' @cite{More Effective C++} book: |
| |
| @itemize @bullet |
| @item |
| Item 6: Distinguish between prefix and postfix forms of increment and |
| decrement operators. |
| |
| @item |
| Item 7: Never overload @code{&&}, @code{||}, or @code{,}. |
| |
| @end itemize |
| |
| When selecting this option, be aware that the standard library |
| headers do not obey all of these guidelines; use @samp{grep -v} |
| to filter out those warnings. |
| |
| @item -Wstrict-null-sentinel @r{(C++ and Objective-C++ only)} |
| @opindex Wstrict-null-sentinel |
| @opindex Wno-strict-null-sentinel |
| Warn about the use of an uncasted @code{NULL} as sentinel. When |
| compiling only with GCC this is a valid sentinel, as @code{NULL} is defined |
| to @code{__null}. Although it is a null pointer constant rather than a |
| null pointer, it is guaranteed to be of the same size as a pointer. |
| But this use is not portable across different compilers. |
| |
| @item -Wno-non-template-friend @r{(C++ and Objective-C++ only)} |
| @opindex Wno-non-template-friend |
| @opindex Wnon-template-friend |
| Disable warnings when non-templatized friend functions are declared |
| within a template. Since the advent of explicit template specification |
| support in G++, if the name of the friend is an unqualified-id (i.e., |
| @samp{friend foo(int)}), the C++ language specification demands that the |
| friend declare or define an ordinary, nontemplate function. (Section |
| 14.5.3). Before G++ implemented explicit specification, unqualified-ids |
| could be interpreted as a particular specialization of a templatized |
| function. Because this non-conforming behavior is no longer the default |
| behavior for G++, @option{-Wnon-template-friend} allows the compiler to |
| check existing code for potential trouble spots and is on by default. |
| This new compiler behavior can be turned off with |
| @option{-Wno-non-template-friend}, which keeps the conformant compiler code |
| but disables the helpful warning. |
| |
| @item -Wold-style-cast @r{(C++ and Objective-C++ only)} |
| @opindex Wold-style-cast |
| @opindex Wno-old-style-cast |
| Warn if an old-style (C-style) cast to a non-void type is used within |
| a C++ program. The new-style casts (@samp{dynamic_cast}, |
| @samp{static_cast}, @samp{reinterpret_cast}, and @samp{const_cast}) are |
| less vulnerable to unintended effects and much easier to search for. |
| |
| @item -Woverloaded-virtual @r{(C++ and Objective-C++ only)} |
| @opindex Woverloaded-virtual |
| @opindex Wno-overloaded-virtual |
| @cindex overloaded virtual function, warning |
| @cindex warning for overloaded virtual function |
| Warn when a function declaration hides virtual functions from a |
| base class. For example, in: |
| |
| @smallexample |
| struct A @{ |
| virtual void f(); |
| @}; |
| |
| struct B: public A @{ |
| void f(int); |
| @}; |
| @end smallexample |
| |
| the @code{A} class version of @code{f} is hidden in @code{B}, and code |
| like: |
| |
| @smallexample |
| B* b; |
| b->f(); |
| @end smallexample |
| |
| @noindent |
| fails to compile. |
| |
| @item -Wno-pmf-conversions @r{(C++ and Objective-C++ only)} |
| @opindex Wno-pmf-conversions |
| @opindex Wpmf-conversions |
| Disable the diagnostic for converting a bound pointer to member function |
| to a plain pointer. |
| |
| @item -Wsign-promo @r{(C++ and Objective-C++ only)} |
| @opindex Wsign-promo |
| @opindex Wno-sign-promo |
| Warn when overload resolution chooses a promotion from unsigned or |
| enumerated type to a signed type, over a conversion to an unsigned type of |
| the same size. Previous versions of G++ tried to preserve |
| unsignedness, but the standard mandates the current behavior. |
| |
| @smallexample |
| struct A @{ |
| operator int (); |
| A& operator = (int); |
| @}; |
| |
| main () |
| @{ |
| A a,b; |
| a = b; |
| @} |
| @end smallexample |
| |
| @noindent |
| In this example, G++ synthesizes a default @samp{A& operator = |
| (const A&);}, while cfront uses the user-defined @samp{operator =}. |
| @end table |
| |
| @node Objective-C and Objective-C++ Dialect Options |
| @section Options Controlling Objective-C and Objective-C++ Dialects |
| |
| @cindex compiler options, Objective-C and Objective-C++ |
| @cindex Objective-C and Objective-C++ options, command-line |
| @cindex options, Objective-C and Objective-C++ |
| (NOTE: This manual does not describe the Objective-C and Objective-C++ |
| languages themselves. @xref{Standards,,Language Standards |
| Supported by GCC}, for references.) |
| |
| This section describes the command-line options that are only meaningful |
| for Objective-C and Objective-C++ programs. You can also use most of |
| the language-independent GNU compiler options. |
| For example, you might compile a file @code{some_class.m} like this: |
| |
| @smallexample |
| gcc -g -fgnu-runtime -O -c some_class.m |
| @end smallexample |
| |
| @noindent |
| In this example, @option{-fgnu-runtime} is an option meant only for |
| Objective-C and Objective-C++ programs; you can use the other options with |
| any language supported by GCC@. |
| |
| Note that since Objective-C is an extension of the C language, Objective-C |
| compilations may also use options specific to the C front-end (e.g., |
| @option{-Wtraditional}). Similarly, Objective-C++ compilations may use |
| C++-specific options (e.g., @option{-Wabi}). |
| |
| Here is a list of options that are @emph{only} for compiling Objective-C |
| and Objective-C++ programs: |
| |
| @table @gcctabopt |
| @item -fconstant-string-class=@var{class-name} |
| @opindex fconstant-string-class |
| Use @var{class-name} as the name of the class to instantiate for each |
| literal string specified with the syntax @code{@@"@dots{}"}. The default |
| class name is @code{NXConstantString} if the GNU runtime is being used, and |
| @code{NSConstantString} if the NeXT runtime is being used (see below). The |
| @option{-fconstant-cfstrings} option, if also present, overrides the |
| @option{-fconstant-string-class} setting and cause @code{@@"@dots{}"} literals |
| to be laid out as constant CoreFoundation strings. |
| |
| @item -fgnu-runtime |
| @opindex fgnu-runtime |
| Generate object code compatible with the standard GNU Objective-C |
| runtime. This is the default for most types of systems. |
| |
| @item -fnext-runtime |
| @opindex fnext-runtime |
| Generate output compatible with the NeXT runtime. This is the default |
| for NeXT-based systems, including Darwin and Mac OS X@. The macro |
| @code{__NEXT_RUNTIME__} is predefined if (and only if) this option is |
| used. |
| |
| @item -fno-nil-receivers |
| @opindex fno-nil-receivers |
| Assume that all Objective-C message dispatches (@code{[receiver |
| message:arg]}) in this translation unit ensure that the receiver is |
| not @code{nil}. This allows for more efficient entry points in the |
| runtime to be used. This option is only available in conjunction with |
| the NeXT runtime and ABI version 0 or 1. |
| |
| @item -fobjc-abi-version=@var{n} |
| @opindex fobjc-abi-version |
| Use version @var{n} of the Objective-C ABI for the selected runtime. |
| This option is currently supported only for the NeXT runtime. In that |
| case, Version 0 is the traditional (32-bit) ABI without support for |
| properties and other Objective-C 2.0 additions. Version 1 is the |
| traditional (32-bit) ABI with support for properties and other |
| Objective-C 2.0 additions. Version 2 is the modern (64-bit) ABI. If |
| nothing is specified, the default is Version 0 on 32-bit target |
| machines, and Version 2 on 64-bit target machines. |
| |
| @item -fobjc-call-cxx-cdtors |
| @opindex fobjc-call-cxx-cdtors |
| For each Objective-C class, check if any of its instance variables is a |
| C++ object with a non-trivial default constructor. If so, synthesize a |
| special @code{- (id) .cxx_construct} instance method which runs |
| non-trivial default constructors on any such instance variables, in order, |
| and then return @code{self}. Similarly, check if any instance variable |
| is a C++ object with a non-trivial destructor, and if so, synthesize a |
| special @code{- (void) .cxx_destruct} method which runs |
| all such default destructors, in reverse order. |
| |
| The @code{- (id) .cxx_construct} and @code{- (void) .cxx_destruct} |
| methods thusly generated only operate on instance variables |
| declared in the current Objective-C class, and not those inherited |
| from superclasses. It is the responsibility of the Objective-C |
| runtime to invoke all such methods in an object's inheritance |
| hierarchy. The @code{- (id) .cxx_construct} methods are invoked |
| by the runtime immediately after a new object instance is allocated; |
| the @code{- (void) .cxx_destruct} methods are invoked immediately |
| before the runtime deallocates an object instance. |
| |
| As of this writing, only the NeXT runtime on Mac OS X 10.4 and later has |
| support for invoking the @code{- (id) .cxx_construct} and |
| @code{- (void) .cxx_destruct} methods. |
| |
| @item -fobjc-direct-dispatch |
| @opindex fobjc-direct-dispatch |
| Allow fast jumps to the message dispatcher. On Darwin this is |
| accomplished via the comm page. |
| |
| @item -fobjc-exceptions |
| @opindex fobjc-exceptions |
| Enable syntactic support for structured exception handling in |
| Objective-C, similar to what is offered by C++ and Java. This option |
| is required to use the Objective-C keywords @code{@@try}, |
| @code{@@throw}, @code{@@catch}, @code{@@finally} and |
| @code{@@synchronized}. This option is available with both the GNU |
| runtime and the NeXT runtime (but not available in conjunction with |
| the NeXT runtime on Mac OS X 10.2 and earlier). |
| |
| @item -fobjc-gc |
| @opindex fobjc-gc |
| Enable garbage collection (GC) in Objective-C and Objective-C++ |
| programs. This option is only available with the NeXT runtime; the |
| GNU runtime has a different garbage collection implementation that |
| does not require special compiler flags. |
| |
| @item -fobjc-nilcheck |
| @opindex fobjc-nilcheck |
| For the NeXT runtime with version 2 of the ABI, check for a nil |
| receiver in method invocations before doing the actual method call. |
| This is the default and can be disabled using |
| @option{-fno-objc-nilcheck}. Class methods and super calls are never |
| checked for nil in this way no matter what this flag is set to. |
| Currently this flag does nothing when the GNU runtime, or an older |
| version of the NeXT runtime ABI, is used. |
| |
| @item -fobjc-std=objc1 |
| @opindex fobjc-std |
| Conform to the language syntax of Objective-C 1.0, the language |
| recognized by GCC 4.0. This only affects the Objective-C additions to |
| the C/C++ language; it does not affect conformance to C/C++ standards, |
| which is controlled by the separate C/C++ dialect option flags. When |
| this option is used with the Objective-C or Objective-C++ compiler, |
| any Objective-C syntax that is not recognized by GCC 4.0 is rejected. |
| This is useful if you need to make sure that your Objective-C code can |
| be compiled with older versions of GCC@. |
| |
| @item -freplace-objc-classes |
| @opindex freplace-objc-classes |
| Emit a special marker instructing @command{ld(1)} not to statically link in |
| the resulting object file, and allow @command{dyld(1)} to load it in at |
| run time instead. This is used in conjunction with the Fix-and-Continue |
| debugging mode, where the object file in question may be recompiled and |
| dynamically reloaded in the course of program execution, without the need |
| to restart the program itself. Currently, Fix-and-Continue functionality |
| is only available in conjunction with the NeXT runtime on Mac OS X 10.3 |
| and later. |
| |
| @item -fzero-link |
| @opindex fzero-link |
| When compiling for the NeXT runtime, the compiler ordinarily replaces calls |
| to @code{objc_getClass("@dots{}")} (when the name of the class is known at |
| compile time) with static class references that get initialized at load time, |
| which improves run-time performance. Specifying the @option{-fzero-link} flag |
| suppresses this behavior and causes calls to @code{objc_getClass("@dots{}")} |
| to be retained. This is useful in Zero-Link debugging mode, since it allows |
| for individual class implementations to be modified during program execution. |
| The GNU runtime currently always retains calls to @code{objc_get_class("@dots{}")} |
| regardless of command-line options. |
| |
| @item -gen-decls |
| @opindex gen-decls |
| Dump interface declarations for all classes seen in the source file to a |
| file named @file{@var{sourcename}.decl}. |
| |
| @item -Wassign-intercept @r{(Objective-C and Objective-C++ only)} |
| @opindex Wassign-intercept |
| @opindex Wno-assign-intercept |
| Warn whenever an Objective-C assignment is being intercepted by the |
| garbage collector. |
| |
| @item -Wno-protocol @r{(Objective-C and Objective-C++ only)} |
| @opindex Wno-protocol |
| @opindex Wprotocol |
| If a class is declared to implement a protocol, a warning is issued for |
| every method in the protocol that is not implemented by the class. The |
| default behavior is to issue a warning for every method not explicitly |
| implemented in the class, even if a method implementation is inherited |
| from the superclass. If you use the @option{-Wno-protocol} option, then |
| methods inherited from the superclass are considered to be implemented, |
| and no warning is issued for them. |
| |
| @item -Wselector @r{(Objective-C and Objective-C++ only)} |
| @opindex Wselector |
| @opindex Wno-selector |
| Warn if multiple methods of different types for the same selector are |
| found during compilation. The check is performed on the list of methods |
| in the final stage of compilation. Additionally, a check is performed |
| for each selector appearing in a @code{@@selector(@dots{})} |
| expression, and a corresponding method for that selector has been found |
| during compilation. Because these checks scan the method table only at |
| the end of compilation, these warnings are not produced if the final |
| stage of compilation is not reached, for example because an error is |
| found during compilation, or because the @option{-fsyntax-only} option is |
| being used. |
| |
| @item -Wstrict-selector-match @r{(Objective-C and Objective-C++ only)} |
| @opindex Wstrict-selector-match |
| @opindex Wno-strict-selector-match |
| Warn if multiple methods with differing argument and/or return types are |
| found for a given selector when attempting to send a message using this |
| selector to a receiver of type @code{id} or @code{Class}. When this flag |
| is off (which is the default behavior), the compiler omits such warnings |
| if any differences found are confined to types that share the same size |
| and alignment. |
| |
| @item -Wundeclared-selector @r{(Objective-C and Objective-C++ only)} |
| @opindex Wundeclared-selector |
| @opindex Wno-undeclared-selector |
| Warn if a @code{@@selector(@dots{})} expression referring to an |
| undeclared selector is found. A selector is considered undeclared if no |
| method with that name has been declared before the |
| @code{@@selector(@dots{})} expression, either explicitly in an |
| @code{@@interface} or @code{@@protocol} declaration, or implicitly in |
| an @code{@@implementation} section. This option always performs its |
| checks as soon as a @code{@@selector(@dots{})} expression is found, |
| while @option{-Wselector} only performs its checks in the final stage of |
| compilation. This also enforces the coding style convention |
| that methods and selectors must be declared before being used. |
| |
| @item -print-objc-runtime-info |
| @opindex print-objc-runtime-info |
| Generate C header describing the largest structure that is passed by |
| value, if any. |
| |
| @end table |
| |
| @node Language Independent Options |
| @section Options to Control Diagnostic Messages Formatting |
| @cindex options to control diagnostics formatting |
| @cindex diagnostic messages |
| @cindex message formatting |
| |
| Traditionally, diagnostic messages have been formatted irrespective of |
| the output device's aspect (e.g.@: its width, @dots{}). You can use the |
| options described below |
| to control the formatting algorithm for diagnostic messages, |
| e.g.@: how many characters per line, how often source location |
| information should be reported. Note that some language front ends may not |
| honor these options. |
| |
| @table @gcctabopt |
| @item -fmessage-length=@var{n} |
| @opindex fmessage-length |
| Try to format error messages so that they fit on lines of about @var{n} |
| characters. The default is 72 characters for @command{g++} and 0 for the rest of |
| the front ends supported by GCC@. If @var{n} is zero, then no |
| line-wrapping is done; each error message appears on a single |
| line. |
| |
| @item -fdiagnostics-show-location=once |
| @opindex fdiagnostics-show-location |
| Only meaningful in line-wrapping mode. Instructs the diagnostic messages |
| reporter to emit source location information @emph{once}; that is, in |
| case the message is too long to fit on a single physical line and has to |
| be wrapped, the source location won't be emitted (as prefix) again, |
| over and over, in subsequent continuation lines. This is the default |
| behavior. |
| |
| @item -fdiagnostics-show-location=every-line |
| Only meaningful in line-wrapping mode. Instructs the diagnostic |
| messages reporter to emit the same source location information (as |
| prefix) for physical lines that result from the process of breaking |
| a message which is too long to fit on a single line. |
| |
| @item -fno-diagnostics-show-option |
| @opindex fno-diagnostics-show-option |
| @opindex fdiagnostics-show-option |
| By default, each diagnostic emitted includes text indicating the |
| command-line option that directly controls the diagnostic (if such an |
| option is known to the diagnostic machinery). Specifying the |
| @option{-fno-diagnostics-show-option} flag suppresses that behavior. |
| |
| @item -fno-diagnostics-show-caret |
| @opindex fno-diagnostics-show-caret |
| @opindex fdiagnostics-show-caret |
| By default, each diagnostic emitted includes the original source line |
| and a caret '^' indicating the column. This option suppresses this |
| information. |
| |
| @end table |
| |
| @node Warning Options |
| @section Options to Request or Suppress Warnings |
| @cindex options to control warnings |
| @cindex warning messages |
| @cindex messages, warning |
| @cindex suppressing warnings |
| |
| Warnings are diagnostic messages that report constructions that |
| are not inherently erroneous but that are risky or suggest there |
| may have been an error. |
| |
| The following language-independent options do not enable specific |
| warnings but control the kinds of diagnostics produced by GCC@. |
| |
| @table @gcctabopt |
| @cindex syntax checking |
| @item -fsyntax-only |
| @opindex fsyntax-only |
| Check the code for syntax errors, but don't do anything beyond that. |
| |
| @item -fmax-errors=@var{n} |
| @opindex fmax-errors |
| Limits the maximum number of error messages to @var{n}, at which point |
| GCC bails out rather than attempting to continue processing the source |
| code. If @var{n} is 0 (the default), there is no limit on the number |
| of error messages produced. If @option{-Wfatal-errors} is also |
| specified, then @option{-Wfatal-errors} takes precedence over this |
| option. |
| |
| @item -w |
| @opindex w |
| Inhibit all warning messages. |
| |
| @item -Werror |
| @opindex Werror |
| @opindex Wno-error |
| Make all warnings into errors. |
| |
| @item -Werror= |
| @opindex Werror= |
| @opindex Wno-error= |
| Make the specified warning into an error. The specifier for a warning |
| is appended; for example @option{-Werror=switch} turns the warnings |
| controlled by @option{-Wswitch} into errors. This switch takes a |
| negative form, to be used to negate @option{-Werror} for specific |
| warnings; for example @option{-Wno-error=switch} makes |
| @option{-Wswitch} warnings not be errors, even when @option{-Werror} |
| is in effect. |
| |
| The warning message for each controllable warning includes the |
| option that controls the warning. That option can then be used with |
| @option{-Werror=} and @option{-Wno-error=} as described above. |
| (Printing of the option in the warning message can be disabled using the |
| @option{-fno-diagnostics-show-option} flag.) |
| |
| Note that specifying @option{-Werror=}@var{foo} automatically implies |
| @option{-W}@var{foo}. However, @option{-Wno-error=}@var{foo} does not |
| imply anything. |
| |
| @item -Wfatal-errors |
| @opindex Wfatal-errors |
| @opindex Wno-fatal-errors |
| This option causes the compiler to abort compilation on the first error |
| occurred rather than trying to keep going and printing further error |
| messages. |
| |
| @end table |
| |
| You can request many specific warnings with options beginning with |
| @samp{-W}, for example @option{-Wimplicit} to request warnings on |
| implicit declarations. Each of these specific warning options also |
| has a negative form beginning @samp{-Wno-} to turn off warnings; for |
| example, @option{-Wno-implicit}. This manual lists only one of the |
| two forms, whichever is not the default. For further |
| language-specific options also refer to @ref{C++ Dialect Options} and |
| @ref{Objective-C and Objective-C++ Dialect Options}. |
| |
| When an unrecognized warning option is requested (e.g., |
| @option{-Wunknown-warning}), GCC emits a diagnostic stating |
| that the option is not recognized. However, if the @option{-Wno-} form |
| is used, the behavior is slightly different: no diagnostic is |
| produced for @option{-Wno-unknown-warning} unless other diagnostics |
| are being produced. This allows the use of new @option{-Wno-} options |
| with old compilers, but if something goes wrong, the compiler |
| warns that an unrecognized option is present. |
| |
| @table @gcctabopt |
| @item -Wpedantic |
| @itemx -pedantic |
| @opindex pedantic |
| @opindex Wpedantic |
| Issue all the warnings demanded by strict ISO C and ISO C++; |
| reject all programs that use forbidden extensions, and some other |
| programs that do not follow ISO C and ISO C++. For ISO C, follows the |
| version of the ISO C standard specified by any @option{-std} option used. |
| |
| Valid ISO C and ISO C++ programs should compile properly with or without |
| this option (though a rare few require @option{-ansi} or a |
| @option{-std} option specifying the required version of ISO C)@. However, |
| without this option, certain GNU extensions and traditional C and C++ |
| features are supported as well. With this option, they are rejected. |
| |
| @option{-Wpedantic} does not cause warning messages for use of the |
| alternate keywords whose names begin and end with @samp{__}. Pedantic |
| warnings are also disabled in the expression that follows |
| @code{__extension__}. However, only system header files should use |
| these escape routes; application programs should avoid them. |
| @xref{Alternate Keywords}. |
| |
| Some users try to use @option{-Wpedantic} to check programs for strict ISO |
| C conformance. They soon find that it does not do quite what they want: |
| it finds some non-ISO practices, but not all---only those for which |
| ISO C @emph{requires} a diagnostic, and some others for which |
| diagnostics have been added. |
| |
| A feature to report any failure to conform to ISO C might be useful in |
| some instances, but would require considerable additional work and would |
| be quite different from @option{-Wpedantic}. We don't have plans to |
| support such a feature in the near future. |
| |
| Where the standard specified with @option{-std} represents a GNU |
| extended dialect of C, such as @samp{gnu90} or @samp{gnu99}, there is a |
| corresponding @dfn{base standard}, the version of ISO C on which the GNU |
| extended dialect is based. Warnings from @option{-Wpedantic} are given |
| where they are required by the base standard. (It does not make sense |
| for such warnings to be given only for features not in the specified GNU |
| C dialect, since by definition the GNU dialects of C include all |
| features the compiler supports with the given option, and there would be |
| nothing to warn about.) |
| |
| @item -pedantic-errors |
| @opindex pedantic-errors |
| Like @option{-Wpedantic}, except that errors are produced rather than |
| warnings. |
| |
| @item -Wall |
| @opindex Wall |
| @opindex Wno-all |
| This enables all the warnings about constructions that some users |
| consider questionable, and that are easy to avoid (or modify to |
| prevent the warning), even in conjunction with macros. This also |
| enables some language-specific warnings described in @ref{C++ Dialect |
| Options} and @ref{Objective-C and Objective-C++ Dialect Options}. |
| |
| @option{-Wall} turns on the following warning flags: |
| |
| @gccoptlist{-Waddress @gol |
| -Warray-bounds @r{(only with} @option{-O2}@r{)} @gol |
| -Wc++11-compat @gol |
| -Wchar-subscripts @gol |
| -Wenum-compare @r{(in C/ObjC; this is on by default in C++)} @gol |
| -Wimplicit-int @r{(C and Objective-C only)} @gol |
| -Wimplicit-function-declaration @r{(C and Objective-C only)} @gol |
| -Wcomment @gol |
| -Wformat @gol |
| -Wmain @r{(only for C/ObjC and unless} @option{-ffreestanding}@r{)} @gol |
| -Wmaybe-uninitialized @gol |
| -Wmissing-braces @r{(only for C/ObjC)} @gol |
| -Wnonnull @gol |
| -Wparentheses @gol |
| -Wpointer-sign @gol |
| -Wreorder @gol |
| -Wreturn-type @gol |
| -Wsequence-point @gol |
| -Wsign-compare @r{(only in C++)} @gol |
| -Wstrict-aliasing @gol |
| -Wstrict-overflow=1 @gol |
| -Wswitch @gol |
| -Wtrigraphs @gol |
| -Wuninitialized @gol |
| -Wunknown-pragmas @gol |
| -Wunused-function @gol |
| -Wunused-label @gol |
| -Wunused-value @gol |
| -Wunused-variable @gol |
| -Wvolatile-register-var @gol |
| } |
| |
| Note that some warning flags are not implied by @option{-Wall}. Some of |
| them warn about constructions that users generally do not consider |
| questionable, but which occasionally you might wish to check for; |
| others warn about constructions that are necessary or hard to avoid in |
| some cases, and there is no simple way to modify the code to suppress |
| the warning. Some of them are enabled by @option{-Wextra} but many of |
| them must be enabled individually. |
| |
| @item -Wextra |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| This enables some extra warning flags that are not enabled by |
| @option{-Wall}. (This option used to be called @option{-W}. The older |
| name is still supported, but the newer name is more descriptive.) |
| |
| @gccoptlist{-Wclobbered @gol |
| -Wempty-body @gol |
| -Wignored-qualifiers @gol |
| -Wmissing-field-initializers @gol |
| -Wmissing-parameter-type @r{(C only)} @gol |
| -Wold-style-declaration @r{(C only)} @gol |
| -Woverride-init @gol |
| -Wsign-compare @gol |
| -Wtype-limits @gol |
| -Wuninitialized @gol |
| -Wunused-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol |
| -Wunused-but-set-parameter @r{(only with} @option{-Wunused} @r{or} @option{-Wall}@r{)} @gol |
| } |
| |
| The option @option{-Wextra} also prints warning messages for the |
| following cases: |
| |
| @itemize @bullet |
| |
| @item |
| A pointer is compared against integer zero with @samp{<}, @samp{<=}, |
| @samp{>}, or @samp{>=}. |
| |
| @item |
| (C++ only) An enumerator and a non-enumerator both appear in a |
| conditional expression. |
| |
| @item |
| (C++ only) Ambiguous virtual bases. |
| |
| @item |
| (C++ only) Subscripting an array that has been declared @samp{register}. |
| |
| @item |
| (C++ only) Taking the address of a variable that has been declared |
| @samp{register}. |
| |
| @item |
| (C++ only) A base class is not initialized in a derived class's copy |
| constructor. |
| |
| @end itemize |
| |
| @item -Wchar-subscripts |
| @opindex Wchar-subscripts |
| @opindex Wno-char-subscripts |
| Warn if an array subscript has type @code{char}. This is a common cause |
| of error, as programmers often forget that this type is signed on some |
| machines. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wcomment |
| @opindex Wcomment |
| @opindex Wno-comment |
| Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*} |
| comment, or whenever a Backslash-Newline appears in a @samp{//} comment. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-coverage-mismatch |
| @opindex Wno-coverage-mismatch |
| Warn if feedback profiles do not match when using the |
| @option{-fprofile-use} option. |
| If a source file is changed between compiling with @option{-fprofile-gen} and |
| with @option{-fprofile-use}, the files with the profile feedback can fail |
| to match the source file and GCC cannot use the profile feedback |
| information. By default, this warning is enabled and is treated as an |
| error. @option{-Wno-coverage-mismatch} can be used to disable the |
| warning or @option{-Wno-error=coverage-mismatch} can be used to |
| disable the error. Disabling the error for this warning can result in |
| poorly optimized code and is useful only in the |
| case of very minor changes such as bug fixes to an existing code-base. |
| Completely disabling the warning is not recommended. |
| |
| @item -Wno-cpp |
| @r{(C, Objective-C, C++, Objective-C++ and Fortran only)} |
| |
| Suppress warning messages emitted by @code{#warning} directives. |
| |
| @item -Wdouble-promotion @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Wdouble-promotion |
| @opindex Wno-double-promotion |
| Give a warning when a value of type @code{float} is implicitly |
| promoted to @code{double}. CPUs with a 32-bit ``single-precision'' |
| floating-point unit implement @code{float} in hardware, but emulate |
| @code{double} in software. On such a machine, doing computations |
| using @code{double} values is much more expensive because of the |
| overhead required for software emulation. |
| |
| It is easy to accidentally do computations with @code{double} because |
| floating-point literals are implicitly of type @code{double}. For |
| example, in: |
| @smallexample |
| @group |
| float area(float radius) |
| @{ |
| return 3.14159 * radius * radius; |
| @} |
| @end group |
| @end smallexample |
| the compiler performs the entire computation with @code{double} |
| because the floating-point literal is a @code{double}. |
| |
| @item -Wformat |
| @opindex Wformat |
| @opindex Wno-format |
| @opindex ffreestanding |
| @opindex fno-builtin |
| Check calls to @code{printf} and @code{scanf}, etc., to make sure that |
| the arguments supplied have types appropriate to the format string |
| specified, and that the conversions specified in the format string make |
| sense. This includes standard functions, and others specified by format |
| attributes (@pxref{Function Attributes}), in the @code{printf}, |
| @code{scanf}, @code{strftime} and @code{strfmon} (an X/Open extension, |
| not in the C standard) families (or other target-specific families). |
| Which functions are checked without format attributes having been |
| specified depends on the standard version selected, and such checks of |
| functions without the attribute specified are disabled by |
| @option{-ffreestanding} or @option{-fno-builtin}. |
| |
| The formats are checked against the format features supported by GNU |
| libc version 2.2. These include all ISO C90 and C99 features, as well |
| as features from the Single Unix Specification and some BSD and GNU |
| extensions. Other library implementations may not support all these |
| features; GCC does not support warning about features that go beyond a |
| particular library's limitations. However, if @option{-Wpedantic} is used |
| with @option{-Wformat}, warnings are given about format features not |
| in the selected standard version (but not for @code{strfmon} formats, |
| since those are not in any version of the C standard). @xref{C Dialect |
| Options,,Options Controlling C Dialect}. |
| |
| Since @option{-Wformat} also checks for null format arguments for |
| several functions, @option{-Wformat} also implies @option{-Wnonnull}. |
| |
| @option{-Wformat} is included in @option{-Wall}. For more control over some |
| aspects of format checking, the options @option{-Wformat-y2k}, |
| @option{-Wno-format-extra-args}, @option{-Wno-format-zero-length}, |
| @option{-Wformat-nonliteral}, @option{-Wformat-security}, and |
| @option{-Wformat=2} are available, but are not included in @option{-Wall}. |
| |
| @item -Wformat-y2k |
| @opindex Wformat-y2k |
| @opindex Wno-format-y2k |
| If @option{-Wformat} is specified, also warn about @code{strftime} |
| formats that may yield only a two-digit year. |
| |
| @item -Wno-format-contains-nul |
| @opindex Wno-format-contains-nul |
| @opindex Wformat-contains-nul |
| If @option{-Wformat} is specified, do not warn about format strings that |
| contain NUL bytes. |
| |
| @item -Wno-format-extra-args |
| @opindex Wno-format-extra-args |
| @opindex Wformat-extra-args |
| If @option{-Wformat} is specified, do not warn about excess arguments to a |
| @code{printf} or @code{scanf} format function. The C standard specifies |
| that such arguments are ignored. |
| |
| Where the unused arguments lie between used arguments that are |
| specified with @samp{$} operand number specifications, normally |
| warnings are still given, since the implementation could not know what |
| type to pass to @code{va_arg} to skip the unused arguments. However, |
| in the case of @code{scanf} formats, this option suppresses the |
| warning if the unused arguments are all pointers, since the Single |
| Unix Specification says that such unused arguments are allowed. |
| |
| @item -Wno-format-zero-length |
| @opindex Wno-format-zero-length |
| @opindex Wformat-zero-length |
| If @option{-Wformat} is specified, do not warn about zero-length formats. |
| The C standard specifies that zero-length formats are allowed. |
| |
| @item -Wformat-nonliteral |
| @opindex Wformat-nonliteral |
| @opindex Wno-format-nonliteral |
| If @option{-Wformat} is specified, also warn if the format string is not a |
| string literal and so cannot be checked, unless the format function |
| takes its format arguments as a @code{va_list}. |
| |
| @item -Wformat-security |
| @opindex Wformat-security |
| @opindex Wno-format-security |
| If @option{-Wformat} is specified, also warn about uses of format |
| functions that represent possible security problems. At present, this |
| warns about calls to @code{printf} and @code{scanf} functions where the |
| format string is not a string literal and there are no format arguments, |
| as in @code{printf (foo);}. This may be a security hole if the format |
| string came from untrusted input and contains @samp{%n}. (This is |
| currently a subset of what @option{-Wformat-nonliteral} warns about, but |
| in future warnings may be added to @option{-Wformat-security} that are not |
| included in @option{-Wformat-nonliteral}.) |
| |
| @item -Wformat=2 |
| @opindex Wformat=2 |
| @opindex Wno-format=2 |
| Enable @option{-Wformat} plus format checks not included in |
| @option{-Wformat}. Currently equivalent to @option{-Wformat |
| -Wformat-nonliteral -Wformat-security -Wformat-y2k}. |
| |
| @item -Wnonnull |
| @opindex Wnonnull |
| @opindex Wno-nonnull |
| Warn about passing a null pointer for arguments marked as |
| requiring a non-null value by the @code{nonnull} function attribute. |
| |
| @option{-Wnonnull} is included in @option{-Wall} and @option{-Wformat}. It |
| can be disabled with the @option{-Wno-nonnull} option. |
| |
| @item -Winit-self @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Winit-self |
| @opindex Wno-init-self |
| Warn about uninitialized variables that are initialized with themselves. |
| Note this option can only be used with the @option{-Wuninitialized} option. |
| |
| For example, GCC warns about @code{i} being uninitialized in the |
| following snippet only when @option{-Winit-self} has been specified: |
| @smallexample |
| @group |
| int f() |
| @{ |
| int i = i; |
| return i; |
| @} |
| @end group |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall} in C++. |
| |
| @item -Wimplicit-int @r{(C and Objective-C only)} |
| @opindex Wimplicit-int |
| @opindex Wno-implicit-int |
| Warn when a declaration does not specify a type. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wimplicit-function-declaration @r{(C and Objective-C only)} |
| @opindex Wimplicit-function-declaration |
| @opindex Wno-implicit-function-declaration |
| Give a warning whenever a function is used before being declared. In |
| C99 mode (@option{-std=c99} or @option{-std=gnu99}), this warning is |
| enabled by default and it is made into an error by |
| @option{-pedantic-errors}. This warning is also enabled by |
| @option{-Wall}. |
| |
| @item -Wimplicit @r{(C and Objective-C only)} |
| @opindex Wimplicit |
| @opindex Wno-implicit |
| Same as @option{-Wimplicit-int} and @option{-Wimplicit-function-declaration}. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wignored-qualifiers @r{(C and C++ only)} |
| @opindex Wignored-qualifiers |
| @opindex Wno-ignored-qualifiers |
| Warn if the return type of a function has a type qualifier |
| such as @code{const}. For ISO C such a type qualifier has no effect, |
| since the value returned by a function is not an lvalue. |
| For C++, the warning is only emitted for scalar types or @code{void}. |
| ISO C prohibits qualified @code{void} return types on function |
| definitions, so such return types always receive a warning |
| even without this option. |
| |
| This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wmain |
| @opindex Wmain |
| @opindex Wno-main |
| Warn if the type of @samp{main} is suspicious. @samp{main} should be |
| a function with external linkage, returning int, taking either zero |
| arguments, two, or three arguments of appropriate types. This warning |
| is enabled by default in C++ and is enabled by either @option{-Wall} |
| or @option{-Wpedantic}. |
| |
| @item -Wmissing-braces |
| @opindex Wmissing-braces |
| @opindex Wno-missing-braces |
| Warn if an aggregate or union initializer is not fully bracketed. In |
| the following example, the initializer for @samp{a} is not fully |
| bracketed, but that for @samp{b} is fully bracketed. This warning is |
| enabled by @option{-Wall} in C. |
| |
| @smallexample |
| int a[2][2] = @{ 0, 1, 2, 3 @}; |
| int b[2][2] = @{ @{ 0, 1 @}, @{ 2, 3 @} @}; |
| @end smallexample |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wmissing-include-dirs @r{(C, C++, Objective-C and Objective-C++ only)} |
| @opindex Wmissing-include-dirs |
| @opindex Wno-missing-include-dirs |
| Warn if a user-supplied include directory does not exist. |
| |
| @item -Wparentheses |
| @opindex Wparentheses |
| @opindex Wno-parentheses |
| Warn if parentheses are omitted in certain contexts, such |
| as when there is an assignment in a context where a truth value |
| is expected, or when operators are nested whose precedence people |
| often get confused about. |
| |
| Also warn if a comparison like @samp{x<=y<=z} appears; this is |
| equivalent to @samp{(x<=y ? 1 : 0) <= z}, which is a different |
| interpretation from that of ordinary mathematical notation. |
| |
| Also warn about constructions where there may be confusion to which |
| @code{if} statement an @code{else} branch belongs. Here is an example of |
| such a case: |
| |
| @smallexample |
| @group |
| @{ |
| if (a) |
| if (b) |
| foo (); |
| else |
| bar (); |
| @} |
| @end group |
| @end smallexample |
| |
| In C/C++, every @code{else} branch belongs to the innermost possible |
| @code{if} statement, which in this example is @code{if (b)}. This is |
| often not what the programmer expected, as illustrated in the above |
| example by indentation the programmer chose. When there is the |
| potential for this confusion, GCC issues a warning when this flag |
| is specified. To eliminate the warning, add explicit braces around |
| the innermost @code{if} statement so there is no way the @code{else} |
| can belong to the enclosing @code{if}. The resulting code |
| looks like this: |
| |
| @smallexample |
| @group |
| @{ |
| if (a) |
| @{ |
| if (b) |
| foo (); |
| else |
| bar (); |
| @} |
| @} |
| @end group |
| @end smallexample |
| |
| Also warn for dangerous uses of the GNU extension to |
| @code{?:} with omitted middle operand. When the condition |
| in the @code{?}: operator is a boolean expression, the omitted value is |
| always 1. Often programmers expect it to be a value computed |
| inside the conditional expression instead. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wsequence-point |
| @opindex Wsequence-point |
| @opindex Wno-sequence-point |
| Warn about code that may have undefined semantics because of violations |
| of sequence point rules in the C and C++ standards. |
| |
| The C and C++ standards define the order in which expressions in a C/C++ |
| program are evaluated in terms of @dfn{sequence points}, which represent |
| a partial ordering between the execution of parts of the program: those |
| executed before the sequence point, and those executed after it. These |
| occur after the evaluation of a full expression (one which is not part |
| of a larger expression), after the evaluation of the first operand of a |
| @code{&&}, @code{||}, @code{? :} or @code{,} (comma) operator, before a |
| function is called (but after the evaluation of its arguments and the |
| expression denoting the called function), and in certain other places. |
| Other than as expressed by the sequence point rules, the order of |
| evaluation of subexpressions of an expression is not specified. All |
| these rules describe only a partial order rather than a total order, |
| since, for example, if two functions are called within one expression |
| with no sequence point between them, the order in which the functions |
| are called is not specified. However, the standards committee have |
| ruled that function calls do not overlap. |
| |
| It is not specified when between sequence points modifications to the |
| values of objects take effect. Programs whose behavior depends on this |
| have undefined behavior; the C and C++ standards specify that ``Between |
| the previous and next sequence point an object shall have its stored |
| value modified at most once by the evaluation of an expression. |
| Furthermore, the prior value shall be read only to determine the value |
| to be stored.''. If a program breaks these rules, the results on any |
| particular implementation are entirely unpredictable. |
| |
| Examples of code with undefined behavior are @code{a = a++;}, @code{a[n] |
| = b[n++]} and @code{a[i++] = i;}. Some more complicated cases are not |
| diagnosed by this option, and it may give an occasional false positive |
| result, but in general it has been found fairly effective at detecting |
| this sort of problem in programs. |
| |
| The standard is worded confusingly, therefore there is some debate |
| over the precise meaning of the sequence point rules in subtle cases. |
| Links to discussions of the problem, including proposed formal |
| definitions, may be found on the GCC readings page, at |
| @uref{http://gcc.gnu.org/@/readings.html}. |
| |
| This warning is enabled by @option{-Wall} for C and C++. |
| |
| @item -Wreturn-type |
| @opindex Wreturn-type |
| @opindex Wno-return-type |
| Warn whenever a function is defined with a return type that defaults |
| to @code{int}. Also warn about any @code{return} statement with no |
| return value in a function whose return type is not @code{void} |
| (falling off the end of the function body is considered returning |
| without a value), and about a @code{return} statement with an |
| expression in a function whose return type is @code{void}. |
| |
| For C++, a function without return type always produces a diagnostic |
| message, even when @option{-Wno-return-type} is specified. The only |
| exceptions are @samp{main} and functions defined in system headers. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wswitch |
| @opindex Wswitch |
| @opindex Wno-switch |
| Warn whenever a @code{switch} statement has an index of enumerated type |
| and lacks a @code{case} for one or more of the named codes of that |
| enumeration. (The presence of a @code{default} label prevents this |
| warning.) @code{case} labels outside the enumeration range also |
| provoke warnings when this option is used (even if there is a |
| @code{default} label). |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wswitch-default |
| @opindex Wswitch-default |
| @opindex Wno-switch-default |
| Warn whenever a @code{switch} statement does not have a @code{default} |
| case. |
| |
| @item -Wswitch-enum |
| @opindex Wswitch-enum |
| @opindex Wno-switch-enum |
| Warn whenever a @code{switch} statement has an index of enumerated type |
| and lacks a @code{case} for one or more of the named codes of that |
| enumeration. @code{case} labels outside the enumeration range also |
| provoke warnings when this option is used. The only difference |
| between @option{-Wswitch} and this option is that this option gives a |
| warning about an omitted enumeration code even if there is a |
| @code{default} label. |
| |
| @item -Wsync-nand @r{(C and C++ only)} |
| @opindex Wsync-nand |
| @opindex Wno-sync-nand |
| Warn when @code{__sync_fetch_and_nand} and @code{__sync_nand_and_fetch} |
| built-in functions are used. These functions changed semantics in GCC 4.4. |
| |
| @item -Wtrigraphs |
| @opindex Wtrigraphs |
| @opindex Wno-trigraphs |
| Warn if any trigraphs are encountered that might change the meaning of |
| the program (trigraphs within comments are not warned about). |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused-but-set-parameter |
| @opindex Wunused-but-set-parameter |
| @opindex Wno-unused-but-set-parameter |
| Warn whenever a function parameter is assigned to, but otherwise unused |
| (aside from its declaration). |
| |
| To suppress this warning use the @samp{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| This warning is also enabled by @option{-Wunused} together with |
| @option{-Wextra}. |
| |
| @item -Wunused-but-set-variable |
| @opindex Wunused-but-set-variable |
| @opindex Wno-unused-but-set-variable |
| Warn whenever a local variable is assigned to, but otherwise unused |
| (aside from its declaration). |
| This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @samp{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| This warning is also enabled by @option{-Wunused}, which is enabled |
| by @option{-Wall}. |
| |
| @item -Wunused-function |
| @opindex Wunused-function |
| @opindex Wno-unused-function |
| Warn whenever a static function is declared but not defined or a |
| non-inline static function is unused. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused-label |
| @opindex Wunused-label |
| @opindex Wno-unused-label |
| Warn whenever a label is declared but not used. |
| This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @samp{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wunused-local-typedefs @r{(C, Objective-C, C++ and Objective-C++ only)} |
| @opindex Wunused-local-typedefs |
| Warn when a typedef locally defined in a function is not used. |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused-parameter |
| @opindex Wunused-parameter |
| @opindex Wno-unused-parameter |
| Warn whenever a function parameter is unused aside from its declaration. |
| |
| To suppress this warning use the @samp{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wno-unused-result |
| @opindex Wunused-result |
| @opindex Wno-unused-result |
| Do not warn if a caller of a function marked with attribute |
| @code{warn_unused_result} (@pxref{Function Attributes}) does not use |
| its return value. The default is @option{-Wunused-result}. |
| |
| @item -Wunused-variable |
| @opindex Wunused-variable |
| @opindex Wno-unused-variable |
| Warn whenever a local variable or non-constant static variable is unused |
| aside from its declaration. |
| This warning is enabled by @option{-Wall}. |
| |
| To suppress this warning use the @samp{unused} attribute |
| (@pxref{Variable Attributes}). |
| |
| @item -Wunused-value |
| @opindex Wunused-value |
| @opindex Wno-unused-value |
| Warn whenever a statement computes a result that is explicitly not |
| used. To suppress this warning cast the unused expression to |
| @samp{void}. This includes an expression-statement or the left-hand |
| side of a comma expression that contains no side effects. For example, |
| an expression such as @samp{x[i,j]} causes a warning, while |
| @samp{x[(void)i,j]} does not. |
| |
| This warning is enabled by @option{-Wall}. |
| |
| @item -Wunused |
| @opindex Wunused |
| @opindex Wno-unused |
| All the above @option{-Wunused} options combined. |
| |
| In order to get a warning about an unused function parameter, you must |
| either specify @option{-Wextra -Wunused} (note that @option{-Wall} implies |
| @option{-Wunused}), or separately specify @option{-Wunused-parameter}. |
| |
| @item -Wuninitialized |
| @opindex Wuninitialized |
| @opindex Wno-uninitialized |
| Warn if an automatic variable is used without first being initialized |
| or if a variable may be clobbered by a @code{setjmp} call. In C++, |
| warn if a non-static reference or non-static @samp{const} member |
| appears in a class without constructors. |
| |
| If you want to warn about code that uses the uninitialized value of the |
| variable in its own initializer, use the @option{-Winit-self} option. |
| |
| These warnings occur for individual uninitialized or clobbered |
| elements of structure, union or array variables as well as for |
| variables that are uninitialized or clobbered as a whole. They do |
| not occur for variables or elements declared @code{volatile}. Because |
| these warnings depend on optimization, the exact variables or elements |
| for which there are warnings depends on the precise optimization |
| options and version of GCC used. |
| |
| Note that there may be no warning about a variable that is used only |
| to compute a value that itself is never used, because such |
| computations may be deleted by data flow analysis before the warnings |
| are printed. |
| |
| @item -Wmaybe-uninitialized |
| @opindex Wmaybe-uninitialized |
| @opindex Wno-maybe-uninitialized |
| For an automatic variable, if there exists a path from the function |
| entry to a use of the variable that is initialized, but there exist |
| some other paths for which the variable is not initialized, the compiler |
| emits a warning if it cannot prove the uninitialized paths are not |
| executed at run time. These warnings are made optional because GCC is |
| not smart enough to see all the reasons why the code might be correct |
| in spite of appearing to have an error. Here is one example of how |
| this can happen: |
| |
| @smallexample |
| @group |
| @{ |
| int x; |
| switch (y) |
| @{ |
| case 1: x = 1; |
| break; |
| case 2: x = 4; |
| break; |
| case 3: x = 5; |
| @} |
| foo (x); |
| @} |
| @end group |
| @end smallexample |
| |
| @noindent |
| If the value of @code{y} is always 1, 2 or 3, then @code{x} is |
| always initialized, but GCC doesn't know this. To suppress the |
| warning, you need to provide a default case with assert(0) or |
| similar code. |
| |
| @cindex @code{longjmp} warnings |
| This option also warns when a non-volatile automatic variable might be |
| changed by a call to @code{longjmp}. These warnings as well are possible |
| only in optimizing compilation. |
| |
| The compiler sees only the calls to @code{setjmp}. It cannot know |
| where @code{longjmp} will be called; in fact, a signal handler could |
| call it at any point in the code. As a result, you may get a warning |
| even when there is in fact no problem because @code{longjmp} cannot |
| in fact be called at the place that would cause a problem. |
| |
| Some spurious warnings can be avoided if you declare all the functions |
| you use that never return as @code{noreturn}. @xref{Function |
| Attributes}. |
| |
| This warning is enabled by @option{-Wall} or @option{-Wextra}. |
| |
| @item -Wunknown-pragmas |
| @opindex Wunknown-pragmas |
| @opindex Wno-unknown-pragmas |
| @cindex warning for unknown pragmas |
| @cindex unknown pragmas, warning |
| @cindex pragmas, warning of unknown |
| Warn when a @code{#pragma} directive is encountered that is not understood by |
| GCC@. If this command-line option is used, warnings are even issued |
| for unknown pragmas in system header files. This is not the case if |
| the warnings are only enabled by the @option{-Wall} command-line option. |
| |
| @item -Wno-pragmas |
| @opindex Wno-pragmas |
| @opindex Wpragmas |
| Do not warn about misuses of pragmas, such as incorrect parameters, |
| invalid syntax, or conflicts between pragmas. See also |
| @option{-Wunknown-pragmas}. |
| |
| @item -Wstrict-aliasing |
| @opindex Wstrict-aliasing |
| @opindex Wno-strict-aliasing |
| This option is only active when @option{-fstrict-aliasing} is active. |
| It warns about code that might break the strict aliasing rules that the |
| compiler is using for optimization. The warning does not catch all |
| cases, but does attempt to catch the more common pitfalls. It is |
| included in @option{-Wall}. |
| It is equivalent to @option{-Wstrict-aliasing=3} |
| |
| @item -Wstrict-aliasing=n |
| @opindex Wstrict-aliasing=n |
| @opindex Wno-strict-aliasing=n |
| This option is only active when @option{-fstrict-aliasing} is active. |
| It warns about code that might break the strict aliasing rules that the |
| compiler is using for optimization. |
| Higher levels correspond to higher accuracy (fewer false positives). |
| Higher levels also correspond to more effort, similar to the way @option{-O} |
| works. |
| @option{-Wstrict-aliasing} is equivalent to @option{-Wstrict-aliasing=3}. |
| |
| Level 1: Most aggressive, quick, least accurate. |
| Possibly useful when higher levels |
| do not warn but @option{-fstrict-aliasing} still breaks the code, as it has very few |
| false negatives. However, it has many false positives. |
| Warns for all pointer conversions between possibly incompatible types, |
| even if never dereferenced. Runs in the front end only. |
| |
| Level 2: Aggressive, quick, not too precise. |
| May still have many false positives (not as many as level 1 though), |
| and few false negatives (but possibly more than level 1). |
| Unlike level 1, it only warns when an address is taken. Warns about |
| incomplete types. Runs in the front end only. |
| |
| Level 3 (default for @option{-Wstrict-aliasing}): |
| Should have very few false positives and few false |
| negatives. Slightly slower than levels 1 or 2 when optimization is enabled. |
| Takes care of the common pun+dereference pattern in the front end: |
| @code{*(int*)&some_float}. |
| If optimization is enabled, it also runs in the back end, where it deals |
| with multiple statement cases using flow-sensitive points-to information. |
| Only warns when the converted pointer is dereferenced. |
| Does not warn about incomplete types. |
| |
| @item -Wstrict-overflow |
| @itemx -Wstrict-overflow=@var{n} |
| @opindex Wstrict-overflow |
| @opindex Wno-strict-overflow |
| This option is only active when @option{-fstrict-overflow} is active. |
| It warns about cases where the compiler optimizes based on the |
| assumption that signed overflow does not occur. Note that it does not |
| warn about all cases where the code might overflow: it only warns |
| about cases where the compiler implements some optimization. Thus |
| this warning depends on the optimization level. |
| |
| An optimization that assumes that signed overflow does not occur is |
| perfectly safe if the values of the variables involved are such that |
| overflow never does, in fact, occur. Therefore this warning can |
| easily give a false positive: a warning about code that is not |
| actually a problem. To help focus on important issues, several |
| warning levels are defined. No warnings are issued for the use of |
| undefined signed overflow when estimating how many iterations a loop |
| requires, in particular when determining whether a loop will be |
| executed at all. |
| |
| @table @gcctabopt |
| @item -Wstrict-overflow=1 |
| Warn about cases that are both questionable and easy to avoid. For |
| example, with @option{-fstrict-overflow}, the compiler simplifies |
| @code{x + 1 > x} to @code{1}. This level of |
| @option{-Wstrict-overflow} is enabled by @option{-Wall}; higher levels |
| are not, and must be explicitly requested. |
| |
| @item -Wstrict-overflow=2 |
| Also warn about other cases where a comparison is simplified to a |
| constant. For example: @code{abs (x) >= 0}. This can only be |
| simplified when @option{-fstrict-overflow} is in effect, because |
| @code{abs (INT_MIN)} overflows to @code{INT_MIN}, which is less than |
| zero. @option{-Wstrict-overflow} (with no level) is the same as |
| @option{-Wstrict-overflow=2}. |
| |
| @item -Wstrict-overflow=3 |
| Also warn about other cases where a comparison is simplified. For |
| example: @code{x + 1 > 1} is simplified to @code{x > 0}. |
| |
| @item -Wstrict-overflow=4 |
| Also warn about other simplifications not covered by the above cases. |
| For example: @code{(x * 10) / 5} is simplified to @code{x * 2}. |
| |
| @item -Wstrict-overflow=5 |
| Also warn about cases where the compiler reduces the magnitude of a |
| constant involved in a comparison. For example: @code{x + 2 > y} is |
| simplified to @code{x + 1 >= y}. This is reported only at the |
| highest warning level because this simplification applies to many |
| comparisons, so this warning level gives a very large number of |
| false positives. |
| @end table |
| |
| @item -Wsuggest-attribute=@r{[}pure@r{|}const@r{|}noreturn@r{|}format@r{]} |
| @opindex Wsuggest-attribute= |
| @opindex Wno-suggest-attribute= |
| Warn for cases where adding an attribute may be beneficial. The |
| attributes currently supported are listed below. |
| |
| @table @gcctabopt |
| @item -Wsuggest-attribute=pure |
| @itemx -Wsuggest-attribute=const |
| @itemx -Wsuggest-attribute=noreturn |
| @opindex Wsuggest-attribute=pure |
| @opindex Wno-suggest-attribute=pure |
| @opindex Wsuggest-attribute=const |
| @opindex Wno-suggest-attribute=const |
| @opindex Wsuggest-attribute=noreturn |
| @opindex Wno-suggest-attribute=noreturn |
| |
| Warn about functions that might be candidates for attributes |
| @code{pure}, @code{const} or @code{noreturn}. The compiler only warns for |
| functions visible in other compilation units or (in the case of @code{pure} and |
| @code{const}) if it cannot prove that the function returns normally. A function |
| returns normally if it doesn't contain an infinite loop or return abnormally |
| by throwing, calling @code{abort()} or trapping. This analysis requires option |
| @option{-fipa-pure-const}, which is enabled by default at @option{-O} and |
| higher. Higher optimization levels improve the accuracy of the analysis. |
| |
| @item -Wsuggest-attribute=format |
| @itemx -Wmissing-format-attribute |
| @opindex Wsuggest-attribute=format |
| @opindex Wmissing-format-attribute |
| @opindex Wno-suggest-attribute=format |
| @opindex Wno-missing-format-attribute |
| @opindex Wformat |
| @opindex Wno-format |
| |
| Warn about function pointers that might be candidates for @code{format} |
| attributes. Note these are only possible candidates, not absolute ones. |
| GCC guesses that function pointers with @code{format} attributes that |
| are used in assignment, initialization, parameter passing or return |
| statements should have a corresponding @code{format} attribute in the |
| resulting type. I.e.@: the left-hand side of the assignment or |
| initialization, the type of the parameter variable, or the return type |
| of the containing function respectively should also have a @code{format} |
| attribute to avoid the warning. |
| |
| GCC also warns about function definitions that might be |
| candidates for @code{format} attributes. Again, these are only |
| possible candidates. GCC guesses that @code{format} attributes |
| might be appropriate for any function that calls a function like |
| @code{vprintf} or @code{vscanf}, but this might not always be the |
| case, and some functions for which @code{format} attributes are |
| appropriate may not be detected. |
| @end table |
| |
| @item -Warray-bounds |
| @opindex Wno-array-bounds |
| @opindex Warray-bounds |
| This option is only active when @option{-ftree-vrp} is active |
| (default for @option{-O2} and above). It warns about subscripts to arrays |
| that are always out of bounds. This warning is enabled by @option{-Wall}. |
| |
| @item -Wno-div-by-zero |
| @opindex Wno-div-by-zero |
| @opindex Wdiv-by-zero |
| Do not warn about compile-time integer division by zero. Floating-point |
| division by zero is not warned about, as it can be a legitimate way of |
| obtaining infinities and NaNs. |
| |
| @item -Wsystem-headers |
| @opindex Wsystem-headers |
| @opindex Wno-system-headers |
| @cindex warnings from system headers |
| @cindex system headers, warnings from |
| Print warning messages for constructs found in system header files. |
| Warnings from system headers are normally suppressed, on the assumption |
| that they usually do not indicate real problems and would only make the |
| compiler output harder to read. Using this command-line option tells |
| GCC to emit warnings from system headers as if they occurred in user |
| code. However, note that using @option{-Wall} in conjunction with this |
| option does @emph{not} warn about unknown pragmas in system |
| headers---for that, @option{-Wunknown-pragmas} must also be used. |
| |
| @item -Wtrampolines |
| @opindex Wtrampolines |
| @opindex Wno-trampolines |
| Warn about trampolines generated for pointers to nested functions. |
| |
| A trampoline is a small piece of data or code that is created at run |
| time on the stack when the address of a nested function is taken, and |
| is used to call the nested function indirectly. For some targets, it |
| is made up of data only and thus requires no special treatment. But, |
| for most targets, it is made up of code and thus requires the stack |
| to be made executable in order for the program to work properly. |
| |
| @item -Wfloat-equal |
| @opindex Wfloat-equal |
| @opindex Wno-float-equal |
| Warn if floating-point values are used in equality comparisons. |
| |
| The idea behind this is that sometimes it is convenient (for the |
| programmer) to consider floating-point values as approximations to |
| infinitely precise real numbers. If you are doing this, then you need |
| to compute (by analyzing the code, or in some other way) the maximum or |
| likely maximum error that the computation introduces, and allow for it |
| when performing comparisons (and when producing output, but that's a |
| different problem). In particular, instead of testing for equality, you |
| should check to see whether the two values have ranges that overlap; and |
| this is done with the relational operators, so equality comparisons are |
| probably mistaken. |
| |
| @item -Wtraditional @r{(C and Objective-C only)} |
| @opindex Wtraditional |
| @opindex Wno-traditional |
| Warn about certain constructs that behave differently in traditional and |
| ISO C@. Also warn about ISO C constructs that have no traditional C |
| equivalent, and/or problematic constructs that should be avoided. |
| |
| @itemize @bullet |
| @item |
| Macro parameters that appear within string literals in the macro body. |
| In traditional C macro replacement takes place within string literals, |
| but in ISO C it does not. |
| |
| @item |
| In traditional C, some preprocessor directives did not exist. |
| Traditional preprocessors only considered a line to be a directive |
| if the @samp{#} appeared in column 1 on the line. Therefore |
| @option{-Wtraditional} warns about directives that traditional C |
| understands but ignores because the @samp{#} does not appear as the |
| first character on the line. It also suggests you hide directives like |
| @samp{#pragma} not understood by traditional C by indenting them. Some |
| traditional implementations do not recognize @samp{#elif}, so this option |
| suggests avoiding it altogether. |
| |
| @item |
| A function-like macro that appears without arguments. |
| |
| @item |
| The unary plus operator. |
| |
| @item |
| The @samp{U} integer constant suffix, or the @samp{F} or @samp{L} floating-point |
| constant suffixes. (Traditional C does support the @samp{L} suffix on integer |
| constants.) Note, these suffixes appear in macros defined in the system |
| headers of most modern systems, e.g.@: the @samp{_MIN}/@samp{_MAX} macros in @code{<limits.h>}. |
| Use of these macros in user code might normally lead to spurious |
| warnings, however GCC's integrated preprocessor has enough context to |
| avoid warning in these cases. |
| |
| @item |
| A function declared external in one block and then used after the end of |
| the block. |
| |
| @item |
| A @code{switch} statement has an operand of type @code{long}. |
| |
| @item |
| A non-@code{static} function declaration follows a @code{static} one. |
| This construct is not accepted by some traditional C compilers. |
| |
| @item |
| The ISO type of an integer constant has a different width or |
| signedness from its traditional type. This warning is only issued if |
| the base of the constant is ten. I.e.@: hexadecimal or octal values, which |
| typically represent bit patterns, are not warned about. |
| |
| @item |
| Usage of ISO string concatenation is detected. |
| |
| @item |
| Initialization of automatic aggregates. |
| |
| @item |
| Identifier conflicts with labels. Traditional C lacks a separate |
| namespace for labels. |
| |
| @item |
| Initialization of unions. If the initializer is zero, the warning is |
| omitted. This is done under the assumption that the zero initializer in |
| user code appears conditioned on e.g.@: @code{__STDC__} to avoid missing |
| initializer warnings and relies on default initialization to zero in the |
| traditional C case. |
| |
| @item |
| Conversions by prototypes between fixed/floating-point values and vice |
| versa. The absence of these prototypes when compiling with traditional |
| C causes serious problems. This is a subset of the possible |
| conversion warnings; for the full set use @option{-Wtraditional-conversion}. |
| |
| @item |
| Use of ISO C style function definitions. This warning intentionally is |
| @emph{not} issued for prototype declarations or variadic functions |
| because these ISO C features appear in your code when using |
| libiberty's traditional C compatibility macros, @code{PARAMS} and |
| @code{VPARAMS}. This warning is also bypassed for nested functions |
| because that feature is already a GCC extension and thus not relevant to |
| traditional C compatibility. |
| @end itemize |
| |
| @item -Wtraditional-conversion @r{(C and Objective-C only)} |
| @opindex Wtraditional-conversion |
| @opindex Wno-traditional-conversion |
| Warn if a prototype causes a type conversion that is different from what |
| would happen to the same argument in the absence of a prototype. This |
| includes conversions of fixed point to floating and vice versa, and |
| conversions changing the width or signedness of a fixed-point argument |
| except when the same as the default promotion. |
| |
| @item -Wdeclaration-after-statement @r{(C and Objective-C only)} |
| @opindex Wdeclaration-after-statement |
| @opindex Wno-declaration-after-statement |
| Warn when a declaration is found after a statement in a block. This |
| construct, known from C++, was introduced with ISO C99 and is by default |
| allowed in GCC@. It is not supported by ISO C90 and was not supported by |
| GCC versions before GCC 3.0. @xref{Mixed Declarations}. |
| |
| @item -Wundef |
| @opindex Wundef |
| @opindex Wno-undef |
| Warn if an undefined identifier is evaluated in an @samp{#if} directive. |
| |
| @item -Wno-endif-labels |
| @opindex Wno-endif-labels |
| @opindex Wendif-labels |
| Do not warn whenever an @samp{#else} or an @samp{#endif} are followed by text. |
| |
| @item -Wshadow |
| @opindex Wshadow |
| @opindex Wno-shadow |
| Warn whenever a local variable or type declaration shadows another variable, |
| parameter, type, or class member (in C++), or whenever a built-in function |
| is shadowed. Note that in C++, the compiler warns if a local variable |
| shadows an explicit typedef, but not if it shadows a struct/class/enum. |
| |
| @item -Wlarger-than=@var{len} |
| @opindex Wlarger-than=@var{len} |
| @opindex Wlarger-than-@var{len} |
| Warn whenever an object of larger than @var{len} bytes is defined. |
| |
| @item -Wframe-larger-than=@var{len} |
| @opindex Wframe-larger-than |
| Warn if the size of a function frame is larger than @var{len} bytes. |
| The computation done to determine the stack frame size is approximate |
| and not conservative. |
| The actual requirements may be somewhat greater than @var{len} |
| even if you do not get a warning. In addition, any space allocated |
| via @code{alloca}, variable-length arrays, or related constructs |
| is not included by the compiler when determining |
| whether or not to issue a warning. |
| |
| @item -Wno-free-nonheap-object |
| @opindex Wno-free-nonheap-object |
| @opindex Wfree-nonheap-object |
| Do not warn when attempting to free an object that was not allocated |
| on the heap. |
| |
| @item -Wstack-usage=@var{len} |
| @opindex Wstack-usage |
| Warn if the stack usage of a function might be larger than @var{len} bytes. |
| The computation done to determine the stack usage is conservative. |
| Any space allocated via @code{alloca}, variable-length arrays, or related |
| constructs is included by the compiler when determining whether or not to |
| issue a warning. |
| |
| The message is in keeping with the output of @option{-fstack-usage}. |
| |
| @itemize |
| @item |
| If the stack usage is fully static but exceeds the specified amount, it's: |
| |
| @smallexample |
| warning: stack usage is 1120 bytes |
| @end smallexample |
| @item |
| If the stack usage is (partly) dynamic but bounded, it's: |
| |
| @smallexample |
| warning: stack usage might be 1648 bytes |
| @end smallexample |
| @item |
| If the stack usage is (partly) dynamic and not bounded, it's: |
| |
| @smallexample |
| warning: stack usage might be unbounded |
| @end smallexample |
| @end itemize |
| |
| @item -Wunsafe-loop-optimizations |
| @opindex Wunsafe-loop-optimizations |
| @opindex Wno-unsafe-loop-optimizations |
| Warn if the loop cannot be optimized because the compiler cannot |
| assume anything on the bounds of the loop indices. With |
| @option{-funsafe-loop-optimizations} warn if the compiler makes |
| such assumptions. |
| |
| @item -Wno-pedantic-ms-format @r{(MinGW targets only)} |
| @opindex Wno-pedantic-ms-format |
| @opindex Wpedantic-ms-format |
| When used in combination with @option{-Wformat} |
| and @option{-pedantic} without GNU extensions, this option |
| disables the warnings about non-ISO @code{printf} / @code{scanf} format |
| width specifiers @code{I32}, @code{I64}, and @code{I} used on Windows targets, |
| which depend on the MS runtime. |
| |
| @item -Wpointer-arith |
| @opindex Wpointer-arith |
| @opindex Wno-pointer-arith |
| Warn about anything that depends on the ``size of'' a function type or |
| of @code{void}. GNU C assigns these types a size of 1, for |
| convenience in calculations with @code{void *} pointers and pointers |
| to functions. In C++, warn also when an arithmetic operation involves |
| @code{NULL}. This warning is also enabled by @option{-Wpedantic}. |
| |
| @item -Wtype-limits |
| @opindex Wtype-limits |
| @opindex Wno-type-limits |
| Warn if a comparison is always true or always false due to the limited |
| range of the data type, but do not warn for constant expressions. For |
| example, warn if an unsigned variable is compared against zero with |
| @samp{<} or @samp{>=}. This warning is also enabled by |
| @option{-Wextra}. |
| |
| @item -Wbad-function-cast @r{(C and Objective-C only)} |
| @opindex Wbad-function-cast |
| @opindex Wno-bad-function-cast |
| Warn whenever a function call is cast to a non-matching type. |
| For example, warn if @code{int malloc()} is cast to @code{anything *}. |
| |
| @item -Wc++-compat @r{(C and Objective-C only)} |
| Warn about ISO C constructs that are outside of the common subset of |
| ISO C and ISO C++, e.g.@: request for implicit conversion from |
| @code{void *} to a pointer to non-@code{void} type. |
| |
| @item -Wc++11-compat @r{(C++ and Objective-C++ only)} |
| Warn about C++ constructs whose meaning differs between ISO C++ 1998 |
| and ISO C++ 2011, e.g., identifiers in ISO C++ 1998 that are keywords |
| in ISO C++ 2011. This warning turns on @option{-Wnarrowing} and is |
| enabled by @option{-Wall}. |
| |
| @item -Wcast-qual |
| @opindex Wcast-qual |
| @opindex Wno-cast-qual |
| Warn whenever a pointer is cast so as to remove a type qualifier from |
| the target type. For example, warn if a @code{const char *} is cast |
| to an ordinary @code{char *}. |
| |
| Also warn when making a cast that introduces a type qualifier in an |
| unsafe way. For example, casting @code{char **} to @code{const char **} |
| is unsafe, as in this example: |
| |
| @smallexample |
| /* p is char ** value. */ |
| const char **q = (const char **) p; |
| /* Assignment of readonly string to const char * is OK. */ |
| *q = "string"; |
| /* Now char** pointer points to read-only memory. */ |
| **p = 'b'; |
| @end smallexample |
| |
| @item -Wcast-align |
| @opindex Wcast-align |
| @opindex Wno-cast-align |
| Warn whenever a pointer is cast such that the required alignment of the |
| target is increased. For example, warn if a @code{char *} is cast to |
| an @code{int *} on machines where integers can only be accessed at |
| two- or four-byte boundaries. |
| |
| @item -Wwrite-strings |
| @opindex Wwrite-strings |
| @opindex Wno-write-strings |
| When compiling C, give string constants the type @code{const |
| char[@var{length}]} so that copying the address of one into a |
| non-@code{const} @code{char *} pointer produces a warning. These |
| warnings help you find at compile time code that can try to write |
| into a string constant, but only if you have been very careful about |
| using @code{const} in declarations and prototypes. Otherwise, it is |
| just a nuisance. This is why we did not make @option{-Wall} request |
| these warnings. |
| |
| When compiling C++, warn about the deprecated conversion from string |
| literals to @code{char *}. This warning is enabled by default for C++ |
| programs. |
| |
| @item -Wclobbered |
| @opindex Wclobbered |
| @opindex Wno-clobbered |
| Warn for variables that might be changed by @samp{longjmp} or |
| @samp{vfork}. This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wconversion |
| @opindex Wconversion |
| @opindex Wno-conversion |
| Warn for implicit conversions that may alter a value. This includes |
| conversions between real and integer, like @code{abs (x)} when |
| @code{x} is @code{double}; conversions between signed and unsigned, |
| like @code{unsigned ui = -1}; and conversions to smaller types, like |
| @code{sqrtf (M_PI)}. Do not warn for explicit casts like @code{abs |
| ((int) x)} and @code{ui = (unsigned) -1}, or if the value is not |
| changed by the conversion like in @code{abs (2.0)}. Warnings about |
| conversions between signed and unsigned integers can be disabled by |
| using @option{-Wno-sign-conversion}. |
| |
| For C++, also warn for confusing overload resolution for user-defined |
| conversions; and conversions that never use a type conversion |
| operator: conversions to @code{void}, the same type, a base class or a |
| reference to them. Warnings about conversions between signed and |
| unsigned integers are disabled by default in C++ unless |
| @option{-Wsign-conversion} is explicitly enabled. |
| |
| @item -Wno-conversion-null @r{(C++ and Objective-C++ only)} |
| @opindex Wconversion-null |
| @opindex Wno-conversion-null |
| Do not warn for conversions between @code{NULL} and non-pointer |
| types. @option{-Wconversion-null} is enabled by default. |
| |
| @item -Wzero-as-null-pointer-constant @r{(C++ and Objective-C++ only)} |
| @opindex Wzero-as-null-pointer-constant |
| @opindex Wno-zero-as-null-pointer-constant |
| Warn when a literal '0' is used as null pointer constant. This can |
| be useful to facilitate the conversion to @code{nullptr} in C++11. |
| |
| @item -Wuseless-cast @r{(C++ and Objective-C++ only)} |
| @opindex Wuseless-cast |
| @opindex Wno-useless-cast |
| Warn when an expression is casted to its own type. |
| |
| @item -Wempty-body |
| @opindex Wempty-body |
| @opindex Wno-empty-body |
| Warn if an empty body occurs in an @samp{if}, @samp{else} or @samp{do |
| while} statement. This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wenum-compare |
| @opindex Wenum-compare |
| @opindex Wno-enum-compare |
| Warn about a comparison between values of different enumerated types. |
| In C++ enumeral mismatches in conditional expressions are also |
| diagnosed and the warning is enabled by default. In C this warning is |
| enabled by @option{-Wall}. |
| |
| @item -Wjump-misses-init @r{(C, Objective-C only)} |
| @opindex Wjump-misses-init |
| @opindex Wno-jump-misses-init |
| Warn if a @code{goto} statement or a @code{switch} statement jumps |
| forward across the initialization of a variable, or jumps backward to a |
| label after the variable has been initialized. This only warns about |
| variables that are initialized when they are declared. This warning is |
| only supported for C and Objective-C; in C++ this sort of branch is an |
| error in any case. |
| |
| @option{-Wjump-misses-init} is included in @option{-Wc++-compat}. It |
| can be disabled with the @option{-Wno-jump-misses-init} option. |
| |
| @item -Wsign-compare |
| @opindex Wsign-compare |
| @opindex Wno-sign-compare |
| @cindex warning for comparison of signed and unsigned values |
| @cindex comparison of signed and unsigned values, warning |
| @cindex signed and unsigned values, comparison warning |
| Warn when a comparison between signed and unsigned values could produce |
| an incorrect result when the signed value is converted to unsigned. |
| This warning is also enabled by @option{-Wextra}; to get the other warnings |
| of @option{-Wextra} without this warning, use @option{-Wextra -Wno-sign-compare}. |
| |
| @item -Wsign-conversion |
| @opindex Wsign-conversion |
| @opindex Wno-sign-conversion |
| Warn for implicit conversions that may change the sign of an integer |
| value, like assigning a signed integer expression to an unsigned |
| integer variable. An explicit cast silences the warning. In C, this |
| option is enabled also by @option{-Wconversion}. |
| |
| @item -Wsizeof-pointer-memaccess |
| @opindex Wsizeof-pointer-memaccess |
| @opindex Wno-sizeof-pointer-memaccess |
| Warn for suspicious length parameters to certain string and memory built-in |
| functions if the argument uses @code{sizeof}. This warning warns e.g.@: |
| about @code{memset (ptr, 0, sizeof (ptr));} if @code{ptr} is not an array, |
| but a pointer, and suggests a possible fix, or about |
| @code{memcpy (&foo, ptr, sizeof (&foo));}. This warning is enabled by |
| @option{-Wall}. |
| |
| @item -Waddress |
| @opindex Waddress |
| @opindex Wno-address |
| Warn about suspicious uses of memory addresses. These include using |
| the address of a function in a conditional expression, such as |
| @code{void func(void); if (func)}, and comparisons against the memory |
| address of a string literal, such as @code{if (x == "abc")}. Such |
| uses typically indicate a programmer error: the address of a function |
| always evaluates to true, so their use in a conditional usually |
| indicate that the programmer forgot the parentheses in a function |
| call; and comparisons against string literals result in unspecified |
| behavior and are not portable in C, so they usually indicate that the |
| programmer intended to use @code{strcmp}. This warning is enabled by |
| @option{-Wall}. |
| |
| @item -Wlogical-op |
| @opindex Wlogical-op |
| @opindex Wno-logical-op |
| Warn about suspicious uses of logical operators in expressions. |
| This includes using logical operators in contexts where a |
| bit-wise operator is likely to be expected. |
| |
| @item -Waggregate-return |
| @opindex Waggregate-return |
| @opindex Wno-aggregate-return |
| Warn if any functions that return structures or unions are defined or |
| called. (In languages where you can return an array, this also elicits |
| a warning.) |
| |
| @item -Wno-attributes |
| @opindex Wno-attributes |
| @opindex Wattributes |
| Do not warn if an unexpected @code{__attribute__} is used, such as |
| unrecognized attributes, function attributes applied to variables, |
| etc. This does not stop errors for incorrect use of supported |
| attributes. |
| |
| @item -Wno-builtin-macro-redefined |
| @opindex Wno-builtin-macro-redefined |
| @opindex Wbuiltin-macro-redefined |
| Do not warn if certain built-in macros are redefined. This suppresses |
| warnings for redefinition of @code{__TIMESTAMP__}, @code{__TIME__}, |
| @code{__DATE__}, @code{__FILE__}, and @code{__BASE_FILE__}. |
| |
| @item -Wstrict-prototypes @r{(C and Objective-C only)} |
| @opindex Wstrict-prototypes |
| @opindex Wno-strict-prototypes |
| Warn if a function is declared or defined without specifying the |
| argument types. (An old-style function definition is permitted without |
| a warning if preceded by a declaration that specifies the argument |
| types.) |
| |
| @item -Wold-style-declaration @r{(C and Objective-C only)} |
| @opindex Wold-style-declaration |
| @opindex Wno-old-style-declaration |
| Warn for obsolescent usages, according to the C Standard, in a |
| declaration. For example, warn if storage-class specifiers like |
| @code{static} are not the first things in a declaration. This warning |
| is also enabled by @option{-Wextra}. |
| |
| @item -Wold-style-definition @r{(C and Objective-C only)} |
| @opindex Wold-style-definition |
| @opindex Wno-old-style-definition |
| Warn if an old-style function definition is used. A warning is given |
| even if there is a previous prototype. |
| |
| @item -Wmissing-parameter-type @r{(C and Objective-C only)} |
| @opindex Wmissing-parameter-type |
| @opindex Wno-missing-parameter-type |
| A function parameter is declared without a type specifier in K&R-style |
| functions: |
| |
| @smallexample |
| void foo(bar) @{ @} |
| @end smallexample |
| |
| This warning is also enabled by @option{-Wextra}. |
| |
| @item -Wmissing-prototypes @r{(C and Objective-C only)} |
| @opindex Wmissing-prototypes |
| @opindex Wno-missing-prototypes |
| Warn if a global function is defined without a previous prototype |
| declaration. This warning is issued even if the definition itself |
| provides a prototype. Use this option to detect global functions |
| that do not have a matching prototype declaration in a header file. |
| This option is not valid for C++ because all function declarations |
| provide prototypes and a non-matching declaration will declare an |
| overload rather than conflict with an earlier declaration. |
| Use @option{-Wmissing-declarations} to detect missing declarations in C++. |
| |
| @item -Wmissing-declarations |
| @opindex Wmissing-declarations |
| @opindex Wno-missing-declarations |
| Warn if a global function is defined without a previous declaration. |
| Do so even if the definition itself provides a prototype. |
| Use this option to detect global functions that are not declared in |
| header files. In C, no warnings are issued for functions with previous |
| non-prototype declarations; use @option{-Wmissing-prototype} to detect |
| missing prototypes. In C++, no warnings are issued for function templates, |
| or for inline functions, or for functions in anonymous namespaces. |
| |
| @item -Wmissing-field-initializers |
| @opindex Wmissing-field-initializers |
| @opindex Wno-missing-field-initializers |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| Warn if a structure's initializer has some fields missing. For |
| example, the following code causes such a warning, because |
| @code{x.h} is implicitly zero: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| struct s x = @{ 3, 4 @}; |
| @end smallexample |
| |
| This option does not warn about designated initializers, so the following |
| modification does not trigger a warning: |
| |
| @smallexample |
| struct s @{ int f, g, h; @}; |
| struct s x = @{ .f = 3, .g = 4 @}; |
| @end smallexample |
| |
| This warning is included in @option{-Wextra}. To get other @option{-Wextra} |
| warnings without this one, use @option{-Wextra -Wno-missing-field-initializers}. |
| |
| @item -Wno-multichar |
| @opindex Wno-multichar |
| @opindex Wmultichar |
| Do not warn if a multicharacter constant (@samp{'FOOF'}) is used. |
| Usually they indicate a typo in the user's code, as they have |
| implementation-defined values, and should not be used in portable code. |
| |
| @item -Wnormalized=<none|id|nfc|nfkc> |
| @opindex Wnormalized= |
| @cindex NFC |
| @cindex NFKC |
| @cindex character set, input normalization |
| In ISO C and ISO C++, two identifiers are different if they are |
| different sequences of characters. However, sometimes when characters |
| outside the basic ASCII character set are used, you can have two |
| different character sequences that look the same. To avoid confusion, |
| the ISO 10646 standard sets out some @dfn{normalization rules} which |
| when applied ensure that two sequences that look the same are turned into |
| the same sequence. GCC can warn you if you are using identifiers that |
| have not been normalized; this option controls that warning. |
| |
| There are four levels of warning supported by GCC@. The default is |
| @option{-Wnormalized=nfc}, which warns about any identifier that is |
| not in the ISO 10646 ``C'' normalized form, @dfn{NFC}. NFC is the |
| recommended form for most uses. |
| |
| Unfortunately, there are some characters allowed in identifiers by |
| ISO C and ISO C++ that, when turned into NFC, are not allowed in |
| identifiers. That is, there's no way to use these symbols in portable |
| ISO C or C++ and have all your identifiers in NFC@. |
| @option{-Wnormalized=id} suppresses the warning for these characters. |
| It is hoped that future versions of the standards involved will correct |
| this, which is why this option is not the default. |
| |
| You can switch the warning off for all characters by writing |
| @option{-Wnormalized=none}. You should only do this if you |
| are using some other normalization scheme (like ``D''), because |
| otherwise you can easily create bugs that are literally impossible to see. |
| |
| Some characters in ISO 10646 have distinct meanings but look identical |
| in some fonts or display methodologies, especially once formatting has |
| been applied. For instance @code{\u207F}, ``SUPERSCRIPT LATIN SMALL |
| LETTER N'', displays just like a regular @code{n} that has been |
| placed in a superscript. ISO 10646 defines the @dfn{NFKC} |
| normalization scheme to convert all these into a standard form as |
| well, and GCC warns if your code is not in NFKC if you use |
| @option{-Wnormalized=nfkc}. This warning is comparable to warning |
| about every identifier that contains the letter O because it might be |
| confused with the digit 0, and so is not the default, but may be |
| useful as a local coding convention if the programming environment |
| cannot be fixed to display these characters distinctly. |
| |
| @item -Wno-deprecated |
| @opindex Wno-deprecated |
| @opindex Wdeprecated |
| Do not warn about usage of deprecated features. @xref{Deprecated Features}. |
| |
| @item -Wno-deprecated-declarations |
| @opindex Wno-deprecated-declarations |
| @opindex Wdeprecated-declarations |
| Do not warn about uses of functions (@pxref{Function Attributes}), |
| variables (@pxref{Variable Attributes}), and types (@pxref{Type |
| Attributes}) marked as deprecated by using the @code{deprecated} |
| attribute. |
| |
| @item -Wno-overflow |
| @opindex Wno-overflow |
| @opindex Woverflow |
| Do not warn about compile-time overflow in constant expressions. |
| |
| @item -Woverride-init @r{(C and Objective-C only)} |
| @opindex Woverride-init |
| @opindex Wno-override-init |
| @opindex W |
| @opindex Wextra |
| @opindex Wno-extra |
| Warn if an initialized field without side effects is overridden when |
| using designated initializers (@pxref{Designated Inits, , Designated |
| Initializers}). |
| |
| This warning is included in @option{-Wextra}. To get other |
| @option{-Wextra} warnings without this one, use @option{-Wextra |
| -Wno-override-init}. |
| |
| @item -Wpacked |
| @opindex Wpacked |
| @opindex Wno-packed |
| Warn if a structure is given the packed attribute, but the packed |
| attribute has no effect on the layout or size of the structure. |
| Such structures may be mis-aligned for little benefit. For |
| instance, in this code, the variable @code{f.x} in @code{struct bar} |
| is misaligned even though @code{struct bar} does not itself |
| have the packed attribute: |
| |
| @smallexample |
| @group |
| struct foo @{ |
| int x; |
| char a, b, c, d; |
| @} __attribute__((packed)); |
| struct bar @{ |
| char z; |
| struct foo f; |
| @}; |
| @end group |
| @end smallexample |
| |
| @item -Wpacked-bitfield-compat |
| @opindex Wpacked-bitfield-compat |
| @opindex Wno-packed-bitfield-compat |
| The 4.1, 4.2 and 4.3 series of GCC ignore the @code{packed} attribute |
| on bit-fields of type @code{char}. This has been fixed in GCC 4.4 but |
| the change can lead to differences in the structure layout. GCC |
| informs you when the offset of such a field has changed in GCC 4.4. |
| For example there is no longer a 4-bit padding between field @code{a} |
| and @code{b} in this structure: |
| |
| @smallexample |
| struct foo |
| @{ |
| char a:4; |
| char b:8; |
| @} __attribute__ ((packed)); |
| @end smallexample |
| |
| This warning is enabled by default. Use |
| @option{-Wno-packed-bitfield-compat} to disable this warning. |
| |
| @item -Wpadded |
| @opindex Wpadded |
| @opindex Wno-padded |
| Warn if padding is included in a structure, either to align an element |
| of the structure or to align the whole structure. Sometimes when this |
| happens it is possible to rearrange the fields of the structure to |
| reduce the padding and so make the structure smaller. |
| |
| @item -Wredundant-decls |
| @opindex Wredundant-decls |
| @opindex Wno-redundant-decls |
| Warn if anything is declared more than once in the same scope, even in |
| cases where multiple declaration is valid and changes nothing. |
| |
| @item -Wnested-externs @r{(C and Objective-C only)} |
| @opindex Wnested-externs |
| @opindex Wno-nested-externs |
| Warn if an @code{extern} declaration is encountered within a function. |
| |
| @item -Winline |
| @opindex Winline |
| @opindex Wno-inline |
| Warn if a function that is declared as inline cannot be inlined. |
| Even with this option, the compiler does not warn about failures to |
| inline functions declared in system headers. |
| |
| The compiler uses a variety of heuristics to determine whether or not |
| to inline a function. For example, the compiler takes into account |
| the size of the function being inlined and the amount of inlining |
| that has already been done in the current function. Therefore, |
| seemingly insignificant changes in the source program can cause the |
| warnings produced by @option{-Winline} to appear or disappear. |
| |
| @item -Wno-invalid-offsetof @r{(C++ and Objective-C++ only)} |
| @opindex Wno-invalid-offsetof |
| @opindex Winvalid-offsetof |
| Suppress warnings from applying the @samp{offsetof} macro to a non-POD |
| type. According to the 1998 ISO C++ standard, applying @samp{offsetof} |
| to a non-POD type is undefined. In existing C++ implementations, |
| however, @samp{offsetof} typically gives meaningful results even when |
| applied to certain kinds of non-POD types (such as a simple |
| @samp{struct} that fails to be a POD type only by virtue of having a |
| constructor). This flag is for users who are aware that they are |
| writing nonportable code and who have deliberately chosen to ignore the |
| warning about it. |
| |
| The restrictions on @samp{offsetof} may be relaxed in a future version |
| of the C++ standard. |
| |
| @item -Wno-int-to-pointer-cast |
| @opindex Wno-int-to-pointer-cast |
| @opindex Wint-to-pointer-cast |
| Suppress warnings from casts to pointer type of an integer of a |
| different size. In C++, casting to a pointer type of smaller size is |
| an error. @option{Wint-to-pointer-cast} is enabled by default. |
| |
| |
| @item -Wno-pointer-to-int-cast @r{(C and Objective-C only)} |
| @opindex Wno-pointer-to-int-cast |
| @opindex Wpointer-to-int-cast |
| Suppress warnings from casts from a pointer to an integer type of a |
| different size. |
| |
| @item -Winvalid-pch |
| @opindex Winvalid-pch |
| @opindex Wno-invalid-pch |
| Warn if a precompiled header (@pxref{Precompiled Headers}) is found in |
| the search path but can't be used. |
| |
| @item -Wlong-long |
| @opindex Wlong-long |
| @opindex Wno-long-long |
| Warn if @samp{long long} type is used. This is enabled by either |
| @option{-Wpedantic} or @option{-Wtraditional} in ISO C90 and C++98 |
| modes. To inhibit the warning messages, use @option{-Wno-long-long}. |
| |
| @item -Wvariadic-macros |
| @opindex Wvariadic-macros |
| @opindex Wno-variadic-macros |
| Warn if variadic macros are used in pedantic ISO C90 mode, or the GNU |
| alternate syntax when in pedantic ISO C99 mode. This is default. |
| To inhibit the warning messages, use @option{-Wno-variadic-macros}. |
| |
| @item -Wvarargs |
| @opindex Wvarargs |
| @opindex Wno-varargs |
| Warn upon questionable usage of the macros used to handle variable |
| arguments like @samp{va_start}. This is default. To inhibit the |
| warning messages, use @option{-Wno-varargs}. |
| |
| @item -Wvector-operation-performance |
| @opindex Wvector-operation-performance |
| @opindex Wno-vector-operation-performance |
| Warn if vector operation is not implemented via SIMD capabilities of the |
| architecture. Mainly useful for the performance tuning. |
| Vector operation can be implemented @code{piecewise}, which means that the |
| scalar operation is performed on every vector element; |
| @code{in parallel}, which means that the vector operation is implemented |
| using scalars of wider type, which normally is more performance efficient; |
| and @code{as a single scalar}, which means that vector fits into a |
| scalar type. |
| |
| @item -Wvla |
| @opindex Wvla |
| @opindex Wno-vla |
| Warn if variable length array is used in the code. |
| @option{-Wno-vla} prevents the @option{-Wpedantic} warning of |
| the variable length array. |
| |
| @item -Wvolatile-register-var |
| @opindex Wvolatile-register-var |
| @opindex Wno-volatile-register-var |
| Warn if a register variable is declared volatile. The volatile |
| modifier does not inhibit all optimizations that may eliminate reads |
| and/or writes to register variables. This warning is enabled by |
| @option{-Wall}. |
| |
| @item -Wdisabled-optimization |
| @opindex Wdisabled-optimization |
| @opindex Wno-disabled-optimization |
| Warn if a requested optimization pass is disabled. This warning does |
| not generally indicate that there is anything wrong with your code; it |
| merely indicates that GCC's optimizers are unable to handle the code |
| effectively. Often, the problem is that your code is too big or too |
| complex; GCC refuses to optimize programs when the optimization |
| itself is likely to take inordinate amounts of time. |
| |
| @item -Wpointer-sign @r{(C and Objective-C only)} |
| @opindex Wpointer-sign |
| @opindex Wno-pointer-sign |
| Warn for pointer argument passing or assignment with different signedness. |
| This option is only supported for C and Objective-C@. It is implied by |
| @option{-Wall} and by @option{-Wpedantic}, which can be disabled with |
| @option{-Wno-pointer-sign}. |
| |
| @item -Wstack-protector |
| @opindex Wstack-protector |
| @opindex Wno-stack-protector |
| This option is only active when @option{-fstack-protector} is active. It |
| warns about functions that are not protected against stack smashing. |
| |
| @item -Wno-mudflap |
| @opindex Wno-mudflap |
| Suppress warnings about constructs that cannot be instrumented by |
| @option{-fmudflap}. |
| |
| @item -Woverlength-strings |
| @opindex Woverlength-strings |
| @opindex Wno-overlength-strings |
| Warn about string constants that are longer than the ``minimum |
| maximum'' length specified in the C standard. Modern compilers |
| generally allow string constants that are much longer than the |
| standard's minimum limit, but very portable programs should avoid |
| using longer strings. |
| |
| The limit applies @emph{after} string constant concatenation, and does |
| not count the trailing NUL@. In C90, the limit was 509 characters; in |
| C99, it was raised to 4095. C++98 does not specify a normative |
| minimum maximum, so we do not diagnose overlength strings in C++@. |
| |
| This option is implied by @option{-Wpedantic}, and can be disabled with |
| @option{-Wno-overlength-strings}. |
| |
| @item -Wunsuffixed-float-constants @r{(C and Objective-C only)} |
| @opindex Wunsuffixed-float-constants |
| |
| Issue a warning for any floating constant that does not have |
| a suffix. When used together with @option{-Wsystem-headers} it |
| warns about such constants in system header files. This can be useful |
| when preparing code to use with the @code{FLOAT_CONST_DECIMAL64} pragma |
| from the decimal floating-point extension to C99. |
| @end table |
| |
| @node Debugging Options |
| @section Options for Debugging Your Program or GCC |
| @cindex options, debugging |
| @cindex debugging information options |
| |
| GCC has various special options that are used for debugging |
| either your program or GCC: |
| |
| @table @gcctabopt |
| @item -g |
| @opindex g |
| Produce debugging information in the operating system's native format |
| (stabs, COFF, XCOFF, or DWARF 2)@. GDB can work with this debugging |
| information. |
| |
| On most systems that use stabs format, @option{-g} enables use of extra |
| debugging information that only GDB can use; this extra information |
| makes debugging work better in GDB but probably makes other debuggers |
| crash or |
| refuse to read the program. If you want to control for certain whether |
| to generate the extra information, use @option{-gstabs+}, @option{-gstabs}, |
| @option{-gxcoff+}, @option{-gxcoff}, or @option{-gvms} (see below). |
| |
| GCC allows you to use @option{-g} with |
| @option{-O}. The shortcuts taken by optimized code may occasionally |
| produce surprising results: some variables you declared may not exist |
| at all; flow of control may briefly move where you did not expect it; |
| some statements may not be executed because they compute constant |
| results or their values are already at hand; some statements may |
| execute in different places because they have been moved out of loops. |
| |
| Nevertheless it proves possible to debug optimized output. This makes |
| it reasonable to use the optimizer for programs that might have bugs. |
| |
| The following options are useful when GCC is generated with the |
| capability for more than one debugging format. |
| |
| @item -ggdb |
| @opindex ggdb |
| Produce debugging information for use by GDB@. This means to use the |
| most expressive format available (DWARF 2, stabs, or the native format |
| if neither of those are supported), including GDB extensions if at all |
| possible. |
| |
| @item -gpubnames |
| @opindex gpubnames |
| Generate dwarf .debug_pubnames and .debug_pubtypes sections. |
| |
| @item -gstabs |
| @opindex gstabs |
| Produce debugging information in stabs format (if that is supported), |
| without GDB extensions. This is the format used by DBX on most BSD |
| systems. On MIPS, Alpha and System V Release 4 systems this option |
| produces stabs debugging output that is not understood by DBX or SDB@. |
| On System V Release 4 systems this option requires the GNU assembler. |
| |
| @item -feliminate-unused-debug-symbols |
| @opindex feliminate-unused-debug-symbols |
| Produce debugging information in stabs format (if that is supported), |
| for only symbols that are actually used. |
| |
| @item -femit-class-debug-always |
| Instead of emitting debugging information for a C++ class in only one |
| object file, emit it in all object files using the class. This option |
| should be used only with debuggers that are unable to handle the way GCC |
| normally emits debugging information for classes because using this |
| option increases the size of debugging information by as much as a |
| factor of two. |
| |
| @item -fdebug-types-section |
| @opindex fdebug-types-section |
| @opindex fno-debug-types-section |
| When using DWARF Version 4 or higher, type DIEs can be put into |
| their own @code{.debug_types} section instead of making them part of the |
| @code{.debug_info} section. It is more efficient to put them in a separate |
| comdat sections since the linker can then remove duplicates. |
| But not all DWARF consumers support @code{.debug_types} sections yet |
| and on some objects @code{.debug_types} produces larger instead of smaller |
| debugging information. |
| |
| @item -gstabs+ |
| @opindex gstabs+ |
| Produce debugging information in stabs format (if that is supported), |
| using GNU extensions understood only by the GNU debugger (GDB)@. The |
| use of these extensions is likely to make other debuggers crash or |
| refuse to read the program. |
| |
| @item -gcoff |
| @opindex gcoff |
| Produce debugging information in COFF format (if that is supported). |
| This is the format used by SDB on most System V systems prior to |
| System V Release 4. |
| |
| @item -gxcoff |
| @opindex gxcoff |
| Produce debugging information in XCOFF format (if that is supported). |
| This is the format used by the DBX debugger on IBM RS/6000 systems. |
| |
| @item -gxcoff+ |
| @opindex gxcoff+ |
| Produce debugging information in XCOFF format (if that is supported), |
| using GNU extensions understood only by the GNU debugger (GDB)@. The |
| use of these extensions is likely to make other debuggers crash or |
| refuse to read the program, and may cause assemblers other than the GNU |
| assembler (GAS) to fail with an error. |
| |
| @item -gdwarf-@var{version} |
| @opindex gdwarf-@var{version} |
| Produce debugging information in DWARF format (if that is supported). |
| The value of @var{version} may be either 2, 3 or 4; the default version |
| for most targets is 4. |
| |
| Note that with DWARF Version 2, some ports require and always |
| use some non-conflicting DWARF 3 extensions in the unwind tables. |
| |
| Version 4 may require GDB 7.0 and @option{-fvar-tracking-assignments} |
| for maximum benefit. |
| |
| @item -grecord-gcc-switches |
| @opindex grecord-gcc-switches |
| This switch causes the command-line options used to invoke the |
| compiler that may affect code generation to be appended to the |
| DW_AT_producer attribute in DWARF debugging information. The options |
| are concatenated with spaces separating them from each other and from |
| the compiler version. See also @option{-frecord-gcc-switches} for another |
| way of storing compiler options into the object file. This is the default. |
| |
| @item -gno-record-gcc-switches |
| @opindex gno-record-gcc-switches |
| Disallow appending command-line options to the DW_AT_producer attribute |
| in DWARF debugging information. |
| |
| @item -gstrict-dwarf |
| @opindex gstrict-dwarf |
| Disallow using extensions of later DWARF standard version than selected |
| with @option{-gdwarf-@var{version}}. On most targets using non-conflicting |
| DWARF extensions from later standard versions is allowed. |
| |
| @item -gno-strict-dwarf |
| @opindex gno-strict-dwarf |
| Allow using extensions of later DWARF standard version than selected with |
| @option{-gdwarf-@var{version}}. |
| |
| @item -gvms |
| @opindex gvms |
| Produce debugging information in Alpha/VMS debug format (if that is |
| supported). This is the format used by DEBUG on Alpha/VMS systems. |
| |
| @item -g@var{level} |
| @itemx -ggdb@var{level} |
| @itemx -gstabs@var{level} |
| @itemx -gcoff@var{level} |
| @itemx -gxcoff@var{level} |
| @itemx -gvms@var{level} |
| Request debugging information and also use @var{level} to specify how |
| much information. The default level is 2. |
| |
| Level 0 produces no debug information at all. Thus, @option{-g0} negates |
| @option{-g}. |
| |
| Level 1 produces minimal information, enough for making backtraces in |
| parts of the program that you don't plan to debug. This includes |
| descriptions of functions and external variables, but no information |
| about local variables and no line numbers. |
| |
| Level 3 includes extra information, such as all the macro definitions |
| present in the program. Some debuggers support macro expansion when |
| you use @option{-g3}. |
| |
| @option{-gdwarf-2} does not accept a concatenated debug level, because |
| GCC used to support an option @option{-gdwarf} that meant to generate |
| debug information in version 1 of the DWARF format (which is very |
| different from version 2), and it would have been too confusing. That |
| debug format is long obsolete, but the option cannot be changed now. |
| Instead use an additional @option{-g@var{level}} option to change the |
| debug level for DWARF. |
| |
| @item -gtoggle |
| @opindex gtoggle |
| Turn off generation of debug info, if leaving out this option |
| generates it, or turn it on at level 2 otherwise. The position of this |
| argument in the command line does not matter; it takes effect after all |
| other options are processed, and it does so only once, no matter how |
| many times it is given. This is mainly intended to be used with |
| @option{-fcompare-debug}. |
| |
| @item -fdump-final-insns@r{[}=@var{file}@r{]} |
| @opindex fdump-final-insns |
| Dump the final internal representation (RTL) to @var{file}. If the |
| optional argument is omitted (or if @var{file} is @code{.}), the name |
| of the dump file is determined by appending @code{.gkd} to the |
| compilation output file name. |
| |
| @item -fcompare-debug@r{[}=@var{opts}@r{]} |
| @opindex fcompare-debug |
| @opindex fno-compare-debug |
| If no error occurs during compilation, run the compiler a second time, |
| adding @var{opts} and @option{-fcompare-debug-second} to the arguments |
| passed to the second compilation. Dump the final internal |
| representation in both compilations, and print an error if they differ. |
| |
| If the equal sign is omitted, the default @option{-gtoggle} is used. |
| |
| The environment variable @env{GCC_COMPARE_DEBUG}, if defined, non-empty |
| and nonzero, implicitly enables @option{-fcompare-debug}. If |
| @env{GCC_COMPARE_DEBUG} is defined to a string starting with a dash, |
| then it is used for @var{opts}, otherwise the default @option{-gtoggle} |
| is used. |
| |
| @option{-fcompare-debug=}, with the equal sign but without @var{opts}, |
| is equivalent to @option{-fno-compare-debug}, which disables the dumping |
| of the final representation and the second compilation, preventing even |
| @env{GCC_COMPARE_DEBUG} from taking effect. |
| |
| To verify full coverage during @option{-fcompare-debug} testing, set |
| @env{GCC_COMPARE_DEBUG} to say @samp{-fcompare-debug-not-overridden}, |
| which GCC rejects as an invalid option in any actual compilation |
| (rather than preprocessing, assembly or linking). To get just a |
| warning, setting @env{GCC_COMPARE_DEBUG} to @samp{-w%n-fcompare-debug |
| not overridden} will do. |
| |
| @item -fcompare-debug-second |
| @opindex fcompare-debug-second |
| This option is implicitly passed to the compiler for the second |
| compilation requested by @option{-fcompare-debug}, along with options to |
| silence warnings, and omitting other options that would cause |
| side-effect compiler outputs to files or to the standard output. Dump |
| files and preserved temporary files are renamed so as to contain the |
| @code{.gk} additional extension during the second compilation, to avoid |
| overwriting those generated by the first. |
| |
| When this option is passed to the compiler driver, it causes the |
| @emph{first} compilation to be skipped, which makes it useful for little |
| other than debugging the compiler proper. |
| |
| @item -feliminate-dwarf2-dups |
| @opindex feliminate-dwarf2-dups |
| Compress DWARF 2 debugging information by eliminating duplicated |
| information about each symbol. This option only makes sense when |
| generating DWARF 2 debugging information with @option{-gdwarf-2}. |
| |
| @item -femit-struct-debug-baseonly |
| Emit debug information for struct-like types |
| only when the base name of the compilation source file |
| matches the base name of file in which the struct is defined. |
| |
| This option substantially reduces the size of debugging information, |
| but at significant potential loss in type information to the debugger. |
| See @option{-femit-struct-debug-reduced} for a less aggressive option. |
| See @option{-femit-struct-debug-detailed} for more detailed control. |
| |
| This option works only with DWARF 2. |
| |
| @item -femit-struct-debug-reduced |
| Emit debug information for struct-like types |
| only when the base name of the compilation source file |
| matches the base name of file in which the type is defined, |
| unless the struct is a template or defined in a system header. |
| |
| This option significantly reduces the size of debugging information, |
| with some potential loss in type information to the debugger. |
| See @option{-femit-struct-debug-baseonly} for a more aggressive option. |
| See @option{-femit-struct-debug-detailed} for more detailed control. |
| |
| This option works only with DWARF 2. |
| |
| @item -femit-struct-debug-detailed@r{[}=@var{spec-list}@r{]} |
| Specify the struct-like types |
| for which the compiler generates debug information. |
| The intent is to reduce duplicate struct debug information |
| between different object files within the same program. |
| |
| This option is a detailed version of |
| @option{-femit-struct-debug-reduced} and @option{-femit-struct-debug-baseonly}, |
| which serves for most needs. |
| |
| A specification has the syntax@* |
| [@samp{dir:}|@samp{ind:}][@samp{ord:}|@samp{gen:}](@samp{any}|@samp{sys}|@samp{base}|@samp{none}) |
| |
| The optional first word limits the specification to |
| structs that are used directly (@samp{dir:}) or used indirectly (@samp{ind:}). |
| A struct type is used directly when it is the type of a variable, member. |
| Indirect uses arise through pointers to structs. |
| That is, when use of an incomplete struct is valid, the use is indirect. |
| An example is |
| @samp{struct one direct; struct two * indirect;}. |
| |
| The optional second word limits the specification to |
| ordinary structs (@samp{ord:}) or generic structs (@samp{gen:}). |
| Generic structs are a bit complicated to explain. |
| For C++, these are non-explicit specializations of template classes, |
| or non-template classes within the above. |
| Other programming languages have generics, |
| but @option{-femit-struct-debug-detailed} does not yet implement them. |
| |
| The third word specifies the source files for those |
| structs for which the compiler should emit debug information. |
| The values @samp{none} and @samp{any} have the normal meaning. |
| The value @samp{base} means that |
| the base of name of the file in which the type declaration appears |
| must match the base of the name of the main compilation file. |
| In practice, this means that when compiling @file{foo.c}, debug information |
| is generated for types declared in that file and @file{foo.h}, |
| but not other header files. |
| The value @samp{sys} means those types satisfying @samp{base} |
| or declared in system or compiler headers. |
| |
| You may need to experiment to determine the best settings for your application. |
| |
| The default is @option{-femit-struct-debug-detailed=all}. |
| |
| This option works only with DWARF 2. |
| |
| @item -fno-merge-debug-strings |
| @opindex fmerge-debug-strings |
| @opindex fno-merge-debug-strings |
| Direct the linker to not merge together strings in the debugging |
| information that are identical in different object files. Merging is |
| not supported by all assemblers or linkers. Merging decreases the size |
| of the debug information in the output file at the cost of increasing |
| link processing time. Merging is enabled by default. |
| |
| @item -fdebug-prefix-map=@var{old}=@var{new} |
| @opindex fdebug-prefix-map |
| When compiling files in directory @file{@var{old}}, record debugging |
| information describing them as in @file{@var{new}} instead. |
| |
| @item -fno-dwarf2-cfi-asm |
| @opindex fdwarf2-cfi-asm |
| @opindex fno-dwarf2-cfi-asm |
| Emit DWARF 2 unwind info as compiler generated @code{.eh_frame} section |
| instead of using GAS @code{.cfi_*} directives. |
| |
| @cindex @command{prof} |
| @item -p |
| @opindex p |
| Generate extra code to write profile information suitable for the |
| analysis program @command{prof}. You must use this option when compiling |
| the source files you want data about, and you must also use it when |
| linking. |
| |
| @cindex @command{gprof} |
| @item -pg |
| @opindex pg |
| Generate extra code to write profile information suitable for the |
| analysis program @command{gprof}. You must use this option when compiling |
| the source files you want data about, and you must also use it when |
| linking. |
| |
| @item -Q |
| @opindex Q |
| Makes the compiler print out each function name as it is compiled, and |
| print some statistics about each pass when it finishes. |
| |
| @item -ftime-report |
| @opindex ftime-report |
| Makes the compiler print some statistics about the time consumed by each |
| pass when it finishes. |
| |
| @item -fmem-report |
| @opindex fmem-report |
| Makes the compiler print some statistics about permanent memory |
| allocation when it finishes. |
| |
| @item -fmem-report-wpa |
| @opindex fmem-report-wpa |
| Makes the compiler print some statistics about permanent memory |
| allocation for the WPA phase only. |
| |
| @item -fpre-ipa-mem-report |
| @opindex fpre-ipa-mem-report |
| @item -fpost-ipa-mem-report |
| @opindex fpost-ipa-mem-report |
| Makes the compiler print some statistics about permanent memory |
| allocation before or after interprocedural optimization. |
| |
| @item -fstack-usage |
| @opindex fstack-usage |
| Makes the compiler output stack usage information for the program, on a |
| per-function basis. The filename for the dump is made by appending |
| @file{.su} to the @var{auxname}. @var{auxname} is generated from the name of |
| the output file, if explicitly specified and it is not an executable, |
| otherwise it is the basename of the source file. An entry is made up |
| of three fields: |
| |
| @itemize |
| @item |
| The name of the function. |
| @item |
| A number of bytes. |
| @item |
| One or more qualifiers: @code{static}, @code{dynamic}, @code{bounded}. |
| @end itemize |
| |
| The qualifier @code{static} means that the function manipulates the stack |
| statically: a fixed number of bytes are allocated for the frame on function |
| entry and released on function exit; no stack adjustments are otherwise made |
| in the function. The second field is this fixed number of bytes. |
| |
| The qualifier @code{dynamic} means that the function manipulates the stack |
| dynamically: in addition to the static allocation described above, stack |
| adjustments are made in the body of the function, for example to push/pop |
| arguments around function calls. If the qualifier @code{bounded} is also |
| present, the amount of these adjustments is bounded at compile time and |
| the second field is an upper bound of the total amount of stack used by |
| the function. If it is not present, the amount of these adjustments is |
| not bounded at compile time and the second field only represents the |
| bounded part. |
| |
| @item -fprofile-arcs |
| @opindex fprofile-arcs |
| Add code so that program flow @dfn{arcs} are instrumented. During |
| execution the program records how many times each branch and call is |
| executed and how many times it is taken or returns. When the compiled |
| program exits it saves this data to a file called |
| @file{@var{auxname}.gcda} for each source file. The data may be used for |
| profile-directed optimizations (@option{-fbranch-probabilities}), or for |
| test coverage analysis (@option{-ftest-coverage}). Each object file's |
| @var{auxname} is generated from the name of the output file, if |
| explicitly specified and it is not the final executable, otherwise it is |
| the basename of the source file. In both cases any suffix is removed |
| (e.g.@: @file{foo.gcda} for input file @file{dir/foo.c}, or |
| @file{dir/foo.gcda} for output file specified as @option{-o dir/foo.o}). |
| @xref{Cross-profiling}. |
| |
| @cindex @command{gcov} |
| @item --coverage |
| @opindex coverage |
| |
| This option is used to compile and link code instrumented for coverage |
| analysis. The option is a synonym for @option{-fprofile-arcs} |
| @option{-ftest-coverage} (when compiling) and @option{-lgcov} (when |
| linking). See the documentation for those options for more details. |
| |
| @itemize |
| |
| @item |
| Compile the source files with @option{-fprofile-arcs} plus optimization |
| and code generation options. For test coverage analysis, use the |
| additional @option{-ftest-coverage} option. You do not need to profile |
| every source file in a program. |
| |
| @item |
| Link your object files with @option{-lgcov} or @option{-fprofile-arcs} |
| (the latter implies the former). |
| |
| @item |
| Run the program on a representative workload to generate the arc profile |
| information. This may be repeated any number of times. You can run |
| concurrent instances of your program, and provided that the file system |
| supports locking, the data files will be correctly updated. Also |
| @code{fork} calls are detected and correctly handled (double counting |
| will not happen). |
| |
| @item |
| For profile-directed optimizations, compile the source files again with |
| the same optimization and code generation options plus |
| @option{-fbranch-probabilities} (@pxref{Optimize Options,,Options that |
| Control Optimization}). |
| |
| @item |
| For test coverage analysis, use @command{gcov} to produce human readable |
| information from the @file{.gcno} and @file{.gcda} files. Refer to the |
| @command{gcov} documentation for further information. |
| |
| @end itemize |
| |
| With @option{-fprofile-arcs}, for each function of your program GCC |
| creates a program flow graph, then finds a spanning tree for the graph. |
| Only arcs that are not on the spanning tree have to be instrumented: the |
| compiler adds code to count the number of times that these arcs are |
| executed. When an arc is the only exit or only entrance to a block, the |
| instrumentation code can be added to the block; otherwise, a new basic |
| block must be created to hold the instrumentation code. |
| |
| @need 2000 |
| @item -ftest-coverage |
| @opindex ftest-coverage |
| Produce a notes file that the @command{gcov} code-coverage utility |
| (@pxref{Gcov,, @command{gcov}---a Test Coverage Program}) can use to |
| show program coverage. Each source file's note file is called |
| @file{@var{auxname}.gcno}. Refer to the @option{-fprofile-arcs} option |
| above for a description of @var{auxname} and instructions on how to |
| generate test coverage data. Coverage data matches the source files |
| more closely if you do not optimize. |
| |
| @item -fdbg-cnt-list |
| @opindex fdbg-cnt-list |
| Print the name and the counter upper bound for all debug counters. |
| |
| |
| @item -fdbg-cnt=@var{counter-value-list} |
| @opindex fdbg-cnt |
| Set the internal debug counter upper bound. @var{counter-value-list} |
| is a comma-separated list of @var{name}:@var{value} pairs |
| which sets the upper bound of each debug counter @var{name} to @var{value}. |
| All debug counters have the initial upper bound of @code{UINT_MAX}; |
| thus @code{dbg_cnt()} returns true always unless the upper bound |
| is set by this option. |
| For example, with @option{-fdbg-cnt=dce:10,tail_call:0}, |
| @code{dbg_cnt(dce)} returns true only for first 10 invocations. |
| |
| @itemx -fenable-@var{kind}-@var{pass} |
| @itemx -fdisable-@var{kind}-@var{pass}=@var{range-list} |
| @opindex fdisable- |
| @opindex fenable- |
| |
| This is a set of options that are used to explicitly disable/enable |
| optimization passes. These options are intended for use for debugging GCC. |
| Compiler users should use regular options for enabling/disabling |
| passes instead. |
| |
| @table @gcctabopt |
| |
| @item -fdisable-ipa-@var{pass} |
| Disable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. |
| |
| @item -fdisable-rtl-@var{pass} |
| @itemx -fdisable-rtl-@var{pass}=@var{range-list} |
| Disable RTL pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. @var{range-list} is a |
| comma-separated list of function ranges or assembler names. Each range is a number |
| pair separated by a colon. The range is inclusive in both ends. If the range |
| is trivial, the number pair can be simplified as a single number. If the |
| function's cgraph node's @var{uid} falls within one of the specified ranges, |
| the @var{pass} is disabled for that function. The @var{uid} is shown in the |
| function header of a dump file, and the pass names can be dumped by using |
| option @option{-fdump-passes}. |
| |
| @item -fdisable-tree-@var{pass} |
| @itemx -fdisable-tree-@var{pass}=@var{range-list} |
| Disable tree pass @var{pass}. See @option{-fdisable-rtl} for the description of |
| option arguments. |
| |
| @item -fenable-ipa-@var{pass} |
| Enable IPA pass @var{pass}. @var{pass} is the pass name. If the same pass is |
| statically invoked in the compiler multiple times, the pass name should be |
| appended with a sequential number starting from 1. |
| |
| @item -fenable-rtl-@var{pass} |
| @itemx -fenable-rtl-@var{pass}=@var{range-list} |
| Enable RTL pass @var{pass}. See @option{-fdisable-rtl} for option argument |
| description and examples. |
| |
| @item -fenable-tree-@var{pass} |
| @itemx -fenable-tree-@var{pass}=@var{range-list} |
| Enable tree pass @var{pass}. See @option{-fdisable-rtl} for the description |
| of option arguments. |
| |
| @end table |
| |
| Here are some examples showing uses of these options. |
| |
| @smallexample |
| |
| # disable ccp1 for all functions |
| -fdisable-tree-ccp1 |
| # disable complete unroll for function whose cgraph node uid is 1 |
| -fenable-tree-cunroll=1 |
| # disable gcse2 for functions at the following ranges [1,1], |
| # [300,400], and [400,1000] |
| # disable gcse2 for functions foo and foo2 |
| -fdisable-rtl-gcse2=foo,foo2 |
| # disable early inlining |
| -fdisable-tree-einline |
| # disable ipa inlining |
| -fdisable-ipa-inline |
| # enable tree full unroll |
| -fenable-tree-unroll |
| |
| @end smallexample |
| |
| @item -d@var{letters} |
| @itemx -fdump-rtl-@var{pass} |
| @opindex d |
| Says to make debugging dumps during compilation at times specified by |
| @var{letters}. This is used for debugging the RTL-based passes of the |
| compiler. The file names for most of the dumps are made by appending |
| a pass number and a word to the @var{dumpname}, and the files are |
| created in the directory of the output file. Note that the pass |
| number is computed statically as passes get registered into the pass |
| manager. Thus the numbering is not related to the dynamic order of |
| execution of passes. In particular, a pass installed by a plugin |
| could have a number over 200 even if it executed quite early. |
| @var{dumpname} is generated from the name of the output file, if |
| explicitly specified and it is not an executable, otherwise it is the |
| basename of the source file. These switches may have different effects |
| when @option{-E} is used for preprocessing. |
| |
| Debug dumps can be enabled with a @option{-fdump-rtl} switch or some |
| @option{-d} option @var{letters}. Here are the possible |
| letters for use in @var{pass} and @var{letters}, and their meanings: |
| |
| @table @gcctabopt |
| |
| @item -fdump-rtl-alignments |
| @opindex fdump-rtl-alignments |
| Dump after branch alignments have been computed. |
| |
| @item -fdump-rtl-asmcons |
| @opindex fdump-rtl-asmcons |
| Dump after fixing rtl statements that have unsatisfied in/out constraints. |
| |
| @item -fdump-rtl-auto_inc_dec |
| @opindex fdump-rtl-auto_inc_dec |
| Dump after auto-inc-dec discovery. This pass is only run on |
| architectures that have auto inc or auto dec instructions. |
| |
| @item -fdump-rtl-barriers |
| @opindex fdump-rtl-barriers |
| Dump after cleaning up the barrier instructions. |
| |
| @item -fdump-rtl-bbpart |
| @opindex fdump-rtl-bbpart |
| Dump after partitioning hot and cold basic blocks. |
| |
| @item -fdump-rtl-bbro |
| @opindex fdump-rtl-bbro |
| Dump after block reordering. |
| |
| @item -fdump-rtl-btl1 |
| @itemx -fdump-rtl-btl2 |
| @opindex fdump-rtl-btl2 |
| @opindex fdump-rtl-btl2 |
| @option{-fdump-rtl-btl1} and @option{-fdump-rtl-btl2} enable dumping |
| after the two branch |
| target load optimization passes. |
| |
| @item -fdump-rtl-bypass |
| @opindex fdump-rtl-bypass |
| Dump after jump bypassing and control flow optimizations. |
| |
| @item -fdump-rtl-combine |
| @opindex fdump-rtl-combine |
| Dump after the RTL instruction combination pass. |
| |
| @item -fdump-rtl-compgotos |
| @opindex fdump-rtl-compgotos |
| Dump after duplicating the computed gotos. |
| |
| @item -fdump-rtl-ce1 |
| @itemx -fdump-rtl-ce2 |
| @itemx -fdump-rtl-ce3 |
| @opindex fdump-rtl-ce1 |
| @opindex fdump-rtl-ce2 |
| @opindex fdump-rtl-ce3 |
| @option{-fdump-rtl-ce1}, @option{-fdump-rtl-ce2}, and |
| @option{-fdump-rtl-ce3} enable dumping after the three |
| if conversion passes. |
| |
| @itemx -fdump-rtl-cprop_hardreg |
| @opindex fdump-rtl-cprop_hardreg |
| Dump after hard register copy propagation. |
| |
| @itemx -fdump-rtl-csa |
| @opindex fdump-rtl-csa |
| Dump after combining stack adjustments. |
| |
| @item -fdump-rtl-cse1 |
| @itemx -fdump-rtl-cse2 |
| @opindex fdump-rtl-cse1 |
| @opindex fdump-rtl-cse2 |
| @option{-fdump-rtl-cse1} and @option{-fdump-rtl-cse2} enable dumping after |
| the two common subexpression elimination passes. |
| |
| @itemx -fdump-rtl-dce |
| @opindex fdump-rtl-dce |
| Dump after the standalone dead code elimination passes. |
| |
| @itemx -fdump-rtl-dbr |
| @opindex fdump-rtl-dbr |
| Dump after delayed branch scheduling. |
| |
| @item -fdump-rtl-dce1 |
| @itemx -fdump-rtl-dce2 |
| @opindex fdump-rtl-dce1 |
| @opindex fdump-rtl-dce2 |
| @option{-fdump-rtl-dce1} and @option{-fdump-rtl-dce2} enable dumping after |
| the two dead store elimination passes. |
| |
| @item -fdump-rtl-eh |
| @opindex fdump-rtl-eh |
| Dump after finalization of EH handling code. |
| |
| @item -fdump-rtl-eh_ranges |
| @opindex fdump-rtl-eh_ranges |
| Dump after conversion of EH handling range regions. |
| |
| @item -fdump-rtl-expand |
| @opindex fdump-rtl-expand |
| Dump after RTL generation. |
| |
| @item -fdump-rtl-fwprop1 |
| @itemx -fdump-rtl-fwprop2 |
| @opindex fdump-rtl-fwprop1 |
| @opindex fdump-rtl-fwprop2 |
| @option{-fdump-rtl-fwprop1} and @option{-fdump-rtl-fwprop2} enable |
| dumping after the two forward propagation passes. |
| |
| @item -fdump-rtl-gcse1 |
| @itemx -fdump-rtl-gcse2 |
| @opindex fdump-rtl-gcse1 |
| @opindex fdump-rtl-gcse2 |
| @option{-fdump-rtl-gcse1} and @option{-fdump-rtl-gcse2} enable dumping |
| after global common subexpression elimination. |
| |
| @item -fdump-rtl-init-regs |
| @opindex fdump-rtl-init-regs |
| Dump after the initialization of the registers. |
| |
| @item -fdump-rtl-initvals |
| @opindex fdump-rtl-initvals |
| Dump after the computation of the initial value sets. |
| |
| @itemx -fdump-rtl-into_cfglayout |
| @opindex fdump-rtl-into_cfglayout |
| Dump after converting to cfglayout mode. |
| |
| @item -fdump-rtl-ira |
| @opindex fdump-rtl-ira |
| Dump after iterated register allocation. |
| |
| @item -fdump-rtl-jump |
| @opindex fdump-rtl-jump |
| Dump after the second jump optimization. |
| |
| @item -fdump-rtl-loop2 |
| @opindex fdump-rtl-loop2 |
| @option{-fdump-rtl-loop2} enables dumping after the rtl |
| loop optimization passes. |
| |
| @item -fdump-rtl-mach |
| @opindex fdump-rtl-mach |
| Dump after performing the machine dependent reorganization pass, if that |
| pass exists. |
| |
| @item -fdump-rtl-mode_sw |
| @opindex fdump-rtl-mode_sw |
| Dump after removing redundant mode switches. |
| |
| @item -fdump-rtl-rnreg |
| @opindex fdump-rtl-rnreg |
| Dump after register renumbering. |
| |
| @itemx -fdump-rtl-outof_cfglayout |
| @opindex fdump-rtl-outof_cfglayout |
| Dump after converting from cfglayout mode. |
| |
| @item -fdump-rtl-peephole2 |
| @opindex fdump-rtl-peephole2 |
| Dump after the peephole pass. |
| |
| @item -fdump-rtl-postreload |
| @opindex fdump-rtl-postreload |
| Dump after post-reload optimizations. |
| |
| @itemx -fdump-rtl-pro_and_epilogue |
| @opindex fdump-rtl-pro_and_epilogue |
| Dump after generating the function prologues and epilogues. |
| |
| @item -fdump-rtl-regmove |
| @opindex fdump-rtl-regmove |
| Dump after the register move pass. |
| |
| @item -fdump-rtl-sched1 |
| @itemx -fdump-rtl-sched2 |
| @opindex fdump-rtl-sched1 |
| @opindex fdump-rtl-sched2 |
| @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2} enable dumping |
| after the basic block scheduling passes. |
| |
| @item -fdump-rtl-see |
| @opindex fdump-rtl-see |
| Dump after sign extension elimination. |
| |
| @item -fdump-rtl-seqabstr |
| @opindex fdump-rtl-seqabstr |
| Dump after common sequence discovery. |
| |
| @item -fdump-rtl-shorten |
| @opindex fdump-rtl-shorten |
| Dump after shortening branches. |
| |
| @item -fdump-rtl-sibling |
| @opindex fdump-rtl-sibling |
| Dump after sibling call optimizations. |
| |
| @item -fdump-rtl-split1 |
| @itemx -fdump-rtl-split2 |
| @itemx -fdump-rtl-split3 |
| @itemx -fdump-rtl-split4 |
| @itemx -fdump-rtl-split5 |
| @opindex fdump-rtl-split1 |
| @opindex fdump-rtl-split2 |
| @opindex fdump-rtl-split3 |
| @opindex fdump-rtl-split4 |
| @opindex fdump-rtl-split5 |
| @option{-fdump-rtl-split1}, @option{-fdump-rtl-split2}, |
| @option{-fdump-rtl-split3}, @option{-fdump-rtl-split4} and |
| @option{-fdump-rtl-split5} enable dumping after five rounds of |
| instruction splitting. |
| |
| @item -fdump-rtl-sms |
| @opindex fdump-rtl-sms |
| Dump after modulo scheduling. This pass is only run on some |
| architectures. |
| |
| @item -fdump-rtl-stack |
| @opindex fdump-rtl-stack |
| Dump after conversion from GCC's ``flat register file'' registers to the |
| x87's stack-like registers. This pass is only run on x86 variants. |
| |
| @item -fdump-rtl-subreg1 |
| @itemx -fdump-rtl-subreg2 |
| @opindex fdump-rtl-subreg1 |
| @opindex fdump-rtl-subreg2 |
| @option{-fdump-rtl-subreg1} and @option{-fdump-rtl-subreg2} enable dumping after |
| the two subreg expansion passes. |
| |
| @item -fdump-rtl-unshare |
| @opindex fdump-rtl-unshare |
| Dump after all rtl has been unshared. |
| |
| @item -fdump-rtl-vartrack |
| @opindex fdump-rtl-vartrack |
| Dump after variable tracking. |
| |
| @item -fdump-rtl-vregs |
| @opindex fdump-rtl-vregs |
| Dump after converting virtual registers to hard registers. |
| |
| @item -fdump-rtl-web |
| @opindex fdump-rtl-web |
| Dump after live range splitting. |
| |
| @item -fdump-rtl-regclass |
| @itemx -fdump-rtl-subregs_of_mode_init |
| @itemx -fdump-rtl-subregs_of_mode_finish |
| @itemx -fdump-rtl-dfinit |
| @itemx -fdump-rtl-dfinish |
| @opindex fdump-rtl-regclass |
| @opindex fdump-rtl-subregs_of_mode_init |
| @opindex fdump-rtl-subregs_of_mode_finish |
| @opindex fdump-rtl-dfinit |
| @opindex fdump-rtl-dfinish |
| These dumps are defined but always produce empty files. |
| |
| @item -da |
| @itemx -fdump-rtl-all |
| @opindex da |
| @opindex fdump-rtl-all |
| Produce all the dumps listed above. |
| |
| @item -dA |
| @opindex dA |
| Annotate the assembler output with miscellaneous debugging information. |
| |
| @item -dD |
| @opindex dD |
| Dump all macro definitions, at the end of preprocessing, in addition to |
| normal output. |
| |
| @item -dH |
| @opindex dH |
| Produce a core dump whenever an error occurs. |
| |
| @item -dp |
| @opindex dp |
| Annotate the assembler output with a comment indicating which |
| pattern and alternative is used. The length of each instruction is |
| also printed. |
| |
| @item -dP |
| @opindex dP |
| Dump the RTL in the assembler output as a comment before each instruction. |
| Also turns on @option{-dp} annotation. |
| |
| @item -dv |
| @opindex dv |
| For each of the other indicated dump files (@option{-fdump-rtl-@var{pass}}), |
| dump a representation of the control flow graph suitable for viewing with VCG |
| to @file{@var{file}.@var{pass}.vcg}. |
| |
| @item -dx |
| @opindex dx |
| Just generate RTL for a function instead of compiling it. Usually used |
| with @option{-fdump-rtl-expand}. |
| @end table |
| |
| @item -fdump-noaddr |
| @opindex fdump-noaddr |
| When doing debugging dumps, suppress address output. This makes it more |
| feasible to use diff on debugging dumps for compiler invocations with |
| different compiler binaries and/or different |
| text / bss / data / heap / stack / dso start locations. |
| |
| @item -fdump-unnumbered |
| @opindex fdump-unnumbered |
| When doing debugging dumps, suppress instruction numbers and address output. |
| This makes it more feasible to use diff on debugging dumps for compiler |
| invocations with different options, in particular with and without |
| @option{-g}. |
| |
| @item -fdump-unnumbered-links |
| @opindex fdump-unnumbered-links |
| When doing debugging dumps (see @option{-d} option above), suppress |
| instruction numbers for the links to the previous and next instructions |
| in a sequence. |
| |
| @item -fdump-translation-unit @r{(C++ only)} |
| @itemx -fdump-translation-unit-@var{options} @r{(C++ only)} |
| @opindex fdump-translation-unit |
| Dump a representation of the tree structure for the entire translation |
| unit to a file. The file name is made by appending @file{.tu} to the |
| source file name, and the file is created in the same directory as the |
| output file. If the @samp{-@var{options}} form is used, @var{options} |
| controls the details of the dump as described for the |
| @option{-fdump-tree} options. |
| |
| @item -fdump-class-hierarchy @r{(C++ only)} |
| @itemx -fdump-class-hierarchy-@var{options} @r{(C++ only)} |
| @opindex fdump-class-hierarchy |
| Dump a representation of each class's hierarchy and virtual function |
| table layout to a file. The file name is made by appending |
| @file{.class} to the source file name, and the file is created in the |
| same directory as the output file. If the @samp{-@var{options}} form |
| is used, @var{options} controls the details of the dump as described |
| for the @option{-fdump-tree} options. |
| |
| @item -fdump-ipa-@var{switch} |
| @opindex fdump-ipa |
| Control the dumping at various stages of inter-procedural analysis |
| language tree to a file. The file name is generated by appending a |
| switch specific suffix to the source file name, and the file is created |
| in the same directory as the output file. The following dumps are |
| possible: |
| |
| @table @samp |
| @item all |
| Enables all inter-procedural analysis dumps. |
| |
| @item cgraph |
| Dumps information about call-graph optimization, unused function removal, |
| and inlining decisions. |
| |
| @item inline |
| Dump after function inlining. |
| |
| @end table |
| |
| @item -fdump-passes |
| @opindex fdump-passes |
| Dump the list of optimization passes that are turned on and off by |
| the current command-line options. |
| |
| @item -fdump-statistics-@var{option} |
| @opindex fdump-statistics |
| Enable and control dumping of pass statistics in a separate file. The |
| file name is generated by appending a suffix ending in |
| @samp{.statistics} to the source file name, and the file is created in |
| the same directory as the output file. If the @samp{-@var{option}} |
| form is used, @samp{-stats} causes counters to be summed over the |
| whole compilation unit while @samp{-details} dumps every event as |
| the passes generate them. The default with no option is to sum |
| counters for each function compiled. |
| |
| @item -fdump-tree-@var{switch} |
| @itemx -fdump-tree-@var{switch}-@var{options} |
| @opindex fdump-tree |
| Control the dumping at various stages of processing the intermediate |
| language tree to a file. The file name is generated by appending a |
| switch-specific suffix to the source file name, and the file is |
| created in the same directory as the output file. If the |
| @samp{-@var{options}} form is used, @var{options} is a list of |
| @samp{-} separated options which control the details of the dump. Not |
| all options are applicable to all dumps; those that are not |
| meaningful are ignored. The following options are available |
| |
| @table @samp |
| @item address |
| Print the address of each node. Usually this is not meaningful as it |
| changes according to the environment and source file. Its primary use |
| is for tying up a dump file with a debug environment. |
| @item asmname |
| If @code{DECL_ASSEMBLER_NAME} has been set for a given decl, use that |
| in the dump instead of @code{DECL_NAME}. Its primary use is ease of |
| use working backward from mangled names in the assembly file. |
| @item slim |
| Inhibit dumping of members of a scope or body of a function merely |
| because that scope has been reached. Only dump such items when they |
| are directly reachable by some other path. When dumping pretty-printed |
| trees, this option inhibits dumping the bodies of control structures. |
| @item raw |
| Print a raw representation of the tree. By default, trees are |
| pretty-printed into a C-like representation. |
| @item details |
| Enable more detailed dumps (not honored by every dump option). |
| @item stats |
| Enable dumping various statistics about the pass (not honored by every dump |
| option). |
| @item blocks |
| Enable showing basic block boundaries (disabled in raw dumps). |
| @item vops |
| Enable showing virtual operands for every statement. |
| @item lineno |
| Enable showing line numbers for statements. |
| @item uid |
| Enable showing the unique ID (@code{DECL_UID}) for each variable. |
| @item verbose |
| Enable showing the tree dump for each statement. |
| @item eh |
| Enable showing the EH region number holding each statement. |
| @item scev |
| Enable showing scalar evolution analysis details. |
| @item all |
| Turn on all options, except @option{raw}, @option{slim}, @option{verbose} |
| and @option{lineno}. |
| @end table |
| |
| The following tree dumps are possible: |
| @table @samp |
| |
| @item original |
| @opindex fdump-tree-original |
| Dump before any tree based optimization, to @file{@var{file}.original}. |
| |
| @item optimized |
| @opindex fdump-tree-optimized |
| Dump after all tree based optimization, to @file{@var{file}.optimized}. |
| |
| @item gimple |
| @opindex fdump-tree-gimple |
| Dump each function before and after the gimplification pass to a file. The |
| file name is made by appending @file{.gimple} to the source file name. |
| |
| @item cfg |
| @opindex fdump-tree-cfg |
| Dump the control flow graph of each function to a file. The file name is |
| made by appending @file{.cfg} to the source file name. |
| |
| @item vcg |
| @opindex fdump-tree-vcg |
| Dump the control flow graph of each function to a file in VCG format. The |
| file name is made by appending @file{.vcg} to the source file name. Note |
| that if the file contains more than one function, the generated file cannot |
| be used directly by VCG@. You must cut and paste each function's |
| graph into its own separate file first. |
| |
| @item ch |
| @opindex fdump-tree-ch |
| Dump each function after copying loop headers. The file name is made by |
| appending @file{.ch} to the source file name. |
| |
| @item ssa |
| @opindex fdump-tree-ssa |
| Dump SSA related information to a file. The file name is made by appending |
| @file{.ssa} to the source file name. |
| |
| @item alias |
| @opindex fdump-tree-alias |
| Dump aliasing information for each function. The file name is made by |
| appending @file{.alias} to the source file name. |
| |
| @item ccp |
| @opindex fdump-tree-ccp |
| Dump each function after CCP@. The file name is made by appending |
| @file{.ccp} to the source file name. |
| |
| @item storeccp |
| @opindex fdump-tree-storeccp |
| Dump each function after STORE-CCP@. The file name is made by appending |
| @file{.storeccp} to the source file name. |
| |
| @item pre |
| @opindex fdump-tree-pre |
| Dump trees after partial redundancy elimination. The file name is made |
| by appending @file{.pre} to the source file name. |
| |
| @item fre |
| @opindex fdump-tree-fre |
| Dump trees after full redundancy elimination. The file name is made |
| by appending @file{.fre} to the source file name. |
| |
| @item copyprop |
| @opindex fdump-tree-copyprop |
| Dump trees after copy propagation. The file name is made |
| by appending @file{.copyprop} to the source file name. |
| |
| @item store_copyprop |
| @opindex fdump-tree-store_copyprop |
| Dump trees after store copy-propagation. The file name is made |
| by appending @file{.store_copyprop} to the source file name. |
| |
| @item dce |
| @opindex fdump-tree-dce |
| Dump each function after dead code elimination. The file name is made by |
| appending @file{.dce} to the source file name. |
| |
| @item mudflap |
| @opindex fdump-tree-mudflap |
| Dump each function after adding mudflap instrumentation. The file name is |
| made by appending @file{.mudflap} to the source file name. |
| |
| @item sra |
| @opindex fdump-tree-sra |
| Dump each function after performing scalar replacement of aggregates. The |
| file name is made by appending @file{.sra} to the source file name. |
| |
| @item sink |
| @opindex fdump-tree-sink |
| Dump each function after performing code sinking. The file name is made |
| by appending @file{.sink} to the source file name. |
| |
| @item dom |
| @opindex fdump-tree-dom |
| Dump each function after applying dominator tree optimizations. The file |
| name is made by appending @file{.dom} to the source file name. |
| |
| @item dse |
| @opindex fdump-tree-dse |
| Dump each function after applying dead store elimination. The file |
| name is made by appending @file{.dse} to the source file name. |
| |
| @item phiopt |
| @opindex fdump-tree-phiopt |
| Dump each function after optimizing PHI nodes into straightline code. The file |
| name is made by appending @file{.phiopt} to the source file name. |
| |
| @item forwprop |
| @opindex fdump-tree-forwprop |
| Dump each function after forward propagating single use variables. The file |
| name is made by appending @file{.forwprop} to the source file name. |
| |
| @item copyrename |
| @opindex fdump-tree-copyrename |
| Dump each function after applying the copy rename optimization. The file |
| name is made by appending @file{.copyrename} to the source file name. |
| |
| @item nrv |
| @opindex fdump-tree-nrv |
| Dump each function after applying the named return value optimization on |
| generic trees. The file name is made by appending @file{.nrv} to the source |
| file name. |
| |
| @item vect |
| @opindex fdump-tree-vect |
| Dump each function after applying vectorization of loops. The file name is |
| made by appending @file{.vect} to the source file name. |
| |
| @item slp |
| @opindex fdump-tree-slp |
| Dump each function after applying vectorization of basic blocks. The file name |
| is made by appending @file{.slp} to the source file name. |
| |
| @item vrp |
| @opindex fdump-tree-vrp |
| Dump each function after Value Range Propagation (VRP). The file name |
| is made by appending @file{.vrp} to the source file name. |
| |
| @item all |
| @opindex fdump-tree-all |
| Enable all the available tree dumps with the flags provided in this option. |
| @end table |
| |
| @item -ftree-vectorizer-verbose=@var{n} |
| @opindex ftree-vectorizer-verbose |
| This option controls the amount of debugging output the vectorizer prints. |
| This information is written to standard error, unless |
| @option{-fdump-tree-all} or @option{-fdump-tree-vect} is specified, |
| in which case it is output to the usual dump listing file, @file{.vect}. |
| For @var{n}=0 no diagnostic information is reported. |
| If @var{n}=1 the vectorizer reports each loop that got vectorized, |
| and the total number of loops that got vectorized. |
| If @var{n}=2 the vectorizer also reports non-vectorized loops that passed |
| the first analysis phase (vect_analyze_loop_form) - i.e.@: countable, |
| inner-most, single-bb, single-entry/exit loops. This is the same verbosity |
| level that @option{-fdump-tree-vect-stats} uses. |
| Higher verbosity levels mean either more information dumped for each |
| reported loop, or same amount of information reported for more loops: |
| if @var{n}=3, vectorizer cost model information is reported. |
| If @var{n}=4, alignment related information is added to the reports. |
| If @var{n}=5, data-references related information (e.g.@: memory dependences, |
| memory access-patterns) is added to the reports. |
| If @var{n}=6, the vectorizer reports also non-vectorized inner-most loops |
| that did not pass the first analysis phase (i.e., may not be countable, or |
| may have complicated control-flow). |
| If @var{n}=7, the vectorizer reports also non-vectorized nested loops. |
| If @var{n}=8, SLP related information is added to the reports. |
| For @var{n}=9, all the information the vectorizer generates during its |
| analysis and transformation is reported. This is the same verbosity level |
| that @option{-fdump-tree-vect-details} uses. |
| |
| @item -frandom-seed=@var{string} |
| @opindex frandom-seed |
| This option provides a seed that GCC uses in place of |
| random numbers in generating certain symbol names |
| that have to be different in every compiled file. It is also used to |
| place unique stamps in coverage data files and the object files that |
| produce them. You can use the @option{-frandom-seed} option to produce |
| reproducibly identical object files. |
| |
| The @var{string} should be different for every file you compile. |
| |
| @item -fsched-verbose=@var{n} |
| @opindex fsched-verbose |
| On targets that use instruction scheduling, this option controls the |
| amount of debugging output the scheduler prints. This information is |
| written to standard error, unless @option{-fdump-rtl-sched1} or |
| @option{-fdump-rtl-sched2} is specified, in which case it is output |
| to the usual dump listing file, @file{.sched1} or @file{.sched2} |
| respectively. However for @var{n} greater than nine, the output is |
| always printed to standard error. |
| |
| For @var{n} greater than zero, @option{-fsched-verbose} outputs the |
| same information as @option{-fdump-rtl-sched1} and @option{-fdump-rtl-sched2}. |
| For @var{n} greater than one, it also output basic block probabilities, |
| detailed ready list information and unit/insn info. For @var{n} greater |
| than two, it includes RTL at abort point, control-flow and regions info. |
| And for @var{n} over four, @option{-fsched-verbose} also includes |
| dependence info. |
| |
| @item -save-temps |
| @itemx -save-temps=cwd |
| @opindex save-temps |
| Store the usual ``temporary'' intermediate files permanently; place them |
| in the current directory and name them based on the source file. Thus, |
| compiling @file{foo.c} with @option{-c -save-temps} produces files |
| @file{foo.i} and @file{foo.s}, as well as @file{foo.o}. This creates a |
| preprocessed @file{foo.i} output file even though the compiler now |
| normally uses an integrated preprocessor. |
| |
| When used in combination with the @option{-x} command-line option, |
| @option{-save-temps} is sensible enough to avoid over writing an |
| input source file with the same extension as an intermediate file. |
| The corresponding intermediate file may be obtained by renaming the |
| source file before using @option{-save-temps}. |
| |
| If you invoke GCC in parallel, compiling several different source |
| files that share a common base name in different subdirectories or the |
| same source file compiled for multiple output destinations, it is |
| likely that the different parallel compilers will interfere with each |
| other, and overwrite the temporary files. For instance: |
| |
| @smallexample |
| gcc -save-temps -o outdir1/foo.o indir1/foo.c& |
| gcc -save-temps -o outdir2/foo.o indir2/foo.c& |
| @end smallexample |
| |
| may result in @file{foo.i} and @file{foo.o} being written to |
| simultaneously by both compilers. |
| |
| @item -save-temps=obj |
| @opindex save-temps=obj |
| Store the usual ``temporary'' intermediate files permanently. If the |
| @option{-o} option is used, the temporary files are based on the |
| object file. If the @option{-o} option is not used, the |
| @option{-save-temps=obj} switch behaves like @option{-save-temps}. |
| |
| For example: |
| |
| @smallexample |
| gcc -save-temps=obj -c foo.c |
| gcc -save-temps=obj -c bar.c -o dir/xbar.o |
| gcc -save-temps=obj foobar.c -o dir2/yfoobar |
| @end smallexample |
| |
| @noindent |
| creates @file{foo.i}, @file{foo.s}, @file{dir/xbar.i}, |
| @file{dir/xbar.s}, @file{dir2/yfoobar.i}, @file{dir2/yfoobar.s}, and |
| @file{dir2/yfoobar.o}. |
| |
| @item -time@r{[}=@var{file}@r{]} |
| @opindex time |
| Report the CPU time taken by each subprocess in the compilation |
| sequence. For C source files, this is the compiler proper and assembler |
| (plus the linker if linking is done). |
| |
| Without the specification of an output file, the output looks like this: |
| |
| @smallexample |
| # cc1 0.12 0.01 |
| # as 0.00 0.01 |
| @end smallexample |
| |
| The first number on each line is the ``user time'', that is time spent |
| executing the program itself. The second number is ``system time'', |
| time spent executing operating system routines on behalf of the program. |
| Both numbers are in seconds. |
| |
| With the specification of an output file, the output is appended to the |
| named file, and it looks like this: |
| |
| @smallexample |
| 0.12 0.01 cc1 @var{options} |
| 0.00 0.01 as @var{options} |
| @end smallexample |
| |
| The ``user time'' and the ``system time'' are moved before the program |
| name, and the options passed to the program are displayed, so that one |
| can later tell what file was being compiled, and with which options. |
| |
| @item -fvar-tracking |
| @opindex fvar-tracking |
| Run variable tracking pass. It computes where variables are stored at each |
| position in code. Better debugging information is then generated |
| (if the debugging information format supports this information). |
| |
| It is enabled by default when compiling with optimization (@option{-Os}, |
| @option{-O}, @option{-O2}, @dots{}), debugging information (@option{-g}) and |
| the debug info format supports it. |
| |
| @item -fvar-tracking-assignments |
| @opindex fvar-tracking-assignments |
| @opindex fno-var-tracking-assignments |
| Annotate assignments to user variables early in the compilation and |
| attempt to carry the annotations over throughout the compilation all the |
| way to the end, in an attempt to improve debug information while |
| optimizing. Use of @option{-gdwarf-4} is recommended along with it. |
| |
| It can be enabled even if var-tracking is disabled, in which case |
| annotations are created and maintained, but discarded at the end. |
| |
| @item -fvar-tracking-assignments-toggle |
| @opindex fvar-tracking-assignments-toggle |
| @opindex fno-var-tracking-assignments-toggle |
| Toggle @option{-fvar-tracking-assignments}, in the same way that |
| @option{-gtoggle} toggles @option{-g}. |
| |
| @item -print-file-name=@var{library} |
| @opindex print-file-name |
| Print the full absolute name of the library file @var{library} that |
| would be used when linking---and don't do anything else. With this |
| option, GCC does not compile or link anything; it just prints the |
| file name. |
| |
| @item -print-multi-directory |
| @opindex print-multi-directory |
| Print the directory name corresponding to the multilib selected by any |
| other switches present in the command line. This directory is supposed |
| to exist in @env{GCC_EXEC_PREFIX}. |
| |
| @item -print-multi-lib |
| @opindex print-multi-lib |
| Print the mapping from multilib directory names to compiler switches |
| that enable them. The directory name is separated from the switches by |
| @samp{;}, and each switch starts with an @samp{@@} instead of the |
| @samp{-}, without spaces between multiple switches. This is supposed to |
| ease shell processing. |
| |
| @item -print-multi-os-directory |
| @opindex print-multi-os-directory |
| Print the path to OS libraries for the selected |
| multilib, relative to some @file{lib} subdirectory. If OS libraries are |
| present in the @file{lib} subdirectory and no multilibs are used, this is |
| usually just @file{.}, if OS libraries are present in @file{lib@var{suffix}} |
| sibling directories this prints e.g.@: @file{../lib64}, @file{../lib} or |
| @file{../lib32}, or if OS libraries are present in @file{lib/@var{subdir}} |
| subdirectories it prints e.g.@: @file{amd64}, @file{sparcv9} or @file{ev6}. |
| |
| @item -print-prog-name=@var{program} |
| @opindex print-prog-name |
| Like @option{-print-file-name}, but searches for a program such as @samp{cpp}. |
| |
| @item -print-libgcc-file-name |
| @opindex print-libgcc-file-name |
| Same as @option{-print-file-name=libgcc.a}. |
| |
| This is useful when you use @option{-nostdlib} or @option{-nodefaultlibs} |
| but you do want to link with @file{libgcc.a}. You can do: |
| |
| @smallexample |
| gcc -nostdlib @var{files}@dots{} `gcc -print-libgcc-file-name` |
| @end smallexample |
| |
| @item -print-search-dirs |
| @opindex print-search-dirs |
| Print the name of the configured installation directory and a list of |
| program and library directories @command{gcc} searches---and don't do anything else. |
| |
| This is useful when @command{gcc} prints the error message |
| @samp{installation problem, cannot exec cpp0: No such file or directory}. |
| To resolve this you either need to put @file{cpp0} and the other compiler |
| components where @command{gcc} expects to find them, or you can set the environment |
| variable @env{GCC_EXEC_PREFIX} to the directory where you installed them. |
| Don't forget the trailing @samp{/}. |
| @xref{Environment Variables}. |
| |
| @item -print-sysroot |
| @opindex print-sysroot |
| Print the target sysroot directory that is used during |
| compilation. This is the target sysroot specified either at configure |
| time or using the @option{--sysroot} option, possibly with an extra |
| suffix that depends on compilation options. If no target sysroot is |
| specified, the option prints nothing. |
| |
| @item -print-sysroot-headers-suffix |
| @opindex print-sysroot-headers-suffix |
| Print the suffix added to the target sysroot when searching for |
| headers, or give an error if the compiler is not configured with such |
| a suffix---and don't do anything else. |
| |
| @item -dumpmachine |
| @opindex dumpmachine |
| Print the compiler's target machine (for example, |
| @samp{i686-pc-linux-gnu})---and don't do anything else. |
| |
| @item -dumpversion |
| @opindex dumpversion |
| Print the compiler version (for example, @samp{3.0})---and don't do |
| anything else. |
| |
| @item -dumpspecs |
| @opindex dumpspecs |
| Print the compiler's built-in specs---and don't do anything else. (This |
| is used when GCC itself is being built.) @xref{Spec Files}. |
| |
| @item -fno-eliminate-unused-debug-types |
| @opindex feliminate-unused-debug-types |
| @opindex fno-eliminate-unused-debug-types |
| Normally, when producing DWARF 2 output, GCC avoids producing debug symbol |
| output for types that are nowhere used in the source file being compiled. |
| Sometimes it is useful to have GCC emit debugging |
| information for all types declared in a compilation |
| unit, regardless of whether or not they are actually used |
| in that compilation unit, for example |
| if, in the debugger, you want to cast a value to a type that is |
| not actually used in your program (but is declared). More often, |
| however, this results in a significant amount of wasted space. |
| @end table |
| |
| @node Optimize Options |
| @section Options That Control Optimization |
| @cindex optimize options |
| @cindex options, optimization |
| |
| These options control various sorts of optimizations. |
| |
| Without any optimization option, the compiler's goal is to reduce the |
| cost of compilation and to make debugging produce the expected |
| results. Statements are independent: if you stop the program with a |
| breakpoint between statements, you can then assign a new value to any |
| variable or change the program counter to any other statement in the |
| function and get exactly the results you expect from the source |
| code. |
| |
| Turning on optimization flags makes the compiler attempt to improve |
| the performance and/or code size at the expense of compilation time |
| and possibly the ability to debug the program. |
| |
| The compiler performs optimization based on the knowledge it has of the |
| program. Compiling multiple files at once to a single output file mode allows |
| the compiler to use information gained from all of the files when compiling |
| each of them. |
| |
| Not all optimizations are controlled directly by a flag. Only |
| optimizations that have a flag are listed in this section. |
| |
| Most optimizations are only enabled if an @option{-O} level is set on |
| the command line. Otherwise they are disabled, even if individual |
| optimization flags are specified. |
| |
| Depending on the target and how GCC was configured, a slightly different |
| set of optimizations may be enabled at each @option{-O} level than |
| those listed here. You can invoke GCC with @option{-Q --help=optimizers} |
| to find out the exact set of optimizations that are enabled at each level. |
| @xref{Overall Options}, for examples. |
| |
| @table @gcctabopt |
| @item -O |
| @itemx -O1 |
| @opindex O |
| @opindex O1 |
| Optimize. Optimizing compilation takes somewhat more time, and a lot |
| more memory for a large function. |
| |
| With @option{-O}, the compiler tries to reduce code size and execution |
| time, without performing any optimizations that take a great deal of |
| compilation time. |
| |
| @option{-O} turns on the following optimization flags: |
| @gccoptlist{ |
| -fauto-inc-dec @gol |
| -fcompare-elim @gol |
| -fcprop-registers @gol |
| -fdce @gol |
| -fdefer-pop @gol |
| -fdelayed-branch @gol |
| -fdse @gol |
| -fguess-branch-probability @gol |
| -fif-conversion2 @gol |
| -fif-conversion @gol |
| -fipa-pure-const @gol |
| -fipa-profile @gol |
| -fipa-reference @gol |
| -fmerge-constants |
| -fsplit-wide-types @gol |
| -ftree-bit-ccp @gol |
| -ftree-builtin-call-dce @gol |
| -ftree-ccp @gol |
| -ftree-ch @gol |
| -ftree-copyrename @gol |
| -ftree-dce @gol |
| -ftree-dominator-opts @gol |
| -ftree-dse @gol |
| -ftree-forwprop @gol |
| -ftree-fre @gol |
| -ftree-phiprop @gol |
| -ftree-slsr @gol |
| -ftree-sra @gol |
| -ftree-pta @gol |
| -ftree-ter @gol |
| -funit-at-a-time} |
| |
| @option{-O} also turns on @option{-fomit-frame-pointer} on machines |
| where doing so does not interfere with debugging. |
| |
| @item -O2 |
| @opindex O2 |
| Optimize even more. GCC performs nearly all supported optimizations |
| that do not involve a space-speed tradeoff. |
| As compared to @option{-O}, this option increases both compilation time |
| and the performance of the generated code. |
| |
| @option{-O2} turns on all optimization flags specified by @option{-O}. It |
| also turns on the following optimization flags: |
| @gccoptlist{-fthread-jumps @gol |
| -falign-functions -falign-jumps @gol |
| -falign-loops -falign-labels @gol |
| -fcaller-saves @gol |
| -fcrossjumping @gol |
| -fcse-follow-jumps -fcse-skip-blocks @gol |
| -fdelete-null-pointer-checks @gol |
| -fdevirtualize @gol |
| -fexpensive-optimizations @gol |
| -fgcse -fgcse-lm @gol |
| -fhoist-adjacent-loads @gol |
| -finline-small-functions @gol |
| -findirect-inlining @gol |
| -fipa-sra @gol |
| -foptimize-sibling-calls @gol |
| -fpartial-inlining @gol |
| -fpeephole2 @gol |
| -fregmove @gol |
| -freorder-blocks -freorder-functions @gol |
| -frerun-cse-after-loop @gol |
| -fsched-interblock -fsched-spec @gol |
| -fschedule-insns -fschedule-insns2 @gol |
| -fstrict-aliasing -fstrict-overflow @gol |
| -ftree-switch-conversion -ftree-tail-merge @gol |
| -ftree-pre @gol |
| -ftree-vrp} |
| |
| Please note the warning under @option{-fgcse} about |
| invoking @option{-O2} on programs that use computed gotos. |
| |
| @item -O3 |
| @opindex O3 |
| Optimize yet more. @option{-O3} turns on all optimizations specified |
| by @option{-O2} and also turns on the @option{-finline-functions}, |
| @option{-funswitch-loops}, @option{-fpredictive-commoning}, |
| @option{-fgcse-after-reload}, @option{-ftree-vectorize}, |
| @option{-fvect-cost-model}, |
| @option{-ftree-partial-pre} and @option{-fipa-cp-clone} options. |
| |
| @item -O0 |
| @opindex O0 |
| Reduce compilation time and make debugging produce the expected |
| results. This is the default. |
| |
| @item -Os |
| @opindex Os |
| Optimize for size. @option{-Os} enables all @option{-O2} optimizations that |
| do not typically increase code size. It also performs further |
| optimizations designed to reduce code size. |
| |
| @option{-Os} disables the following optimization flags: |
| @gccoptlist{-falign-functions -falign-jumps -falign-loops @gol |
| -falign-labels -freorder-blocks -freorder-blocks-and-partition @gol |
| -fprefetch-loop-arrays -ftree-vect-loop-version} |
| |
| @item -Ofast |
| @opindex Ofast |
| Disregard strict standards compliance. @option{-Ofast} enables all |
| @option{-O3} optimizations. It also enables optimizations that are not |
| valid for all standard-compliant programs. |
| It turns on @option{-ffast-math} and the Fortran-specific |
| @option{-fno-protect-parens} and @option{-fstack-arrays}. |
| |
| @item -Og |
| @opindex Og |
| Optimize debugging experience. @option{-Og} enables optimizations |
| that do not interfere with debugging. It should be the optimization |
| level of choice for the standard edit-compile-debug cycle, offering |
| a reasonable level of optimization while maintaining fast compilation |
| and a good debugging experience. |
| |
| If you use multiple @option{-O} options, with or without level numbers, |
| the last such option is the one that is effective. |
| @end table |
| |
| Options of the form @option{-f@var{flag}} specify machine-independent |
| flags. Most flags have both positive and negative forms; the negative |
| form of @option{-ffoo} is @option{-fno-foo}. In the table |
| below, only one of the forms is listed---the one you typically |
| use. You can figure out the other form by either removing @samp{no-} |
| or adding it. |
| |
| The following options control specific optimizations. They are either |
| activated by @option{-O} options or are related to ones that are. You |
| can use the following flags in the rare cases when ``fine-tuning'' of |
| optimizations to be performed is desired. |
| |
| @table @gcctabopt |
| @item -fno-default-inline |
| @opindex fno-default-inline |
| Do not make member functions inline by default merely because they are |
| defined inside the class scope (C++ only). Otherwise, when you specify |
| @w{@option{-O}}, member functions defined inside class scope are compiled |
| inline by default; i.e., you don't need to add @samp{inline} in front of |
| the member function name. |
| |
| @item -fno-defer-pop |
| @opindex fno-defer-pop |
| Always pop the arguments to each function call as soon as that function |
| returns. For machines that must pop arguments after a function call, |
| the compiler normally lets arguments accumulate on the stack for several |
| function calls and pops them all at once. |
| |
| Disabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fforward-propagate |
| @opindex fforward-propagate |
| Perform a forward propagation pass on RTL@. The pass tries to combine two |
| instructions and checks if the result can be simplified. If loop unrolling |
| is active, two passes are performed and the second is scheduled after |
| loop unrolling. |
| |
| This option is enabled by default at optimization levels @option{-O}, |
| @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -ffp-contract=@var{style} |
| @opindex ffp-contract |
| @option{-ffp-contract=off} disables floating-point expression contraction. |
| @option{-ffp-contract=fast} enables floating-point expression contraction |
| such as forming of fused multiply-add operations if the target has |
| native support for them. |
| @option{-ffp-contract=on} enables floating-point expression contraction |
| if allowed by the language standard. This is currently not implemented |
| and treated equal to @option{-ffp-contract=off}. |
| |
| The default is @option{-ffp-contract=fast}. |
| |
| @item -fomit-frame-pointer |
| @opindex fomit-frame-pointer |
| Don't keep the frame pointer in a register for functions that |
| don't need one. This avoids the instructions to save, set up and |
| restore frame pointers; it also makes an extra register available |
| in many functions. @strong{It also makes debugging impossible on |
| some machines.} |
| |
| On some machines, such as the VAX, this flag has no effect, because |
| the standard calling sequence automatically handles the frame pointer |
| and nothing is saved by pretending it doesn't exist. The |
| machine-description macro @code{FRAME_POINTER_REQUIRED} controls |
| whether a target machine supports this flag. @xref{Registers,,Register |
| Usage, gccint, GNU Compiler Collection (GCC) Internals}. |
| |
| Starting with GCC version 4.6, the default setting (when not optimizing for |
| size) for 32-bit GNU/Linux x86 and 32-bit Darwin x86 targets has been changed to |
| @option{-fomit-frame-pointer}. The default can be reverted to |
| @option{-fno-omit-frame-pointer} by configuring GCC with the |
| @option{--enable-frame-pointer} configure option. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -foptimize-sibling-calls |
| @opindex foptimize-sibling-calls |
| Optimize sibling and tail recursive calls. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fno-inline |
| @opindex fno-inline |
| Do not expand any functions inline apart from those marked with |
| the @code{always_inline} attribute. This is the default when not |
| optimizing. |
| |
| Single functions can be exempted from inlining by marking them |
| with the @code{noinline} attribute. |
| |
| @item -finline-small-functions |
| @opindex finline-small-functions |
| Integrate functions into their callers when their body is smaller than expected |
| function call code (so overall size of program gets smaller). The compiler |
| heuristically decides which functions are simple enough to be worth integrating |
| in this way. This inlining applies to all functions, even those not declared |
| inline. |
| |
| Enabled at level @option{-O2}. |
| |
| @item -findirect-inlining |
| @opindex findirect-inlining |
| Inline also indirect calls that are discovered to be known at compile |
| time thanks to previous inlining. This option has any effect only |
| when inlining itself is turned on by the @option{-finline-functions} |
| or @option{-finline-small-functions} options. |
| |
| Enabled at level @option{-O2}. |
| |
| @item -finline-functions |
| @opindex finline-functions |
| Consider all functions for inlining, even if they are not declared inline. |
| The compiler heuristically decides which functions are worth integrating |
| in this way. |
| |
| If all calls to a given function are integrated, and the function is |
| declared @code{static}, then the function is normally not output as |
| assembler code in its own right. |
| |
| Enabled at level @option{-O3}. |
| |
| @item -finline-functions-called-once |
| @opindex finline-functions-called-once |
| Consider all @code{static} functions called once for inlining into their |
| caller even if they are not marked @code{inline}. If a call to a given |
| function is integrated, then the function is not output as assembler code |
| in its own right. |
| |
| Enabled at levels @option{-O1}, @option{-O2}, @option{-O3} and @option{-Os}. |
| |
| @item -fearly-inlining |
| @opindex fearly-inlining |
| Inline functions marked by @code{always_inline} and functions whose body seems |
| smaller than the function call overhead early before doing |
| @option{-fprofile-generate} instrumentation and real inlining pass. Doing so |
| makes profiling significantly cheaper and usually inlining faster on programs |
| having large chains of nested wrapper functions. |
| |
| Enabled by default. |
| |
| @item -fipa-sra |
| @opindex fipa-sra |
| Perform interprocedural scalar replacement of aggregates, removal of |
| unused parameters and replacement of parameters passed by reference |
| by parameters passed by value. |
| |
| Enabled at levels @option{-O2}, @option{-O3} and @option{-Os}. |
| |
| @item -finline-limit=@var{n} |
| @opindex finline-limit |
| By default, GCC limits the size of functions that can be inlined. This flag |
| allows coarse control of this limit. @var{n} is the size of functions that |
| can be inlined in number of pseudo instructions. |
| |
| Inlining is actually controlled by a number of parameters, which may be |
| specified individually by using @option{--param @var{name}=@var{value}}. |
| The @option{-finline-limit=@var{n}} option sets some of these parameters |
| as follows: |
| |
| @table @gcctabopt |
| @item max-inline-insns-single |
| is set to @var{n}/2. |
| @item max-inline-insns-auto |
| is set to @var{n}/2. |
| @end table |
| |
| See below for a documentation of the individual |
| parameters controlling inlining and for the defaults of these parameters. |
| |
| @emph{Note:} there may be no value to @option{-finline-limit} that results |
| in default behavior. |
| |
| @emph{Note:} pseudo instruction represents, in this particular context, an |
| abstract measurement of function's size. In no way does it represent a count |
| of assembly instructions and as such its exact meaning might change from one |
| release to an another. |
| |
| @item -fno-keep-inline-dllexport |
| @opindex -fno-keep-inline-dllexport |
| This is a more fine-grained version of @option{-fkeep-inline-functions}, |
| which applies only to functions that are declared using the @code{dllexport} |
| attribute or declspec (@xref{Function Attributes,,Declaring Attributes of |
| Functions}.) |
| |
| @item -fkeep-inline-functions |
| @opindex fkeep-inline-functions |
| In C, emit @code{static} functions that are declared @code{inline} |
| into the object file, even if the function has been inlined into all |
| of its callers. This switch does not affect functions using the |
| @code{extern inline} extension in GNU C90@. In C++, emit any and all |
| inline functions into the object file. |
| |
| @item -fkeep-static-consts |
| @opindex fkeep-static-consts |
| Emit variables declared @code{static const} when optimization isn't turned |
| on, even if the variables aren't referenced. |
| |
| GCC enables this option by default. If you want to force the compiler to |
| check if a variable is referenced, regardless of whether or not |
| optimization is turned on, use the @option{-fno-keep-static-consts} option. |
| |
| @item -fmerge-constants |
| @opindex fmerge-constants |
| Attempt to merge identical constants (string constants and floating-point |
| constants) across compilation units. |
| |
| This option is the default for optimized compilation if the assembler and |
| linker support it. Use @option{-fno-merge-constants} to inhibit this |
| behavior. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fmerge-all-constants |
| @opindex fmerge-all-constants |
| Attempt to merge identical constants and identical variables. |
| |
| This option implies @option{-fmerge-constants}. In addition to |
| @option{-fmerge-constants} this considers e.g.@: even constant initialized |
| arrays or initialized constant variables with integral or floating-point |
| types. Languages like C or C++ require each variable, including multiple |
| instances of the same variable in recursive calls, to have distinct locations, |
| so using this option results in non-conforming |
| behavior. |
| |
| @item -fmodulo-sched |
| @opindex fmodulo-sched |
| Perform swing modulo scheduling immediately before the first scheduling |
| pass. This pass looks at innermost loops and reorders their |
| instructions by overlapping different iterations. |
| |
| @item -fmodulo-sched-allow-regmoves |
| @opindex fmodulo-sched-allow-regmoves |
| Perform more aggressive SMS-based modulo scheduling with register moves |
| allowed. By setting this flag certain anti-dependences edges are |
| deleted, which triggers the generation of reg-moves based on the |
| life-range analysis. This option is effective only with |
| @option{-fmodulo-sched} enabled. |
| |
| @item -fno-branch-count-reg |
| @opindex fno-branch-count-reg |
| Do not use ``decrement and branch'' instructions on a count register, |
| but instead generate a sequence of instructions that decrement a |
| register, compare it against zero, then branch based upon the result. |
| This option is only meaningful on architectures that support such |
| instructions, which include x86, PowerPC, IA-64 and S/390. |
| |
| The default is @option{-fbranch-count-reg}. |
| |
| @item -fno-function-cse |
| @opindex fno-function-cse |
| Do not put function addresses in registers; make each instruction that |
| calls a constant function contain the function's address explicitly. |
| |
| This option results in less efficient code, but some strange hacks |
| that alter the assembler output may be confused by the optimizations |
| performed when this option is not used. |
| |
| The default is @option{-ffunction-cse} |
| |
| @item -fno-zero-initialized-in-bss |
| @opindex fno-zero-initialized-in-bss |
| If the target supports a BSS section, GCC by default puts variables that |
| are initialized to zero into BSS@. This can save space in the resulting |
| code. |
| |
| This option turns off this behavior because some programs explicitly |
| rely on variables going to the data section---e.g., so that the |
| resulting executable can find the beginning of that section and/or make |
| assumptions based on that. |
| |
| The default is @option{-fzero-initialized-in-bss}. |
| |
| @item -fmudflap -fmudflapth -fmudflapir |
| @opindex fmudflap |
| @opindex fmudflapth |
| @opindex fmudflapir |
| @cindex bounds checking |
| @cindex mudflap |
| For front-ends that support it (C and C++), instrument all risky |
| pointer/array dereferencing operations, some standard library |
| string/heap functions, and some other associated constructs with |
| range/validity tests. Modules so instrumented should be immune to |
| buffer overflows, invalid heap use, and some other classes of C/C++ |
| programming errors. The instrumentation relies on a separate runtime |
| library (@file{libmudflap}), which is linked into a program if |
| @option{-fmudflap} is given at link time. Run-time behavior of the |
| instrumented program is controlled by the @env{MUDFLAP_OPTIONS} |
| environment variable. See @code{env MUDFLAP_OPTIONS=-help a.out} |
| for its options. |
| |
| Use @option{-fmudflapth} instead of @option{-fmudflap} to compile and to |
| link if your program is multi-threaded. Use @option{-fmudflapir}, in |
| addition to @option{-fmudflap} or @option{-fmudflapth}, if |
| instrumentation should ignore pointer reads. This produces less |
| instrumentation (and therefore faster execution) and still provides |
| some protection against outright memory corrupting writes, but allows |
| erroneously read data to propagate within a program. |
| |
| @item -fthread-jumps |
| @opindex fthread-jumps |
| Perform optimizations that check to see if a jump branches to a |
| location where another comparison subsumed by the first is found. If |
| so, the first branch is redirected to either the destination of the |
| second branch or a point immediately following it, depending on whether |
| the condition is known to be true or false. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fsplit-wide-types |
| @opindex fsplit-wide-types |
| When using a type that occupies multiple registers, such as @code{long |
| long} on a 32-bit system, split the registers apart and allocate them |
| independently. This normally generates better code for those types, |
| but may make debugging more difficult. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, |
| @option{-Os}. |
| |
| @item -fcse-follow-jumps |
| @opindex fcse-follow-jumps |
| In common subexpression elimination (CSE), scan through jump instructions |
| when the target of the jump is not reached by any other path. For |
| example, when CSE encounters an @code{if} statement with an |
| @code{else} clause, CSE follows the jump when the condition |
| tested is false. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcse-skip-blocks |
| @opindex fcse-skip-blocks |
| This is similar to @option{-fcse-follow-jumps}, but causes CSE to |
| follow jumps that conditionally skip over blocks. When CSE |
| encounters a simple @code{if} statement with no else clause, |
| @option{-fcse-skip-blocks} causes CSE to follow the jump around the |
| body of the @code{if}. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -frerun-cse-after-loop |
| @opindex frerun-cse-after-loop |
| Re-run common subexpression elimination after loop optimizations are |
| performed. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fgcse |
| @opindex fgcse |
| Perform a global common subexpression elimination pass. |
| This pass also performs global constant and copy propagation. |
| |
| @emph{Note:} When compiling a program using computed gotos, a GCC |
| extension, you may get better run-time performance if you disable |
| the global common subexpression elimination pass by adding |
| @option{-fno-gcse} to the command line. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fgcse-lm |
| @opindex fgcse-lm |
| When @option{-fgcse-lm} is enabled, global common subexpression elimination |
| attempts to move loads that are only killed by stores into themselves. This |
| allows a loop containing a load/store sequence to be changed to a load outside |
| the loop, and a copy/store within the loop. |
| |
| Enabled by default when @option{-fgcse} is enabled. |
| |
| @item -fgcse-sm |
| @opindex fgcse-sm |
| When @option{-fgcse-sm} is enabled, a store motion pass is run after |
| global common subexpression elimination. This pass attempts to move |
| stores out of loops. When used in conjunction with @option{-fgcse-lm}, |
| loops containing a load/store sequence can be changed to a load before |
| the loop and a store after the loop. |
| |
| Not enabled at any optimization level. |
| |
| @item -fgcse-las |
| @opindex fgcse-las |
| When @option{-fgcse-las} is enabled, the global common subexpression |
| elimination pass eliminates redundant loads that come after stores to the |
| same memory location (both partial and full redundancies). |
| |
| Not enabled at any optimization level. |
| |
| @item -fgcse-after-reload |
| @opindex fgcse-after-reload |
| When @option{-fgcse-after-reload} is enabled, a redundant load elimination |
| pass is performed after reload. The purpose of this pass is to clean up |
| redundant spilling. |
| |
| @item -funsafe-loop-optimizations |
| @opindex funsafe-loop-optimizations |
| This option tells the loop optimizer to assume that loop indices do not |
| overflow, and that loops with nontrivial exit condition are not |
| infinite. This enables a wider range of loop optimizations even if |
| the loop optimizer itself cannot prove that these assumptions are valid. |
| If you use @option{-Wunsafe-loop-optimizations}, the compiler warns you |
| if it finds this kind of loop. |
| |
| @item -fcrossjumping |
| @opindex fcrossjumping |
| Perform cross-jumping transformation. |
| This transformation unifies equivalent code and saves code size. The |
| resulting code may or may not perform better than without cross-jumping. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fauto-inc-dec |
| @opindex fauto-inc-dec |
| Combine increments or decrements of addresses with memory accesses. |
| This pass is always skipped on architectures that do not have |
| instructions to support this. Enabled by default at @option{-O} and |
| higher on architectures that support this. |
| |
| @item -fdce |
| @opindex fdce |
| Perform dead code elimination (DCE) on RTL@. |
| Enabled by default at @option{-O} and higher. |
| |
| @item -fdse |
| @opindex fdse |
| Perform dead store elimination (DSE) on RTL@. |
| Enabled by default at @option{-O} and higher. |
| |
| @item -fif-conversion |
| @opindex fif-conversion |
| Attempt to transform conditional jumps into branch-less equivalents. This |
| includes use of conditional moves, min, max, set flags and abs instructions, and |
| some tricks doable by standard arithmetics. The use of conditional execution |
| on chips where it is available is controlled by @code{if-conversion2}. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fif-conversion2 |
| @opindex fif-conversion2 |
| Use conditional execution (where available) to transform conditional jumps into |
| branch-less equivalents. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fdelete-null-pointer-checks |
| @opindex fdelete-null-pointer-checks |
| Assume that programs cannot safely dereference null pointers, and that |
| no code or data element resides there. This enables simple constant |
| folding optimizations at all optimization levels. In addition, other |
| optimization passes in GCC use this flag to control global dataflow |
| analyses that eliminate useless checks for null pointers; these assume |
| that if a pointer is checked after it has already been dereferenced, |
| it cannot be null. |
| |
| Note however that in some environments this assumption is not true. |
| Use @option{-fno-delete-null-pointer-checks} to disable this optimization |
| for programs that depend on that behavior. |
| |
| Some targets, especially embedded ones, disable this option at all levels. |
| Otherwise it is enabled at all levels: @option{-O0}, @option{-O1}, |
| @option{-O2}, @option{-O3}, @option{-Os}. Passes that use the information |
| are enabled independently at different optimization levels. |
| |
| @item -fdevirtualize |
| @opindex fdevirtualize |
| Attempt to convert calls to virtual functions to direct calls. This |
| is done both within a procedure and interprocedurally as part of |
| indirect inlining (@code{-findirect-inlining}) and interprocedural constant |
| propagation (@option{-fipa-cp}). |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fexpensive-optimizations |
| @opindex fexpensive-optimizations |
| Perform a number of minor optimizations that are relatively expensive. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -free |
| @opindex free |
| Attempt to remove redundant extension instructions. This is especially |
| helpful for the x86-64 architecture, which implicitly zero-extends in 64-bit |
| registers after writing to their lower 32-bit half. |
| |
| Enabled for x86 at levels @option{-O2}, @option{-O3}. |
| |
| @item -foptimize-register-move |
| @itemx -fregmove |
| @opindex foptimize-register-move |
| @opindex fregmove |
| Attempt to reassign register numbers in move instructions and as |
| operands of other simple instructions in order to maximize the amount of |
| register tying. This is especially helpful on machines with two-operand |
| instructions. |
| |
| Note @option{-fregmove} and @option{-foptimize-register-move} are the same |
| optimization. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fira-algorithm=@var{algorithm} |
| Use the specified coloring algorithm for the integrated register |
| allocator. The @var{algorithm} argument can be @samp{priority}, which |
| specifies Chow's priority coloring, or @samp{CB}, which specifies |
| Chaitin-Briggs coloring. Chaitin-Briggs coloring is not implemented |
| for all architectures, but for those targets that do support it, it is |
| the default because it generates better code. |
| |
| @item -fira-region=@var{region} |
| Use specified regions for the integrated register allocator. The |
| @var{region} argument should be one of the following: |
| |
| @table @samp |
| |
| @item all |
| Use all loops as register allocation regions. |
| This can give the best results for machines with a small and/or |
| irregular register set. |
| |
| @item mixed |
| Use all loops except for loops with small register pressure |
| as the regions. This value usually gives |
| the best results in most cases and for most architectures, |
| and is enabled by default when compiling with optimization for speed |
| (@option{-O}, @option{-O2}, @dots{}). |
| |
| @item one |
| Use all functions as a single region. |
| This typically results in the smallest code size, and is enabled by default for |
| @option{-Os} or @option{-O0}. |
| |
| @end table |
| |
| @item -fira-loop-pressure |
| @opindex fira-loop-pressure |
| Use IRA to evaluate register pressure in loops for decisions to move |
| loop invariants. This option usually results in generation |
| of faster and smaller code on machines with large register files (>= 32 |
| registers), but it can slow the compiler down. |
| |
| This option is enabled at level @option{-O3} for some targets. |
| |
| @item -fno-ira-share-save-slots |
| @opindex fno-ira-share-save-slots |
| Disable sharing of stack slots used for saving call-used hard |
| registers living through a call. Each hard register gets a |
| separate stack slot, and as a result function stack frames are |
| larger. |
| |
| @item -fno-ira-share-spill-slots |
| @opindex fno-ira-share-spill-slots |
| Disable sharing of stack slots allocated for pseudo-registers. Each |
| pseudo-register that does not get a hard register gets a separate |
| stack slot, and as a result function stack frames are larger. |
| |
| @item -fira-verbose=@var{n} |
| @opindex fira-verbose |
| Control the verbosity of the dump file for the integrated register allocator. |
| The default value is 5. If the value @var{n} is greater or equal to 10, |
| the dump output is sent to stderr using the same format as @var{n} minus 10. |
| |
| @item -fdelayed-branch |
| @opindex fdelayed-branch |
| If supported for the target machine, attempt to reorder instructions |
| to exploit instruction slots available after delayed branch |
| instructions. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fschedule-insns |
| @opindex fschedule-insns |
| If supported for the target machine, attempt to reorder instructions to |
| eliminate execution stalls due to required data being unavailable. This |
| helps machines that have slow floating point or memory load instructions |
| by allowing other instructions to be issued until the result of the load |
| or floating-point instruction is required. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -fschedule-insns2 |
| @opindex fschedule-insns2 |
| Similar to @option{-fschedule-insns}, but requests an additional pass of |
| instruction scheduling after register allocation has been done. This is |
| especially useful on machines with a relatively small number of |
| registers and where memory load instructions take more than one cycle. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fno-sched-interblock |
| @opindex fno-sched-interblock |
| Don't schedule instructions across basic blocks. This is normally |
| enabled by default when scheduling before register allocation, i.e.@: |
| with @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fno-sched-spec |
| @opindex fno-sched-spec |
| Don't allow speculative motion of non-load instructions. This is normally |
| enabled by default when scheduling before register allocation, i.e.@: |
| with @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-pressure |
| @opindex fsched-pressure |
| Enable register pressure sensitive insn scheduling before register |
| allocation. This only makes sense when scheduling before register |
| allocation is enabled, i.e.@: with @option{-fschedule-insns} or at |
| @option{-O2} or higher. Usage of this option can improve the |
| generated code and decrease its size by preventing register pressure |
| increase above the number of available hard registers and subsequent |
| spills in register allocation. |
| |
| @item -fsched-spec-load |
| @opindex fsched-spec-load |
| Allow speculative motion of some load instructions. This only makes |
| sense when scheduling before register allocation, i.e.@: with |
| @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-spec-load-dangerous |
| @opindex fsched-spec-load-dangerous |
| Allow speculative motion of more load instructions. This only makes |
| sense when scheduling before register allocation, i.e.@: with |
| @option{-fschedule-insns} or at @option{-O2} or higher. |
| |
| @item -fsched-stalled-insns |
| @itemx -fsched-stalled-insns=@var{n} |
| @opindex fsched-stalled-insns |
| Define how many insns (if any) can be moved prematurely from the queue |
| of stalled insns into the ready list during the second scheduling pass. |
| @option{-fno-sched-stalled-insns} means that no insns are moved |
| prematurely, @option{-fsched-stalled-insns=0} means there is no limit |
| on how many queued insns can be moved prematurely. |
| @option{-fsched-stalled-insns} without a value is equivalent to |
| @option{-fsched-stalled-insns=1}. |
| |
| @item -fsched-stalled-insns-dep |
| @itemx -fsched-stalled-insns-dep=@var{n} |
| @opindex fsched-stalled-insns-dep |
| Define how many insn groups (cycles) are examined for a dependency |
| on a stalled insn that is a candidate for premature removal from the queue |
| of stalled insns. This has an effect only during the second scheduling pass, |
| and only if @option{-fsched-stalled-insns} is used. |
| @option{-fno-sched-stalled-insns-dep} is equivalent to |
| @option{-fsched-stalled-insns-dep=0}. |
| @option{-fsched-stalled-insns-dep} without a value is equivalent to |
| @option{-fsched-stalled-insns-dep=1}. |
| |
| @item -fsched2-use-superblocks |
| @opindex fsched2-use-superblocks |
| When scheduling after register allocation, use superblock scheduling. |
| This allows motion across basic block boundaries, |
| resulting in faster schedules. This option is experimental, as not all machine |
| descriptions used by GCC model the CPU closely enough to avoid unreliable |
| results from the algorithm. |
| |
| This only makes sense when scheduling after register allocation, i.e.@: with |
| @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-group-heuristic |
| @opindex fsched-group-heuristic |
| Enable the group heuristic in the scheduler. This heuristic favors |
| the instruction that belongs to a schedule group. This is enabled |
| by default when scheduling is enabled, i.e.@: with @option{-fschedule-insns} |
| or @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-critical-path-heuristic |
| @opindex fsched-critical-path-heuristic |
| Enable the critical-path heuristic in the scheduler. This heuristic favors |
| instructions on the critical path. This is enabled by default when |
| scheduling is enabled, i.e.@: with @option{-fschedule-insns} |
| or @option{-fschedule-insns2} or at @option{-O2} or higher. |
| |
| @item -fsched-spec-insn-heuristic |
| @opindex fsched-spec-insn-heuristic |
| Enable the speculative instruction heuristic in the scheduler. This |
| heuristic favors speculative instructions with greater dependency weakness. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} |
| or at @option{-O2} or higher. |
| |
| @item -fsched-rank-heuristic |
| @opindex fsched-rank-heuristic |
| Enable the rank heuristic in the scheduler. This heuristic favors |
| the instruction belonging to a basic block with greater size or frequency. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -fsched-last-insn-heuristic |
| @opindex fsched-last-insn-heuristic |
| Enable the last-instruction heuristic in the scheduler. This heuristic |
| favors the instruction that is less dependent on the last instruction |
| scheduled. This is enabled by default when scheduling is enabled, |
| i.e.@: with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -fsched-dep-count-heuristic |
| @opindex fsched-dep-count-heuristic |
| Enable the dependent-count heuristic in the scheduler. This heuristic |
| favors the instruction that has more instructions depending on it. |
| This is enabled by default when scheduling is enabled, i.e.@: |
| with @option{-fschedule-insns} or @option{-fschedule-insns2} or |
| at @option{-O2} or higher. |
| |
| @item -freschedule-modulo-scheduled-loops |
| @opindex freschedule-modulo-scheduled-loops |
| Modulo scheduling is performed before traditional scheduling. If a loop |
| is modulo scheduled, later scheduling passes may change its schedule. |
| Use this option to control that behavior. |
| |
| @item -fselective-scheduling |
| @opindex fselective-scheduling |
| Schedule instructions using selective scheduling algorithm. Selective |
| scheduling runs instead of the first scheduler pass. |
| |
| @item -fselective-scheduling2 |
| @opindex fselective-scheduling2 |
| Schedule instructions using selective scheduling algorithm. Selective |
| scheduling runs instead of the second scheduler pass. |
| |
| @item -fsel-sched-pipelining |
| @opindex fsel-sched-pipelining |
| Enable software pipelining of innermost loops during selective scheduling. |
| This option has no effect unless one of @option{-fselective-scheduling} or |
| @option{-fselective-scheduling2} is turned on. |
| |
| @item -fsel-sched-pipelining-outer-loops |
| @opindex fsel-sched-pipelining-outer-loops |
| When pipelining loops during selective scheduling, also pipeline outer loops. |
| This option has no effect unless @option{-fsel-sched-pipelining} is turned on. |
| |
| @item -fshrink-wrap |
| @opindex fshrink-wrap |
| Emit function prologues only before parts of the function that need it, |
| rather than at the top of the function. This flag is enabled by default at |
| @option{-O} and higher. |
| |
| @item -fcaller-saves |
| @opindex fcaller-saves |
| Enable allocation of values to registers that are clobbered by |
| function calls, by emitting extra instructions to save and restore the |
| registers around such calls. Such allocation is done only when it |
| seems to result in better code. |
| |
| This option is always enabled by default on certain machines, usually |
| those which have no call-preserved registers to use instead. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcombine-stack-adjustments |
| @opindex fcombine-stack-adjustments |
| Tracks stack adjustments (pushes and pops) and stack memory references |
| and then tries to find ways to combine them. |
| |
| Enabled by default at @option{-O1} and higher. |
| |
| @item -fconserve-stack |
| @opindex fconserve-stack |
| Attempt to minimize stack usage. The compiler attempts to use less |
| stack space, even if that makes the program slower. This option |
| implies setting the @option{large-stack-frame} parameter to 100 |
| and the @option{large-stack-frame-growth} parameter to 400. |
| |
| @item -ftree-reassoc |
| @opindex ftree-reassoc |
| Perform reassociation on trees. This flag is enabled by default |
| at @option{-O} and higher. |
| |
| @item -ftree-pre |
| @opindex ftree-pre |
| Perform partial redundancy elimination (PRE) on trees. This flag is |
| enabled by default at @option{-O2} and @option{-O3}. |
| |
| @item -ftree-partial-pre |
| @opindex ftree-partial-pre |
| Make partial redundancy elimination (PRE) more aggressive. This flag is |
| enabled by default at @option{-O3}. |
| |
| @item -ftree-forwprop |
| @opindex ftree-forwprop |
| Perform forward propagation on trees. This flag is enabled by default |
| at @option{-O} and higher. |
| |
| @item -ftree-fre |
| @opindex ftree-fre |
| Perform full redundancy elimination (FRE) on trees. The difference |
| between FRE and PRE is that FRE only considers expressions |
| that are computed on all paths leading to the redundant computation. |
| This analysis is faster than PRE, though it exposes fewer redundancies. |
| This flag is enabled by default at @option{-O} and higher. |
| |
| @item -ftree-phiprop |
| @opindex ftree-phiprop |
| Perform hoisting of loads from conditional pointers on trees. This |
| pass is enabled by default at @option{-O} and higher. |
| |
| @item -fhoist-adjacent-loads |
| @opindex hoist-adjacent-loads |
| Speculatively hoist loads from both branches of an if-then-else if the |
| loads are from adjacent locations in the same structure and the target |
| architecture has a conditional move instruction. This flag is enabled |
| by default at @option{-O2} and higher. |
| |
| @item -ftree-copy-prop |
| @opindex ftree-copy-prop |
| Perform copy propagation on trees. This pass eliminates unnecessary |
| copy operations. This flag is enabled by default at @option{-O} and |
| higher. |
| |
| @item -fipa-pure-const |
| @opindex fipa-pure-const |
| Discover which functions are pure or constant. |
| Enabled by default at @option{-O} and higher. |
| |
| @item -fipa-reference |
| @opindex fipa-reference |
| Discover which static variables do not escape the |
| compilation unit. |
| Enabled by default at @option{-O} and higher. |
| |
| @item -fipa-pta |
| @opindex fipa-pta |
| Perform interprocedural pointer analysis and interprocedural modification |
| and reference analysis. This option can cause excessive memory and |
| compile-time usage on large compilation units. It is not enabled by |
| default at any optimization level. |
| |
| @item -fipa-profile |
| @opindex fipa-profile |
| Perform interprocedural profile propagation. The functions called only from |
| cold functions are marked as cold. Also functions executed once (such as |
| @code{cold}, @code{noreturn}, static constructors or destructors) are identified. Cold |
| functions and loop less parts of functions executed once are then optimized for |
| size. |
| Enabled by default at @option{-O} and higher. |
| |
| @item -fipa-cp |
| @opindex fipa-cp |
| Perform interprocedural constant propagation. |
| This optimization analyzes the program to determine when values passed |
| to functions are constants and then optimizes accordingly. |
| This optimization can substantially increase performance |
| if the application has constants passed to functions. |
| This flag is enabled by default at @option{-O2}, @option{-Os} and @option{-O3}. |
| |
| @item -fipa-cp-clone |
| @opindex fipa-cp-clone |
| Perform function cloning to make interprocedural constant propagation stronger. |
| When enabled, interprocedural constant propagation performs function cloning |
| when externally visible function can be called with constant arguments. |
| Because this optimization can create multiple copies of functions, |
| it may significantly increase code size |
| (see @option{--param ipcp-unit-growth=@var{value}}). |
| This flag is enabled by default at @option{-O3}. |
| |
| @item -ftree-sink |
| @opindex ftree-sink |
| Perform forward store motion on trees. This flag is |
| enabled by default at @option{-O} and higher. |
| |
| @item -ftree-bit-ccp |
| @opindex ftree-bit-ccp |
| Perform sparse conditional bit constant propagation on trees and propagate |
| pointer alignment information. |
| This pass only operates on local scalar variables and is enabled by default |
| at @option{-O} and higher. It requires that @option{-ftree-ccp} is enabled. |
| |
| @item -ftree-ccp |
| @opindex ftree-ccp |
| Perform sparse conditional constant propagation (CCP) on trees. This |
| pass only operates on local scalar variables and is enabled by default |
| at @option{-O} and higher. |
| |
| @item -ftree-switch-conversion |
| Perform conversion of simple initializations in a switch to |
| initializations from a scalar array. This flag is enabled by default |
| at @option{-O2} and higher. |
| |
| @item -ftree-tail-merge |
| Look for identical code sequences. When found, replace one with a jump to the |
| other. This optimization is known as tail merging or cross jumping. This flag |
| is enabled by default at @option{-O2} and higher. The compilation time |
| in this pass can |
| be limited using @option{max-tail-merge-comparisons} parameter and |
| @option{max-tail-merge-iterations} parameter. |
| |
| @item -ftree-dce |
| @opindex ftree-dce |
| Perform dead code elimination (DCE) on trees. This flag is enabled by |
| default at @option{-O} and higher. |
| |
| @item -ftree-builtin-call-dce |
| @opindex ftree-builtin-call-dce |
| Perform conditional dead code elimination (DCE) for calls to built-in functions |
| that may set @code{errno} but are otherwise side-effect free. This flag is |
| enabled by default at @option{-O2} and higher if @option{-Os} is not also |
| specified. |
| |
| @item -ftree-dominator-opts |
| @opindex ftree-dominator-opts |
| Perform a variety of simple scalar cleanups (constant/copy |
| propagation, redundancy elimination, range propagation and expression |
| simplification) based on a dominator tree traversal. This also |
| performs jump threading (to reduce jumps to jumps). This flag is |
| enabled by default at @option{-O} and higher. |
| |
| @item -ftree-dse |
| @opindex ftree-dse |
| Perform dead store elimination (DSE) on trees. A dead store is a store into |
| a memory location that is later overwritten by another store without |
| any intervening loads. In this case the earlier store can be deleted. This |
| flag is enabled by default at @option{-O} and higher. |
| |
| @item -ftree-ch |
| @opindex ftree-ch |
| Perform loop header copying on trees. This is beneficial since it increases |
| effectiveness of code motion optimizations. It also saves one jump. This flag |
| is enabled by default at @option{-O} and higher. It is not enabled |
| for @option{-Os}, since it usually increases code size. |
| |
| @item -ftree-loop-optimize |
| @opindex ftree-loop-optimize |
| Perform loop optimizations on trees. This flag is enabled by default |
| at @option{-O} and higher. |
| |
| @item -ftree-loop-linear |
| @opindex ftree-loop-linear |
| Perform loop interchange transformations on tree. Same as |
| @option{-floop-interchange}. To use this code transformation, GCC has |
| to be configured with @option{--with-ppl} and @option{--with-cloog} to |
| enable the Graphite loop transformation infrastructure. |
| |
| @item -floop-interchange |
| @opindex floop-interchange |
| Perform loop interchange transformations on loops. Interchanging two |
| nested loops switches the inner and outer loops. For example, given a |
| loop like: |
| @smallexample |
| DO J = 1, M |
| DO I = 1, N |
| A(J, I) = A(J, I) * C |
| ENDDO |
| ENDDO |
| @end smallexample |
| loop interchange transforms the loop as if it were written: |
| @smallexample |
| DO I = 1, N |
| DO J = 1, M |
| A(J, I) = A(J, I) * C |
| ENDDO |
| ENDDO |
| @end smallexample |
| which can be beneficial when @code{N} is larger than the caches, |
| because in Fortran, the elements of an array are stored in memory |
| contiguously by column, and the original loop iterates over rows, |
| potentially creating at each access a cache miss. This optimization |
| applies to all the languages supported by GCC and is not limited to |
| Fortran. To use this code transformation, GCC has to be configured |
| with @option{--with-ppl} and @option{--with-cloog} to enable the |
| Graphite loop transformation infrastructure. |
| |
| @item -floop-strip-mine |
| @opindex floop-strip-mine |
| Perform loop strip mining transformations on loops. Strip mining |
| splits a loop into two nested loops. The outer loop has strides |
| equal to the strip size and the inner loop has strides of the |
| original loop within a strip. The strip length can be changed |
| using the @option{loop-block-tile-size} parameter. For example, |
| given a loop like: |
| @smallexample |
| DO I = 1, N |
| A(I) = A(I) + C |
| ENDDO |
| @end smallexample |
| loop strip mining transforms the loop as if it were written: |
| @smallexample |
| DO II = 1, N, 51 |
| DO I = II, min (II + 50, N) |
| A(I) = A(I) + C |
| ENDDO |
| ENDDO |
| @end smallexample |
| This optimization applies to all the languages supported by GCC and is |
| not limited to Fortran. To use this code transformation, GCC has to |
| be configured with @option{--with-ppl} and @option{--with-cloog} to |
| enable the Graphite loop transformation infrastructure. |
| |
| @item -floop-block |
| @opindex floop-block |
| Perform loop blocking transformations on loops. Blocking strip mines |
| each loop in the loop nest such that the memory accesses of the |
| element loops fit inside caches. The strip length can be changed |
| using the @option{loop-block-tile-size} parameter. For example, given |
| a loop like: |
| @smallexample |
| DO I = 1, N |
| DO J = 1, M |
| A(J, I) = B(I) + C(J) |
| ENDDO |
| ENDDO |
| @end smallexample |
| loop blocking transforms the loop as if it were written: |
| @smallexample |
| DO II = 1, N, 51 |
| DO JJ = 1, M, 51 |
| DO I = II, min (II + 50, N) |
| DO J = JJ, min (JJ + 50, M) |
| A(J, I) = B(I) + C(J) |
| ENDDO |
| ENDDO |
| ENDDO |
| ENDDO |
| @end smallexample |
| which can be beneficial when @code{M} is larger than the caches, |
| because the innermost loop iterates over a smaller amount of data |
| which can be kept in the caches. This optimization applies to all the |
| languages supported by GCC and is not limited to Fortran. To use this |
| code transformation, GCC has to be configured with @option{--with-ppl} |
| and @option{--with-cloog} to enable the Graphite loop transformation |
| infrastructure. |
| |
| @item -fgraphite-identity |
| @opindex fgraphite-identity |
| Enable the identity transformation for graphite. For every SCoP we generate |
| the polyhedral representation and transform it back to gimple. Using |
| @option{-fgraphite-identity} we can check the costs or benefits of the |
| GIMPLE -> GRAPHITE -> GIMPLE transformation. Some minimal optimizations |
| are also performed by the code generator CLooG, like index splitting and |
| dead code elimination in loops. |
| |
| @item -floop-nest-optimize |
| @opindex floop-nest-optimize |
| Enable the ISL based loop nest optimizer. This is a generic loop nest |
| optimizer based on the Pluto optimization algorithms. It calculates a loop |
| structure optimized for data-locality and parallelism. This option |
| is experimental. |
| |
| @item -floop-parallelize-all |
| @opindex floop-parallelize-all |
| Use the Graphite data dependence analysis to identify loops that can |
| be parallelized. Parallelize all the loops that can be analyzed to |
| not contain loop carried dependences without checking that it is |
| profitable to parallelize the loops. |
| |
| @item -fcheck-data-deps |
| @opindex fcheck-data-deps |
| Compare the results of several data dependence analyzers. This option |
| is used for debugging the data dependence analyzers. |
| |
| @item -ftree-loop-if-convert |
| Attempt to transform conditional jumps in the innermost loops to |
| branch-less equivalents. The intent is to remove control-flow from |
| the innermost loops in order to improve the ability of the |
| vectorization pass to handle these loops. This is enabled by default |
| if vectorization is enabled. |
| |
| @item -ftree-loop-if-convert-stores |
| Attempt to also if-convert conditional jumps containing memory writes. |
| This transformation can be unsafe for multi-threaded programs as it |
| transforms conditional memory writes into unconditional memory writes. |
| For example, |
| @smallexample |
| for (i = 0; i < N; i++) |
| if (cond) |
| A[i] = expr; |
| @end smallexample |
| is transformed to |
| @smallexample |
| for (i = 0; i < N; i++) |
| A[i] = cond ? expr : A[i]; |
| @end smallexample |
| potentially producing data races. |
| |
| @item -ftree-loop-distribution |
| Perform loop distribution. This flag can improve cache performance on |
| big loop bodies and allow further loop optimizations, like |
| parallelization or vectorization, to take place. For example, the loop |
| @smallexample |
| DO I = 1, N |
| A(I) = B(I) + C |
| D(I) = E(I) * F |
| ENDDO |
| @end smallexample |
| is transformed to |
| @smallexample |
| DO I = 1, N |
| A(I) = B(I) + C |
| ENDDO |
| DO I = 1, N |
| D(I) = E(I) * F |
| ENDDO |
| @end smallexample |
| |
| @item -ftree-loop-distribute-patterns |
| Perform loop distribution of patterns that can be code generated with |
| calls to a library. This flag is enabled by default at @option{-O3}. |
| |
| This pass distributes the initialization loops and generates a call to |
| memset zero. For example, the loop |
| @smallexample |
| DO I = 1, N |
| A(I) = 0 |
| B(I) = A(I) + I |
| ENDDO |
| @end smallexample |
| is transformed to |
| @smallexample |
| DO I = 1, N |
| A(I) = 0 |
| ENDDO |
| DO I = 1, N |
| B(I) = A(I) + I |
| ENDDO |
| @end smallexample |
| and the initialization loop is transformed into a call to memset zero. |
| |
| @item -ftree-loop-im |
| @opindex ftree-loop-im |
| Perform loop invariant motion on trees. This pass moves only invariants that |
| are hard to handle at RTL level (function calls, operations that expand to |
| nontrivial sequences of insns). With @option{-funswitch-loops} it also moves |
| operands of conditions that are invariant out of the loop, so that we can use |
| just trivial invariantness analysis in loop unswitching. The pass also includes |
| store motion. |
| |
| @item -ftree-loop-ivcanon |
| @opindex ftree-loop-ivcanon |
| Create a canonical counter for number of iterations in loops for which |
| determining number of iterations requires complicated analysis. Later |
| optimizations then may determine the number easily. Useful especially |
| in connection with unrolling. |
| |
| @item -fivopts |
| @opindex fivopts |
| Perform induction variable optimizations (strength reduction, induction |
| variable merging and induction variable elimination) on trees. |
| |
| @item -ftree-parallelize-loops=n |
| @opindex ftree-parallelize-loops |
| Parallelize loops, i.e., split their iteration space to run in n threads. |
| This is only possible for loops whose iterations are independent |
| and can be arbitrarily reordered. The optimization is only |
| profitable on multiprocessor machines, for loops that are CPU-intensive, |
| rather than constrained e.g.@: by memory bandwidth. This option |
| implies @option{-pthread}, and thus is only supported on targets |
| that have support for @option{-pthread}. |
| |
| @item -ftree-pta |
| @opindex ftree-pta |
| Perform function-local points-to analysis on trees. This flag is |
| enabled by default at @option{-O} and higher. |
| |
| @item -ftree-sra |
| @opindex ftree-sra |
| Perform scalar replacement of aggregates. This pass replaces structure |
| references with scalars to prevent committing structures to memory too |
| early. This flag is enabled by default at @option{-O} and higher. |
| |
| @item -ftree-copyrename |
| @opindex ftree-copyrename |
| Perform copy renaming on trees. This pass attempts to rename compiler |
| temporaries to other variables at copy locations, usually resulting in |
| variable names which more closely resemble the original variables. This flag |
| is enabled by default at @option{-O} and higher. |
| |
| @item -ftree-coalesce-inlined-vars |
| Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to |
| combine small user-defined variables too, but only if they were inlined |
| from other functions. It is a more limited form of |
| @option{-ftree-coalesce-vars}. This may harm debug information of such |
| inlined variables, but it will keep variables of the inlined-into |
| function apart from each other, such that they are more likely to |
| contain the expected values in a debugging session. This was the |
| default in GCC versions older than 4.7. |
| |
| @item -ftree-coalesce-vars |
| Tell the copyrename pass (see @option{-ftree-copyrename}) to attempt to |
| combine small user-defined variables too, instead of just compiler |
| temporaries. This may severely limit the ability to debug an optimized |
| program compiled with @option{-fno-var-tracking-assignments}. In the |
| negated form, this flag prevents SSA coalescing of user variables, |
| including inlined ones. This option is enabled by default. |
| |
| @item -ftree-ter |
| @opindex ftree-ter |
| Perform temporary expression replacement during the SSA->normal phase. Single |
| use/single def temporaries are replaced at their use location with their |
| defining expression. This results in non-GIMPLE code, but gives the expanders |
| much more complex trees to work on resulting in better RTL generation. This is |
| enabled by default at @option{-O} and higher. |
| |
| @item -ftree-slsr |
| @opindex ftree-slsr |
| Perform straight-line strength reduction on trees. This recognizes related |
| expressions involving multiplications and replaces them by less expensive |
| calculations when possible. This is enabled by default at @option{-O} and |
| higher. |
| |
| @item -ftree-vectorize |
| @opindex ftree-vectorize |
| Perform loop vectorization on trees. This flag is enabled by default at |
| @option{-O3}. |
| |
| @item -ftree-slp-vectorize |
| @opindex ftree-slp-vectorize |
| Perform basic block vectorization on trees. This flag is enabled by default at |
| @option{-O3} and when @option{-ftree-vectorize} is enabled. |
| |
| @item -ftree-vect-loop-version |
| @opindex ftree-vect-loop-version |
| Perform loop versioning when doing loop vectorization on trees. When a loop |
| appears to be vectorizable except that data alignment or data dependence cannot |
| be determined at compile time, then vectorized and non-vectorized versions of |
| the loop are generated along with run-time checks for alignment or dependence |
| to control which version is executed. This option is enabled by default |
| except at level @option{-Os} where it is disabled. |
| |
| @item -fvect-cost-model |
| @opindex fvect-cost-model |
| Enable cost model for vectorization. This option is enabled by default at |
| @option{-O3}. |
| |
| @item -ftree-vrp |
| @opindex ftree-vrp |
| Perform Value Range Propagation on trees. This is similar to the |
| constant propagation pass, but instead of values, ranges of values are |
| propagated. This allows the optimizers to remove unnecessary range |
| checks like array bound checks and null pointer checks. This is |
| enabled by default at @option{-O2} and higher. Null pointer check |
| elimination is only done if @option{-fdelete-null-pointer-checks} is |
| enabled. |
| |
| @item -ftracer |
| @opindex ftracer |
| Perform tail duplication to enlarge superblock size. This transformation |
| simplifies the control flow of the function allowing other optimizations to do |
| a better job. |
| |
| @item -funroll-loops |
| @opindex funroll-loops |
| Unroll loops whose number of iterations can be determined at compile |
| time or upon entry to the loop. @option{-funroll-loops} implies |
| @option{-frerun-cse-after-loop}. This option makes code larger, |
| and may or may not make it run faster. |
| |
| @item -funroll-all-loops |
| @opindex funroll-all-loops |
| Unroll all loops, even if their number of iterations is uncertain when |
| the loop is entered. This usually makes programs run more slowly. |
| @option{-funroll-all-loops} implies the same options as |
| @option{-funroll-loops}, |
| |
| @item -fsplit-ivs-in-unroller |
| @opindex fsplit-ivs-in-unroller |
| Enables expression of values of induction variables in later iterations |
| of the unrolled loop using the value in the first iteration. This breaks |
| long dependency chains, thus improving efficiency of the scheduling passes. |
| |
| A combination of @option{-fweb} and CSE is often sufficient to obtain the |
| same effect. However, that is not reliable in cases where the loop body |
| is more complicated than a single basic block. It also does not work at all |
| on some architectures due to restrictions in the CSE pass. |
| |
| This optimization is enabled by default. |
| |
| @item -fvariable-expansion-in-unroller |
| @opindex fvariable-expansion-in-unroller |
| With this option, the compiler creates multiple copies of some |
| local variables when unrolling a loop, which can result in superior code. |
| |
| @item -fpartial-inlining |
| @opindex fpartial-inlining |
| Inline parts of functions. This option has any effect only |
| when inlining itself is turned on by the @option{-finline-functions} |
| or @option{-finline-small-functions} options. |
| |
| Enabled at level @option{-O2}. |
| |
| @item -fpredictive-commoning |
| @opindex fpredictive-commoning |
| Perform predictive commoning optimization, i.e., reusing computations |
| (especially memory loads and stores) performed in previous |
| iterations of loops. |
| |
| This option is enabled at level @option{-O3}. |
| |
| @item -fprefetch-loop-arrays |
| @opindex fprefetch-loop-arrays |
| If supported by the target machine, generate instructions to prefetch |
| memory to improve the performance of loops that access large arrays. |
| |
| This option may generate better or worse code; results are highly |
| dependent on the structure of loops within the source code. |
| |
| Disabled at level @option{-Os}. |
| |
| @item -fno-peephole |
| @itemx -fno-peephole2 |
| @opindex fno-peephole |
| @opindex fno-peephole2 |
| Disable any machine-specific peephole optimizations. The difference |
| between @option{-fno-peephole} and @option{-fno-peephole2} is in how they |
| are implemented in the compiler; some targets use one, some use the |
| other, a few use both. |
| |
| @option{-fpeephole} is enabled by default. |
| @option{-fpeephole2} enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fno-guess-branch-probability |
| @opindex fno-guess-branch-probability |
| Do not guess branch probabilities using heuristics. |
| |
| GCC uses heuristics to guess branch probabilities if they are |
| not provided by profiling feedback (@option{-fprofile-arcs}). These |
| heuristics are based on the control flow graph. If some branch probabilities |
| are specified by @samp{__builtin_expect}, then the heuristics are |
| used to guess branch probabilities for the rest of the control flow graph, |
| taking the @samp{__builtin_expect} info into account. The interactions |
| between the heuristics and @samp{__builtin_expect} can be complex, and in |
| some cases, it may be useful to disable the heuristics so that the effects |
| of @samp{__builtin_expect} are easier to understand. |
| |
| The default is @option{-fguess-branch-probability} at levels |
| @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -freorder-blocks |
| @opindex freorder-blocks |
| Reorder basic blocks in the compiled function in order to reduce number of |
| taken branches and improve code locality. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -freorder-blocks-and-partition |
| @opindex freorder-blocks-and-partition |
| In addition to reordering basic blocks in the compiled function, in order |
| to reduce number of taken branches, partitions hot and cold basic blocks |
| into separate sections of the assembly and .o files, to improve |
| paging and cache locality performance. |
| |
| This optimization is automatically turned off in the presence of |
| exception handling, for linkonce sections, for functions with a user-defined |
| section attribute and on any architecture that does not support named |
| sections. |
| |
| @item -freorder-functions |
| @opindex freorder-functions |
| Reorder functions in the object file in order to |
| improve code locality. This is implemented by using special |
| subsections @code{.text.hot} for most frequently executed functions and |
| @code{.text.unlikely} for unlikely executed functions. Reordering is done by |
| the linker so object file format must support named sections and linker must |
| place them in a reasonable way. |
| |
| Also profile feedback must be available to make this option effective. See |
| @option{-fprofile-arcs} for details. |
| |
| Enabled at levels @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fstrict-aliasing |
| @opindex fstrict-aliasing |
| Allow the compiler to assume the strictest aliasing rules applicable to |
| the language being compiled. For C (and C++), this activates |
| optimizations based on the type of expressions. In particular, an |
| object of one type is assumed never to reside at the same address as an |
| object of a different type, unless the types are almost the same. For |
| example, an @code{unsigned int} can alias an @code{int}, but not a |
| @code{void*} or a @code{double}. A character type may alias any other |
| type. |
| |
| @anchor{Type-punning}Pay special attention to code like this: |
| @smallexample |
| union a_union @{ |
| int i; |
| double d; |
| @}; |
| |
| int f() @{ |
| union a_union t; |
| t.d = 3.0; |
| return t.i; |
| @} |
| @end smallexample |
| The practice of reading from a different union member than the one most |
| recently written to (called ``type-punning'') is common. Even with |
| @option{-fstrict-aliasing}, type-punning is allowed, provided the memory |
| is accessed through the union type. So, the code above works as |
| expected. @xref{Structures unions enumerations and bit-fields |
| implementation}. However, this code might not: |
| @smallexample |
| int f() @{ |
| union a_union t; |
| int* ip; |
| t.d = 3.0; |
| ip = &t.i; |
| return *ip; |
| @} |
| @end smallexample |
| |
| Similarly, access by taking the address, casting the resulting pointer |
| and dereferencing the result has undefined behavior, even if the cast |
| uses a union type, e.g.: |
| @smallexample |
| int f() @{ |
| double d = 3.0; |
| return ((union a_union *) &d)->i; |
| @} |
| @end smallexample |
| |
| The @option{-fstrict-aliasing} option is enabled at levels |
| @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fstrict-overflow |
| @opindex fstrict-overflow |
| Allow the compiler to assume strict signed overflow rules, depending |
| on the language being compiled. For C (and C++) this means that |
| overflow when doing arithmetic with signed numbers is undefined, which |
| means that the compiler may assume that it does not happen. This |
| permits various optimizations. For example, the compiler assumes |
| that an expression like @code{i + 10 > i} is always true for |
| signed @code{i}. This assumption is only valid if signed overflow is |
| undefined, as the expression is false if @code{i + 10} overflows when |
| using twos complement arithmetic. When this option is in effect any |
| attempt to determine whether an operation on signed numbers |
| overflows must be written carefully to not actually involve overflow. |
| |
| This option also allows the compiler to assume strict pointer |
| semantics: given a pointer to an object, if adding an offset to that |
| pointer does not produce a pointer to the same object, the addition is |
| undefined. This permits the compiler to conclude that @code{p + u > |
| p} is always true for a pointer @code{p} and unsigned integer |
| @code{u}. This assumption is only valid because pointer wraparound is |
| undefined, as the expression is false if @code{p + u} overflows using |
| twos complement arithmetic. |
| |
| See also the @option{-fwrapv} option. Using @option{-fwrapv} means |
| that integer signed overflow is fully defined: it wraps. When |
| @option{-fwrapv} is used, there is no difference between |
| @option{-fstrict-overflow} and @option{-fno-strict-overflow} for |
| integers. With @option{-fwrapv} certain types of overflow are |
| permitted. For example, if the compiler gets an overflow when doing |
| arithmetic on constants, the overflowed value can still be used with |
| @option{-fwrapv}, but not otherwise. |
| |
| The @option{-fstrict-overflow} option is enabled at levels |
| @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -falign-functions |
| @itemx -falign-functions=@var{n} |
| @opindex falign-functions |
| Align the start of functions to the next power-of-two greater than |
| @var{n}, skipping up to @var{n} bytes. For instance, |
| @option{-falign-functions=32} aligns functions to the next 32-byte |
| boundary, but @option{-falign-functions=24} aligns to the next |
| 32-byte boundary only if this can be done by skipping 23 bytes or less. |
| |
| @option{-fno-align-functions} and @option{-falign-functions=1} are |
| equivalent and mean that functions are not aligned. |
| |
| Some assemblers only support this flag when @var{n} is a power of two; |
| in that case, it is rounded up. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -falign-labels |
| @itemx -falign-labels=@var{n} |
| @opindex falign-labels |
| Align all branch targets to a power-of-two boundary, skipping up to |
| @var{n} bytes like @option{-falign-functions}. This option can easily |
| make code slower, because it must insert dummy operations for when the |
| branch target is reached in the usual flow of the code. |
| |
| @option{-fno-align-labels} and @option{-falign-labels=1} are |
| equivalent and mean that labels are not aligned. |
| |
| If @option{-falign-loops} or @option{-falign-jumps} are applicable and |
| are greater than this value, then their values are used instead. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default |
| which is very likely to be @samp{1}, meaning no alignment. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -falign-loops |
| @itemx -falign-loops=@var{n} |
| @opindex falign-loops |
| Align loops to a power-of-two boundary, skipping up to @var{n} bytes |
| like @option{-falign-functions}. If the loops are |
| executed many times, this makes up for any execution of the dummy |
| operations. |
| |
| @option{-fno-align-loops} and @option{-falign-loops=1} are |
| equivalent and mean that loops are not aligned. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -falign-jumps |
| @itemx -falign-jumps=@var{n} |
| @opindex falign-jumps |
| Align branch targets to a power-of-two boundary, for branch targets |
| where the targets can only be reached by jumping, skipping up to @var{n} |
| bytes like @option{-falign-functions}. In this case, no dummy operations |
| need be executed. |
| |
| @option{-fno-align-jumps} and @option{-falign-jumps=1} are |
| equivalent and mean that loops are not aligned. |
| |
| If @var{n} is not specified or is zero, use a machine-dependent default. |
| |
| Enabled at levels @option{-O2}, @option{-O3}. |
| |
| @item -funit-at-a-time |
| @opindex funit-at-a-time |
| This option is left for compatibility reasons. @option{-funit-at-a-time} |
| has no effect, while @option{-fno-unit-at-a-time} implies |
| @option{-fno-toplevel-reorder} and @option{-fno-section-anchors}. |
| |
| Enabled by default. |
| |
| @item -fno-toplevel-reorder |
| @opindex fno-toplevel-reorder |
| Do not reorder top-level functions, variables, and @code{asm} |
| statements. Output them in the same order that they appear in the |
| input file. When this option is used, unreferenced static variables |
| are not removed. This option is intended to support existing code |
| that relies on a particular ordering. For new code, it is better to |
| use attributes. |
| |
| Enabled at level @option{-O0}. When disabled explicitly, it also implies |
| @option{-fno-section-anchors}, which is otherwise enabled at @option{-O0} on some |
| targets. |
| |
| @item -fweb |
| @opindex fweb |
| Constructs webs as commonly used for register allocation purposes and assign |
| each web individual pseudo register. This allows the register allocation pass |
| to operate on pseudos directly, but also strengthens several other optimization |
| passes, such as CSE, loop optimizer and trivial dead code remover. It can, |
| however, make debugging impossible, since variables no longer stay in a |
| ``home register''. |
| |
| Enabled by default with @option{-funroll-loops}. |
| |
| @item -fwhole-program |
| @opindex fwhole-program |
| Assume that the current compilation unit represents the whole program being |
| compiled. All public functions and variables with the exception of @code{main} |
| and those merged by attribute @code{externally_visible} become static functions |
| and in effect are optimized more aggressively by interprocedural optimizers. If @command{gold} is used as the linker plugin, @code{externally_visible} attributes are automatically added to functions (not variable yet due to a current @command{gold} issue) that are accessed outside of LTO objects according to resolution file produced by @command{gold}. For other linkers that cannot generate resolution file, explicit @code{externally_visible} attributes are still necessary. |
| While this option is equivalent to proper use of the @code{static} keyword for |
| programs consisting of a single file, in combination with option |
| @option{-flto} this flag can be used to |
| compile many smaller scale programs since the functions and variables become |
| local for the whole combined compilation unit, not for the single source file |
| itself. |
| |
| This option implies @option{-fwhole-file} for Fortran programs. |
| |
| @item -flto[=@var{n}] |
| @opindex flto |
| This option runs the standard link-time optimizer. When invoked |
| with source code, it generates GIMPLE (one of GCC's internal |
| representations) and writes it to special ELF sections in the object |
| file. When the object files are linked together, all the function |
| bodies are read from these ELF sections and instantiated as if they |
| had been part of the same translation unit. |
| |
| To use the link-time optimizer, @option{-flto} needs to be specified at |
| compile time and during the final link. For example: |
| |
| @smallexample |
| gcc -c -O2 -flto foo.c |
| gcc -c -O2 -flto bar.c |
| gcc -o myprog -flto -O2 foo.o bar.o |
| @end smallexample |
| |
| The first two invocations to GCC save a bytecode representation |
| of GIMPLE into special ELF sections inside @file{foo.o} and |
| @file{bar.o}. The final invocation reads the GIMPLE bytecode from |
| @file{foo.o} and @file{bar.o}, merges the two files into a single |
| internal image, and compiles the result as usual. Since both |
| @file{foo.o} and @file{bar.o} are merged into a single image, this |
| causes all the interprocedural analyses and optimizations in GCC to |
| work across the two files as if they were a single one. This means, |
| for example, that the inliner is able to inline functions in |
| @file{bar.o} into functions in @file{foo.o} and vice-versa. |
| |
| Another (simpler) way to enable link-time optimization is: |
| |
| @smallexample |
| gcc -o myprog -flto -O2 foo.c bar.c |
| @end smallexample |
| |
| The above generates bytecode for @file{foo.c} and @file{bar.c}, |
| merges them together into a single GIMPLE representation and optimizes |
| them as usual to produce @file{myprog}. |
| |
| The only important thing to keep in mind is that to enable link-time |
| optimizations the @option{-flto} flag needs to be passed to both the |
| compile and the link commands. |
| |
| To make whole program optimization effective, it is necessary to make |
| certain whole program assumptions. The compiler needs to know |
| what functions and variables can be accessed by libraries and runtime |
| outside of the link-time optimized unit. When supported by the linker, |
| the linker plugin (see @option{-fuse-linker-plugin}) passes information |
| to the compiler about used and externally visible symbols. When |
| the linker plugin is not available, @option{-fwhole-program} should be |
| used to allow the compiler to make these assumptions, which leads |
| to more aggressive optimization decisions. |
| |
| Note that when a file is compiled with @option{-flto}, the generated |
| object file is larger than a regular object file because it |
| contains GIMPLE bytecodes and the usual final code. This means that |
| object files with LTO information can be linked as normal object |
| files; if @option{-flto} is not passed to the linker, no |
| interprocedural optimizations are applied. |
| |
| Additionally, the optimization flags used to compile individual files |
| are not necessarily related to those used at link time. For instance, |
| |
| @smallexample |
| gcc -c -O0 -flto foo.c |
| gcc -c -O0 -flto bar.c |
| gcc -o myprog -flto -O3 foo.o bar.o |
| @end smallexample |
| |
| This produces individual object files with unoptimized assembler |
| code, but the resulting binary @file{myprog} is optimized at |
| @option{-O3}. If, instead, the final binary is generated without |
| @option{-flto}, then @file{myprog} is not optimized. |
| |
| When producing the final binary with @option{-flto}, GCC only |
| applies link-time optimizations to those files that contain bytecode. |
| Therefore, you can mix and match object files and libraries with |
| GIMPLE bytecodes and final object code. GCC automatically selects |
| which files to optimize in LTO mode and which files to link without |
| further processing. |
| |
| There are some code generation flags preserved by GCC when |
| generating bytecodes, as they need to be used during the final link |
| stage. Currently, the following options are saved into the GIMPLE |
| bytecode files: @option{-fPIC}, @option{-fcommon} and all the |
| @option{-m} target flags. |
| |
| At link time, these options are read in and reapplied. Note that the |
| current implementation makes no attempt to recognize conflicting |
| values for these options. If different files have conflicting option |
| values (e.g., one file is compiled with @option{-fPIC} and another |
| isn't), the compiler simply uses the last value read from the |
| bytecode files. It is recommended, then, that you compile all the files |
| participating in the same link with the same options. |
| |
| If LTO encounters objects with C linkage declared with incompatible |
| types in separate translation units to be linked together (undefined |
| behavior according to ISO C99 6.2.7), a non-fatal diagnostic may be |
| issued. The behavior is still undefined at run time. |
| |
| Another feature of LTO is that it is possible to apply interprocedural |
| optimizations on files written in different languages. This requires |
| support in the language front end. Currently, the C, C++ and |
| Fortran front ends are capable of emitting GIMPLE bytecodes, so |
| something like this should work: |
| |
| @smallexample |
| gcc -c -flto foo.c |
| g++ -c -flto bar.cc |
| gfortran -c -flto baz.f90 |
| g++ -o myprog -flto -O3 foo.o bar.o baz.o -lgfortran |
| @end smallexample |
| |
| Notice that the final link is done with @command{g++} to get the C++ |
| runtime libraries and @option{-lgfortran} is added to get the Fortran |
| runtime libraries. In general, when mixing languages in LTO mode, you |
| should use the same link command options as when mixing languages in a |
| regular (non-LTO) compilation; all you need to add is @option{-flto} to |
| all the compile and link commands. |
| |
| If object files containing GIMPLE bytecode are stored in a library archive, say |
| @file{libfoo.a}, it is possible to extract and use them in an LTO link if you |
| are using a linker with plugin support. To enable this feature, use |
| the flag @option{-fuse-linker-plugin} at link time: |
| |
| @smallexample |
| gcc -o myprog -O2 -flto -fuse-linker-plugin a.o b.o -lfoo |
| @end smallexample |
| |
| With the linker plugin enabled, the linker extracts the needed |
| GIMPLE files from @file{libfoo.a} and passes them on to the running GCC |
| to make them part of the aggregated GIMPLE image to be optimized. |
| |
| If you are not using a linker with plugin support and/or do not |
| enable the linker plugin, then the objects inside @file{libfoo.a} |
| are extracted and linked as usual, but they do not participate |
| in the LTO optimization process. |
| |
| Link-time optimizations do not require the presence of the whole program to |
| operate. If the program does not require any symbols to be exported, it is |
| possible to combine @option{-flto} and @option{-fwhole-program} to allow |
| the interprocedural optimizers to use more aggressive assumptions which may |
| lead to improved optimization opportunities. |
| Use of @option{-fwhole-program} is not needed when linker plugin is |
| active (see @option{-fuse-linker-plugin}). |
| |
| The current implementation of LTO makes no |
| attempt to generate bytecode that is portable between different |
| types of hosts. The bytecode files are versioned and there is a |
| strict version check, so bytecode files generated in one version of |
| GCC will not work with an older/newer version of GCC@. |
| |
| Link-time optimization does not work well with generation of debugging |
| information. Combining @option{-flto} with |
| @option{-g} is currently experimental and expected to produce wrong |
| results. |
| |
| If you specify the optional @var{n}, the optimization and code |
| generation done at link time is executed in parallel using @var{n} |
| parallel jobs by utilizing an installed @command{make} program. The |
| environment variable @env{MAKE} may be used to override the program |
| used. The default value for @var{n} is 1. |
| |
| You can also specify @option{-flto=jobserver} to use GNU make's |
| job server mode to determine the number of parallel jobs. This |
| is useful when the Makefile calling GCC is already executing in parallel. |
| You must prepend a @samp{+} to the command recipe in the parent Makefile |
| for this to work. This option likely only works if @env{MAKE} is |
| GNU make. |
| |
| This option is disabled by default. |
| |
| @item -flto-partition=@var{alg} |
| @opindex flto-partition |
| Specify the partitioning algorithm used by the link-time optimizer. |
| The value is either @code{1to1} to specify a partitioning mirroring |
| the original source files or @code{balanced} to specify partitioning |
| into equally sized chunks (whenever possible) or @code{max} to create |
| new partition for every symbol where possible. Specifying @code{none} |
| as an algorithm disables partitioning and streaming completely. |
| The default value is @code{balanced}. While @code{1to1} can be used |
| as an workaround for various code ordering issues, the @code{max} |
| partitioning is intended for internal testing only. |
| |
| @item -flto-compression-level=@var{n} |
| This option specifies the level of compression used for intermediate |
| language written to LTO object files, and is only meaningful in |
| conjunction with LTO mode (@option{-flto}). Valid |
| values are 0 (no compression) to 9 (maximum compression). Values |
| outside this range are clamped to either 0 or 9. If the option is not |
| given, a default balanced compression setting is used. |
| |
| @item -flto-report |
| Prints a report with internal details on the workings of the link-time |
| optimizer. The contents of this report vary from version to version. |
| It is meant to be useful to GCC developers when processing object |
| files in LTO mode (via @option{-flto}). |
| |
| Disabled by default. |
| |
| @item -fuse-linker-plugin |
| Enables the use of a linker plugin during link-time optimization. This |
| option relies on plugin support in the linker, which is available in gold |
| or in GNU ld 2.21 or newer. |
| |
| This option enables the extraction of object files with GIMPLE bytecode out |
| of library archives. This improves the quality of optimization by exposing |
| more code to the link-time optimizer. This information specifies what |
| symbols can be accessed externally (by non-LTO object or during dynamic |
| linking). Resulting code quality improvements on binaries (and shared |
| libraries that use hidden visibility) are similar to @code{-fwhole-program}. |
| See @option{-flto} for a description of the effect of this flag and how to |
| use it. |
| |
| This option is enabled by default when LTO support in GCC is enabled |
| and GCC was configured for use with |
| a linker supporting plugins (GNU ld 2.21 or newer or gold). |
| |
| @item -ffat-lto-objects |
| @opindex ffat-lto-objects |
| Fat LTO objects are object files that contain both the intermediate language |
| and the object code. This makes them usable for both LTO linking and normal |
| linking. This option is effective only when compiling with @option{-flto} |
| and is ignored at link time. |
| |
| @option{-fno-fat-lto-objects} improves compilation time over plain LTO, but |
| requires the complete toolchain to be aware of LTO. It requires a linker with |
| linker plugin support for basic functionality. Additionally, |
| @command{nm}, @command{ar} and @command{ranlib} |
| need to support linker plugins to allow a full-featured build environment |
| (capable of building static libraries etc). gcc provides the @command{gcc-ar}, |
| @command{gcc-nm}, @command{gcc-ranlib} wrappers to pass the right options |
| to these tools. With non fat LTO makefiles need to be modified to use them. |
| |
| The default is @option{-ffat-lto-objects} but this default is intended to |
| change in future releases when linker plugin enabled environments become more |
| common. |
| |
| @item -fcompare-elim |
| @opindex fcompare-elim |
| After register allocation and post-register allocation instruction splitting, |
| identify arithmetic instructions that compute processor flags similar to a |
| comparison operation based on that arithmetic. If possible, eliminate the |
| explicit comparison operation. |
| |
| This pass only applies to certain targets that cannot explicitly represent |
| the comparison operation before register allocation is complete. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fcprop-registers |
| @opindex fcprop-registers |
| After register allocation and post-register allocation instruction splitting, |
| perform a copy-propagation pass to try to reduce scheduling dependencies |
| and occasionally eliminate the copy. |
| |
| Enabled at levels @option{-O}, @option{-O2}, @option{-O3}, @option{-Os}. |
| |
| @item -fprofile-correction |
| @opindex fprofile-correction |
| Profiles collected using an instrumented binary for multi-threaded programs may |
| be inconsistent due to missed counter updates. When this option is specified, |
| GCC uses heuristics to correct or smooth out such inconsistencies. By |
| default, GCC emits an error message when an inconsistent profile is detected. |
| |
| @item -fprofile-dir=@var{path} |
| @opindex fprofile-dir |
| |
| Set the directory to search for the profile data files in to @var{path}. |
| This option affects only the profile data generated by |
| @option{-fprofile-generate}, @option{-ftest-coverage}, @option{-fprofile-arcs} |
| and used by @option{-fprofile-use} and @option{-fbranch-probabilities} |
| and its related options. Both absolute and relative paths can be used. |
| By default, GCC uses the current directory as @var{path}, thus the |
| profile data file appears in the same directory as the object file. |
| |
| @item -fprofile-generate |
| @itemx -fprofile-generate=@var{path} |
| @opindex fprofile-generate |
| |
| Enable options usually used for instrumenting application to produce |
| profile useful for later recompilation with profile feedback based |
| optimization. You must use @option{-fprofile-generate} both when |
| compiling and when linking your program. |
| |
| The following options are enabled: @code{-fprofile-arcs}, @code{-fprofile-values}, @code{-fvpt}. |
| |
| If @var{path} is specified, GCC looks at the @var{path} to find |
| the profile feedback data files. See @option{-fprofile-dir}. |
| |
| @item -fprofile-use |
| @itemx -fprofile-use=@var{path} |
| @opindex fprofile-use |
| Enable profile feedback directed optimizations, and optimizations |
| generally profitable only with profile feedback available. |
| |
| The following options are enabled: @code{-fbranch-probabilities}, @code{-fvpt}, |
| @code{-funroll-loops}, @code{-fpeel-loops}, @code{-ftracer} |
| |
| By default, GCC emits an error message if the feedback profiles do not |
| match the source code. This error can be turned into a warning by using |
| @option{-Wcoverage-mismatch}. Note this may result in poorly optimized |
| code. |
| |
| If @var{path} is specified, GCC looks at the @var{path} to find |
| the profile feedback data files. See @option{-fprofile-dir}. |
| @end table |
| |
| The following options control compiler behavior regarding floating-point |
| arithmetic. These options trade off between speed and |
| correctness. All must be specifically enabled. |
| |
| @table @gcctabopt |
| @item -ffloat-store |
| @opindex ffloat-store |
| Do not store floating-point variables in registers, and inhibit other |
| options that might change whether a floating-point value is taken from a |
| register or memory. |
| |
| @cindex floating-point precision |
| This option prevents undesirable excess precision on machines such as |
| the 68000 where the floating registers (of the 68881) keep more |
| precision than a @code{double} is supposed to have. Similarly for the |
| x86 architecture. For most programs, the excess precision does only |
| good, but a few programs rely on the precise definition of IEEE floating |
| point. Use @option{-ffloat-store} for such programs, after modifying |
| them to store all pertinent intermediate computations into variables. |
| |
| @item -fexcess-precision=@var{style} |
| @opindex fexcess-precision |
| This option allows further control over excess precision on machines |
| where floating-point registers have more precision than the IEEE |
| @code{float} and @code{double} types and the processor does not |
| support operations rounding to those types. By default, |
| @option{-fexcess-precision=fast} is in effect; this means that |
| operations are carried out in the precision of the registers and that |
| it is unpredictable when rounding to the types specified in the source |
| code takes place. When compiling C, if |
| @option{-fexcess-precision=standard} is specified then excess |
| precision follows the rules specified in ISO C99; in particular, |
| both casts and assignments cause values to be rounded to their |
| semantic types (whereas @option{-ffloat-store} only affects |
| assignments). This option is enabled by default for C if a strict |
| conformance option such as @option{-std=c99} is used. |
| |
| @opindex mfpmath |
| @option{-fexcess-precision=standard} is not implemented for languages |
| other than C, and has no effect if |
| @option{-funsafe-math-optimizations} or @option{-ffast-math} is |
| specified. On the x86, it also has no effect if @option{-mfpmath=sse} |
| or @option{-mfpmath=sse+387} is specified; in the former case, IEEE |
| semantics apply without excess precision, and in the latter, rounding |
| is unpredictable. |
| |
| @item -ffast-math |
| @opindex ffast-math |
| Sets @option{-fno-math-errno}, @option{-funsafe-math-optimizations}, |
| @option{-ffinite-math-only}, @option{-fno-rounding-math}, |
| @option{-fno-signaling-nans} and @option{-fcx-limited-range}. |
| |
| This option causes the preprocessor macro @code{__FAST_MATH__} to be defined. |
| |
| This option is not turned on by any @option{-O} option besides |
| @option{-Ofast} since it can result in incorrect output for programs |
| that depend on an exact implementation of IEEE or ISO rules/specifications |
| for math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| @item -fno-math-errno |
| @opindex fno-math-errno |
| Do not set @code{errno} after calling math functions that are executed |
| with a single instruction, e.g., @code{sqrt}. A program that relies on |
| IEEE exceptions for math error handling may want to use this flag |
| for speed while maintaining IEEE arithmetic compatibility. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| The default is @option{-fmath-errno}. |
| |
| On Darwin systems, the math library never sets @code{errno}. There is |
| therefore no reason for the compiler to consider the possibility that |
| it might, and @option{-fno-math-errno} is the default. |
| |
| @item -funsafe-math-optimizations |
| @opindex funsafe-math-optimizations |
| |
| Allow optimizations for floating-point arithmetic that (a) assume |
| that arguments and results are valid and (b) may violate IEEE or |
| ANSI standards. When used at link-time, it may include libraries |
| or startup files that change the default FPU control word or other |
| similar optimizations. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| Enables @option{-fno-signed-zeros}, @option{-fno-trapping-math}, |
| @option{-fassociative-math} and @option{-freciprocal-math}. |
| |
| The default is @option{-fno-unsafe-math-optimizations}. |
| |
| @item -fassociative-math |
| @opindex fassociative-math |
| |
| Allow re-association of operands in series of floating-point operations. |
| This violates the ISO C and C++ language standard by possibly changing |
| computation result. NOTE: re-ordering may change the sign of zero as |
| well as ignore NaNs and inhibit or create underflow or overflow (and |
| thus cannot be used on code that relies on rounding behavior like |
| @code{(x + 2**52) - 2**52}. May also reorder floating-point comparisons |
| and thus may not be used when ordered comparisons are required. |
| This option requires that both @option{-fno-signed-zeros} and |
| @option{-fno-trapping-math} be in effect. Moreover, it doesn't make |
| much sense with @option{-frounding-math}. For Fortran the option |
| is automatically enabled when both @option{-fno-signed-zeros} and |
| @option{-fno-trapping-math} are in effect. |
| |
| The default is @option{-fno-associative-math}. |
| |
| @item -freciprocal-math |
| @opindex freciprocal-math |
| |
| Allow the reciprocal of a value to be used instead of dividing by |
| the value if this enables optimizations. For example @code{x / y} |
| can be replaced with @code{x * (1/y)}, which is useful if @code{(1/y)} |
| is subject to common subexpression elimination. Note that this loses |
| precision and increases the number of flops operating on the value. |
| |
| The default is @option{-fno-reciprocal-math}. |
| |
| @item -ffinite-math-only |
| @opindex ffinite-math-only |
| Allow optimizations for floating-point arithmetic that assume |
| that arguments and results are not NaNs or +-Infs. |
| |
| This option is not turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. It may, however, yield faster code for programs |
| that do not require the guarantees of these specifications. |
| |
| The default is @option{-fno-finite-math-only}. |
| |
| @item -fno-signed-zeros |
| @opindex fno-signed-zeros |
| Allow optimizations for floating-point arithmetic that ignore the |
| signedness of zero. IEEE arithmetic specifies the behavior of |
| distinct +0.0 and @minus{}0.0 values, which then prohibits simplification |
| of expressions such as x+0.0 or 0.0*x (even with @option{-ffinite-math-only}). |
| This option implies that the sign of a zero result isn't significant. |
| |
| The default is @option{-fsigned-zeros}. |
| |
| @item -fno-trapping-math |
| @opindex fno-trapping-math |
| Compile code assuming that floating-point operations cannot generate |
| user-visible traps. These traps include division by zero, overflow, |
| underflow, inexact result and invalid operation. This option requires |
| that @option{-fno-signaling-nans} be in effect. Setting this option may |
| allow faster code if one relies on ``non-stop'' IEEE arithmetic, for example. |
| |
| This option should never be turned on by any @option{-O} option since |
| it can result in incorrect output for programs that depend on |
| an exact implementation of IEEE or ISO rules/specifications for |
| math functions. |
| |
| The default is @option{-ftrapping-math}. |
| |
| @item -frounding-math |
| @opindex frounding-math |
| Disable transformations and optimizations that assume default floating-point |
| rounding behavior. This is round-to-zero for all floating point |
| to integer conversions, and round-to-nearest for all other arithmetic |
| truncations. This option should be specified for programs that change |
| the FP rounding mode dynamically, or that may be executed with a |
| non-default rounding mode. This option disables constant folding of |
| floating-point expressions at compile time (which may be affected by |
| rounding mode) and arithmetic transformations that are unsafe in the |
| presence of sign-dependent rounding modes. |
| |
| The default is @option{-fno-rounding-math}. |
| |
| This option is experimental and does not currently guarantee to |
| disable all GCC optimizations that are affected by rounding mode. |
| Future versions of GCC may provide finer control of this setting |
| using C99's @code{FENV_ACCESS} pragma. This command-line option |
| will be used to specify the default state for @code{FENV_ACCESS}. |
| |
| @item -fsignaling-nans |
| @opindex fsignaling-nans |
| Compile code assuming that IEEE signaling NaNs may generate user-visible |
| traps during floating-point operations. Setting this option disables |
| optimizations that may change the number of exceptions visible with |
| signaling NaNs. This option implies @option{-ftrapping-math}. |
| |
| This option causes the preprocessor macro @code{__SUPPORT_SNAN__} to |
| be defined. |
| |
| The default is @option{-fno-signaling-nans}. |
| |
| This option is experimental and does not currently guarantee to |
| disable all GCC optimizations that affect signaling NaN behavior. |
| |
| @item -fsingle-precision-constant |
| @opindex fsingle-precision-constant |
| Treat floating-point constants as single precision instead of |
| implicitly converting them to double-precision constants. |
| |
| @item -fcx-limited-range |
| @opindex fcx-limited-range |
| When enabled, this option states that a range reduction step is not |
| needed when performing complex division. Also, there is no checking |
| whether the result of a complex multiplication or division is @code{NaN |
| + I*NaN}, with an attempt to rescue the situation in that case. The |
| default is @option{-fno-cx-limited-range}, but is enabled by |
| @option{-ffast-math}. |
| |
| This option controls the default setting of the ISO C99 |
| @code{CX_LIMITED_RANGE} pragma. Nevertheless, the option applies to |
| all languages. |
| |
| @item -fcx-fortran-rules |
| @opindex fcx-fortran-rules |
| Complex multiplication and division follow Fortran rules. Range |
| reduction is done as part of complex division, but there is no checking |
| whether the result of a complex multiplication or division is @code{NaN |
| + I*NaN}, with an attempt to rescue the situation in that case. |
| |
| The default is @option{-fno-cx-fortran-rules}. |
| |
| @end table |
| |
| The following options control optimizations that may improve |
| performance, but are not enabled by any @option{-O} options. This |
| section includes experimental options that may produce broken code. |
| |
| @table @gcctabopt |
| @item -fbranch-probabilities |
| @opindex fbranch-probabilities |
| After running a program compiled with @option{-fprofile-arcs} |
| (@pxref{Debugging Options,, Options for Debugging Your Program or |
| @command{gcc}}), you can compile it a second time using |
| @option{-fbranch-probabilities}, to improve optimizations based on |
| the number of times each branch was taken. When a program |
| compiled with @option{-fprofile-arcs} exits, it saves arc execution |
| counts to a file called @file{@var{sourcename}.gcda} for each source |
| file. The information in this data file is very dependent on the |
| structure of the generated code, so you must use the same source code |
| and the same optimization options for both compilations. |
| |
| With @option{-fbranch-probabilities}, GCC puts a |
| @samp{REG_BR_PROB} note on each @samp{JUMP_INSN} and @samp{CALL_INSN}. |
| These can be used to improve optimization. Currently, they are only |
| used in one place: in @file{reorg.c}, instead of guessing which path a |
| branch is most likely to take, the @samp{REG_BR_PROB} values are used to |
| exactly determine which path is taken more often. |
| |
| @item -fprofile-values |
| @opindex fprofile-values |
| If combined with @option{-fprofile-arcs}, it adds code so that some |
| data about values of expressions in the program is gathered. |
| |
| With @option{-fbranch-probabilities}, it reads back the data gathered |
| from profiling values of expressions for usage in optimizations. |
| |
| Enabled with @option{-fprofile-generate} and @option{-fprofile-use}. |
| |
| @item -fvpt |
| @opindex fvpt |
| If combined with @option{-fprofile-arcs}, this option instructs the compiler |
| to add code to gather information about values of expressions. |
| |
| With @option{-fbranch-probabilities}, it reads back the data gathered |
| and actually performs the optimizations based on them. |
| Currently the optimizations include specialization of division operations |
| using the knowledge about the value of the denominator. |
| |
| @item -frename-registers |
| @opindex frename-registers |
| Attempt to avoid false dependencies in scheduled code by making use |
| of registers left over after register allocation. This optimization |
| most benefits processors with lots of registers. Depending on the |
| debug information format adopted by the target, however, it can |
| make debugging impossible, since variables no longer stay in |
| a ``home register''. |
| |
| Enabled by default with @option{-funroll-loops} and @option{-fpeel-loops}. |
| |
| @item -ftracer |
| @opindex ftracer |
| Perform tail duplication to enlarge superblock size. This transformation |
| simplifies the control flow of the function allowing other optimizations to do |
| a better job. |
| |
| Enabled with @option{-fprofile-use}. |
| |
| @item -funroll-loops |
| @opindex funroll-loops |
| Unroll loops whose number of iterations can be determined at compile time or |
| upon entry to the loop. @option{-funroll-loops} implies |
| @option{-frerun-cse-after-loop}, @option{-fweb} and @option{-frename-registers}. |
| It also turns on complete loop peeling (i.e.@: complete removal of loops with |
| a small constant number of iterations). This option makes code larger, and may |
| or may not make it run faster. |
| |
| Enabled with @option{-fprofile-use}. |
| |
| @item -funroll-all-loops |
| @opindex funroll-all-loops |
| Unroll all loops, even if their number of iterations is uncertain when |
| the loop is entered. This usually makes programs run more slowly. |
| @option{-funroll-all-loops} implies the same options as |
| @option{-funroll-loops}. |
| |
| @item -fpeel-loops |
| @opindex fpeel-loops |
| Peels loops for which there is enough information that they do not |
| roll much (from profile feedback). It also turns on complete loop peeling |
| (i.e.@: complete removal of loops with small constant number of iterations). |
| |
| Enabled with @option{-fprofile-use}. |
| |
| @item -fmove-loop-invariants |
| @opindex fmove-loop-invariants |
| Enables the loop invariant motion pass in the RTL loop optimizer. Enabled |
| at level @option{-O1} |
| |
| @item -funswitch-loops |
| @opindex funswitch-loops |
| Move branches with loop invariant conditions out of the loop, with duplicates |
| of the loop on both branches (modified according to result of the condition). |
| |
| @item -ffunction-sections |
| @itemx -fdata-sections |
| @opindex ffunction-sections |
| @opindex fdata-sections |
| Place each function or data item into its own section in the output |
| file if the target supports arbitrary sections. The name of the |
| function or the name of the data item determines the section's name |
| in the output file. |
| |
| Use these options on systems where the linker can perform optimizations |
| to improve locality of reference in the instruction space. Most systems |
| using the ELF object format and SPARC processors running Solaris 2 have |
| linkers with such optimizations. AIX may have these optimizations in |
| the future. |
| |
| Only use these options when there are significant benefits from doing |
| so. When you specify these options, the assembler and linker |
| create larger object and executable files and are also slower. |
| You cannot use @code{gprof} on all systems if you |
| specify this option, and you may have problems with debugging if |
| you specify both this option and @option{-g}. |
| |
| @item -fbranch-target-load-optimize |
| @opindex fbranch-target-load-optimize |
| Perform branch target register load optimization before prologue / epilogue |
| threading. |
| The use of target registers can typically be exposed only during reload, |
| thus hoisting loads out of loops and doing inter-block scheduling needs |
| a separate optimization pass. |
| |
| @item -fbranch-target-load-optimize2 |
| @opindex fbranch-target-load-optimize2 |
| Perform branch target register load optimization after prologue / epilogue |
| threading. |
| |
| @item -fbtr-bb-exclusive |
| @opindex fbtr-bb-exclusive |
| When performing branch target register load optimization, don't reuse |
| branch target registers within any basic block. |
| |
| @item -fstack-protector |
| @opindex fstack-protector |
| Emit extra code to check for buffer overflows, such as stack smashing |
| attacks. This is done by adding a guard variable to functions with |
| vulnerable objects. This includes functions that call @code{alloca}, and |
| functions with buffers larger than 8 bytes. The guards are initialized |
| when a function is entered and then checked when the function exits. |
| If a guard check fails, an error message is printed and the program exits. |
| |
| @item -fstack-protector-all |
| @opindex fstack-protector-all |
| Like @option{-fstack-protector} except that all functions are protected. |
| |
| @item -fsection-anchors |
| @opindex fsection-anchors |
| Try to reduce the number of symbolic address calculations by using |
| shared ``anchor'' symbols to address nearby objects. This transformation |
| can help to reduce the number of GOT entries and GOT accesses on some |
| targets. |
| |
| For example, the implementation of the following function @code{foo}: |
| |
| @smallexample |
| static int a, b, c; |
| int foo (void) @{ return a + b + c; @} |
| @end smallexample |
| |
| @noindent |
| usually calculates the addresses of all three variables, but if you |
| compile it with @option{-fsection-anchors}, it accesses the variables |
| from a common anchor point instead. The effect is similar to the |
| following pseudocode (which isn't valid C): |
| |
| @smallexample |
| int foo (void) |
| @{ |
| register int *xr = &x; |
| return xr[&a - &x] + xr[&b - &x] + xr[&c - &x]; |
| @} |
| @end smallexample |
| |
| Not all targets support this option. |
| |
| @item --param @var{name}=@var{value} |
| @opindex param |
| In some places, GCC uses various constants to control the amount of |
| optimization that is done. For example, GCC does not inline functions |
| that contain more than a certain number of instructions. You can |
| control some of these constants on the command line using the |
| @option{--param} option. |
| |
| The names of specific parameters, and the meaning of the values, are |
| tied to the internals of the compiler, and are subject to change |
| without notice in future releases. |
| |
| In each case, the @var{value} is an integer. The allowable choices for |
| @var{name} are: |
| |
| @table @gcctabopt |
| @item predictable-branch-outcome |
| When branch is predicted to be taken with probability lower than this threshold |
| (in percent), then it is considered well predictable. The default is 10. |
| |
| @item max-crossjump-edges |
| The maximum number of incoming edges to consider for cross-jumping. |
| The algorithm used by @option{-fcrossjumping} is @math{O(N^2)} in |
| the number of edges incoming to each block. Increasing values mean |
| more aggressive optimization, making the compilation time increase with |
| probably small improvement in executable size. |
| |
| @item min-crossjump-insns |
| The minimum number of instructions that must be matched at the end |
| of two blocks before cross-jumping is performed on them. This |
| value is ignored in the case where all instructions in the block being |
| cross-jumped from are matched. The default value is 5. |
| |
| @item max-grow-copy-bb-insns |
| The maximum code size expansion factor when copying basic blocks |
| instead of jumping. The expansion is relative to a jump instruction. |
| The default value is 8. |
| |
| @item max-goto-duplication-insns |
| The maximum number of instructions to duplicate to a block that jumps |
| to a computed goto. To avoid @math{O(N^2)} behavior in a number of |
| passes, GCC factors computed gotos early in the compilation process, |
| and unfactors them as late as possible. Only computed jumps at the |
| end of a basic blocks with no more than max-goto-duplication-insns are |
| unfactored. The default value is 8. |
| |
| @item max-delay-slot-insn-search |
| The maximum number of instructions to consider when looking for an |
| instruction to fill a delay slot. If more than this arbitrary number of |
| instructions are searched, the time savings from filling the delay slot |
| are minimal, so stop searching. Increasing values mean more |
| aggressive optimization, making the compilation time increase with probably |
| small improvement in execution time. |
| |
| @item max-delay-slot-live-search |
| When trying to fill delay slots, the maximum number of instructions to |
| consider when searching for a block with valid live register |
| information. Increasing this arbitrarily chosen value means more |
| aggressive optimization, increasing the compilation time. This parameter |
| should be removed when the delay slot code is rewritten to maintain the |
| control-flow graph. |
| |
| @item max-gcse-memory |
| The approximate maximum amount of memory that can be allocated in |
| order to perform the global common subexpression elimination |
| optimization. If more memory than specified is required, the |
| optimization is not done. |
| |
| @item max-gcse-insertion-ratio |
| If the ratio of expression insertions to deletions is larger than this value |
| for any expression, then RTL PRE inserts or removes the expression and thus |
| leaves partially redundant computations in the instruction stream. The default value is 20. |
| |
| @item max-pending-list-length |
| The maximum number of pending dependencies scheduling allows |
| before flushing the current state and starting over. Large functions |
| with few branches or calls can create excessively large lists which |
| needlessly consume memory and resources. |
| |
| @item max-modulo-backtrack-attempts |
| The maximum number of backtrack attempts the scheduler should make |
| when modulo scheduling a loop. Larger values can exponentially increase |
| compilation time. |
| |
| @item max-inline-insns-single |
| Several parameters control the tree inliner used in GCC@. |
| This number sets the maximum number of instructions (counted in GCC's |
| internal representation) in a single function that the tree inliner |
| considers for inlining. This only affects functions declared |
| inline and methods implemented in a class declaration (C++). |
| The default value is 400. |
| |
| @item max-inline-insns-auto |
| When you use @option{-finline-functions} (included in @option{-O3}), |
| a lot of functions that would otherwise not be considered for inlining |
| by the compiler are investigated. To those functions, a different |
| (more restrictive) limit compared to functions declared inline can |
| be applied. |
| The default value is 40. |
| |
| @item large-function-insns |
| The limit specifying really large functions. For functions larger than this |
| limit after inlining, inlining is constrained by |
| @option{--param large-function-growth}. This parameter is useful primarily |
| to avoid extreme compilation time caused by non-linear algorithms used by the |
| back end. |
| The default value is 2700. |
| |
| @item large-function-growth |
| Specifies maximal growth of large function caused by inlining in percents. |
| The default value is 100 which limits large function growth to 2.0 times |
| the original size. |
| |
| @item large-unit-insns |
| The limit specifying large translation unit. Growth caused by inlining of |
| units larger than this limit is limited by @option{--param inline-unit-growth}. |
| For small units this might be too tight. |
| For example, consider a unit consisting of function A |
| that is inline and B that just calls A three times. If B is small relative to |
| A, the growth of unit is 300\% and yet such inlining is very sane. For very |
| large units consisting of small inlineable functions, however, the overall unit |
| growth limit is needed to avoid exponential explosion of code size. Thus for |
| smaller units, the size is increased to @option{--param large-unit-insns} |
| before applying @option{--param inline-unit-growth}. The default is 10000. |
| |
| @item inline-unit-growth |
| Specifies maximal overall growth of the compilation unit caused by inlining. |
| The default value is 30 which limits unit growth to 1.3 times the original |
| size. |
| |
| @item ipcp-unit-growth |
| Specifies maximal overall growth of the compilation unit caused by |
| interprocedural constant propagation. The default value is 10 which limits |
| unit growth to 1.1 times the original size. |
| |
| @item large-stack-frame |
| The limit specifying large stack frames. While inlining the algorithm is trying |
| to not grow past this limit too much. The default value is 256 bytes. |
| |
| @item large-stack-frame-growth |
| Specifies maximal growth of large stack frames caused by inlining in percents. |
| The default value is 1000 which limits large stack frame growth to 11 times |
| the original size. |
| |
| @item max-inline-insns-recursive |
| @itemx max-inline-insns-recursive-auto |
| Specifies the maximum number of instructions an out-of-line copy of a |
| self-recursive inline |
| function can grow into by performing recursive inlining. |
| |
| For functions declared inline, @option{--param max-inline-insns-recursive} is |
| taken into account. For functions not declared inline, recursive inlining |
| happens only when @option{-finline-functions} (included in @option{-O3}) is |
| enabled and @option{--param max-inline-insns-recursive-auto} is used. The |
| default value is 450. |
| |
| @item max-inline-recursive-depth |
| @itemx max-inline-recursive-depth-auto |
| Specifies the maximum recursion depth used for recursive inlining. |
| |
| For functions declared inline, @option{--param max-inline-recursive-depth} is |
| taken into account. For functions not declared inline, recursive inlining |
| happens only when @option{-finline-functions} (included in @option{-O3}) is |
| enabled and @option{--param max-inline-recursive-depth-auto} is used. The |
| default value is 8. |
| |
| @item min-inline-recursive-probability |
| Recursive inlining is profitable only for function having deep recursion |
| in average and can hurt for function having little recursion depth by |
| increasing the prologue size or complexity of function body to other |
| optimizers. |
| |
| When profile feedback is available (see @option{-fprofile-generate}) the actual |
| recursion depth can be guessed from probability that function recurses via a |
| given call expression. This parameter limits inlining only to call expressions |
| whose probability exceeds the given threshold (in percents). |
| The default value is 10. |
| |
| @item early-inlining-insns |
| Specify growth that the early inliner can make. In effect it increases |
| the amount of inlining for code having a large abstraction penalty. |
| The default value is 10. |
| |
| @item max-early-inliner-iterations |
| @itemx max-early-inliner-iterations |
| Limit of iterations of the early inliner. This basically bounds |
| the number of nested indirect calls the early inliner can resolve. |
| Deeper chains are still handled by late inlining. |
| |
| @item comdat-sharing-probability |
| @itemx comdat-sharing-probability |
| Probability (in percent) that C++ inline function with comdat visibility |
| are shared across multiple compilation units. The default value is 20. |
| |
| @item min-vect-loop-bound |
| The minimum number of iterations under which loops are not vectorized |
| when @option{-ftree-vectorize} is used. The number of iterations after |
| vectorization needs to be greater than the value specified by this option |
| to allow vectorization. The default value is 0. |
| |
| @item gcse-cost-distance-ratio |
| Scaling factor in calculation of maximum distance an expression |
| can be moved by GCSE optimizations. This is currently supported only in the |
| code hoisting pass. The bigger the ratio, the more aggressive code hoisting |
| is with simple expressions, i.e., the expressions that have cost |
| less than @option{gcse-unrestricted-cost}. Specifying 0 disables |
| hoisting of simple expressions. The default value is 10. |
| |
| @item gcse-unrestricted-cost |
| Cost, roughly measured as the cost of a single typical machine |
| instruction, at which GCSE optimizations do not constrain |
| the distance an expression can travel. This is currently |
| supported only in the code hoisting pass. The lesser the cost, |
| the more aggressive code hoisting is. Specifying 0 |
| allows all expressions to travel unrestricted distances. |
| The default value is 3. |
| |
| @item max-hoist-depth |
| The depth of search in the dominator tree for expressions to hoist. |
| This is used to avoid quadratic behavior in hoisting algorithm. |
| The value of 0 does not limit on the search, but may slow down compilation |
| of huge functions. The default value is 30. |
| |
| @item max-tail-merge-comparisons |
| The maximum amount of similar bbs to compare a bb with. This is used to |
| avoid quadratic behavior in tree tail merging. The default value is 10. |
| |
| @item max-tail-merge-iterations |
| The maximum amount of iterations of the pass over the function. This is used to |
| limit compilation time in tree tail merging. The default value is 2. |
| |
| @item max-unrolled-insns |
| The maximum number of instructions that a loop may have to be unrolled. |
| If a loop is unrolled, this parameter also determines how many times |
| the loop code is unrolled. |
| |
| @item max-average-unrolled-insns |
| The maximum number of instructions biased by probabilities of their execution |
| that a loop may have to be unrolled. If a loop is unrolled, |
| this parameter also determines how many times the loop code is unrolled. |
| |
| @item max-unroll-times |
| The maximum number of unrollings of a single loop. |
| |
| @item max-peeled-insns |
| The maximum number of instructions that a loop may have to be peeled. |
| If a loop is peeled, this parameter also determines how many times |
| the loop code is peeled. |
| |
| @item max-peel-times |
| The maximum number of peelings of a single loop. |
| |
| @item max-completely-peeled-insns |
| The maximum number of insns of a completely peeled loop. |
| |
| @item max-completely-peel-times |
| The maximum number of iterations of a loop to be suitable for complete peeling. |
| |
| @item max-completely-peel-loop-nest-depth |
| The maximum depth of a loop nest suitable for complete peeling. |
| |
| @item max-unswitch-insns |
| The maximum number of insns of an unswitched loop. |
| |
| @item max-unswitch-level |
| The maximum number of branches unswitched in a single loop. |
| |
| @item lim-expensive |
| The minimum cost of an expensive expression in the loop invariant motion. |
| |
| @item iv-consider-all-candidates-bound |
| Bound on number of candidates for induction variables, below which |
| all candidates are considered for each use in induction variable |
| optimizations. If there are more candidates than this, |
| only the most relevant ones are considered to avoid quadratic time complexity. |
| |
| @item iv-max-considered-uses |
| The induction variable optimizations give up on loops that contain more |
| induction variable uses. |
| |
| @item iv-always-prune-cand-set-bound |
| If the number of candidates in the set is smaller than this value, |
| always try to remove unnecessary ivs from the set |
| when adding a new one. |
| |
| @item scev-max-expr-size |
| Bound on size of expressions used in the scalar evolutions analyzer. |
| Large expressions slow the analyzer. |
| |
| @item scev-max-expr-complexity |
| Bound on the complexity of the expressions in the scalar evolutions analyzer. |
| Complex expressions slow the analyzer. |
| |
| @item omega-max-vars |
| The maximum number of variables in an Omega constraint system. |
| The default value is 128. |
| |
| @item omega-max-geqs |
| The maximum number of inequalities in an Omega constraint system. |
| The default value is 256. |
| |
| @item omega-max-eqs |
| The maximum number of equalities in an Omega constraint system. |
| The default value is 128. |
| |
| @item omega-max-wild-cards |
| The maximum number of wildcard variables that the Omega solver is |
| able to insert. The default value is 18. |
| |
| @item omega-hash-table-size |
| The size of the hash table in the Omega solver. The default value is |
| 550. |
| |
| @item omega-max-keys |
| The maximal number of keys used by the Omega solver. The default |
| value is 500. |
| |
| @item omega-eliminate-redundant-constraints |
| When set to 1, use expensive methods to eliminate all redundant |
| constraints. The default value is 0. |
| |
| @item vect-max-version-for-alignment-checks |
| The maximum number of run-time checks that can be performed when |
| doing loop versioning for alignment in the vectorizer. See option |
| @option{-ftree-vect-loop-version} for more information. |
| |
| @item vect-max-version-for-alias-checks |
| The maximum number of run-time checks that can be performed when |
| doing loop versioning for alias in the vectorizer. See option |
| @option{-ftree-vect-loop-version} for more information. |
| |
| @item max-iterations-to-track |
| The maximum number of iterations of a loop the brute-force algorithm |
| for analysis of the number of iterations of the loop tries to evaluate. |
| |
| @item hot-bb-count-fraction |
| Select fraction of the maximal count of repetitions of basic block in program |
| given basic block needs to have to be considered hot. |
| |
| @item hot-bb-frequency-fraction |
| Select fraction of the entry block frequency of executions of basic block in |
| function given basic block needs to have to be considered hot. |
| |
| @item max-predicted-iterations |
| The maximum number of loop iterations we predict statically. This is useful |
| in cases where a function contains a single loop with known bound and |
| another loop with unknown bound. |
| The known number of iterations is predicted correctly, while |
| the unknown number of iterations average to roughly 10. This means that the |
| loop without bounds appears artificially cold relative to the other one. |
| |
| @item align-threshold |
| |
| Select fraction of the maximal frequency of executions of a basic block in |
| a function to align the basic block. |
| |
| @item align-loop-iterations |
| |
| A loop expected to iterate at least the selected number of iterations is |
| aligned. |
| |
| @item tracer-dynamic-coverage |
| @itemx tracer-dynamic-coverage-feedback |
| |
| This value is used to limit superblock formation once the given percentage of |
| executed instructions is covered. This limits unnecessary code size |
| expansion. |
| |
| The @option{tracer-dynamic-coverage-feedback} is used only when profile |
| feedback is available. The real profiles (as opposed to statically estimated |
| ones) are much less balanced allowing the threshold to be larger value. |
| |
| @item tracer-max-code-growth |
| Stop tail duplication once code growth has reached given percentage. This is |
| a rather artificial limit, as most of the duplicates are eliminated later in |
| cross jumping, so it may be set to much higher values than is the desired code |
| growth. |
| |
| @item tracer-min-branch-ratio |
| |
| Stop reverse growth when the reverse probability of best edge is less than this |
| threshold (in percent). |
| |
| @item tracer-min-branch-ratio |
| @itemx tracer-min-branch-ratio-feedback |
| |
| Stop forward growth if the best edge has probability lower than this |
| threshold. |
| |
| Similarly to @option{tracer-dynamic-coverage} two values are present, one for |
| compilation for profile feedback and one for compilation without. The value |
| for compilation with profile feedback needs to be more conservative (higher) in |
| order to make tracer effective. |
| |
| @item max-cse-path-length |
| |
| The maximum number of basic blocks on path that CSE considers. |
| The default is 10. |
| |
| @item max-cse-insns |
| The maximum number of instructions CSE processes before flushing. |
| The default is 1000. |
| |
| @item ggc-min-expand |
| |
| GCC uses a garbage collector to manage its own memory allocation. This |
| parameter specifies the minimum percentage by which the garbage |
| collector's heap should be allowed to expand between collections. |
| Tuning this may improve compilation speed; it has no effect on code |
| generation. |
| |
| The default is 30% + 70% * (RAM/1GB) with an upper bound of 100% when |
| RAM >= 1GB@. If @code{getrlimit} is available, the notion of ``RAM'' is |
| the smallest of actual RAM and @code{RLIMIT_DATA} or @code{RLIMIT_AS}. If |
| GCC is not able to calculate RAM on a particular platform, the lower |
| bound of 30% is used. Setting this parameter and |
| @option{ggc-min-heapsize} to zero causes a full collection to occur at |
| every opportunity. This is extremely slow, but can be useful for |
| debugging. |
| |
| @item ggc-min-heapsize |
| |
| Minimum size of the garbage collector's heap before it begins bothering |
| to collect garbage. The first collection occurs after the heap expands |
| by @option{ggc-min-expand}% beyond @option{ggc-min-heapsize}. Again, |
| tuning this may improve compilation speed, and has no effect on code |
| generation. |
| |
| The default is the smaller of RAM/8, RLIMIT_RSS, or a limit that |
| tries to ensure that RLIMIT_DATA or RLIMIT_AS are not exceeded, but |
| with a lower bound of 4096 (four megabytes) and an upper bound of |
| 131072 (128 megabytes). If GCC is not able to calculate RAM on a |
| particular platform, the lower bound is used. Setting this parameter |
| very large effectively disables garbage collection. Setting this |
| parameter and @option{ggc-min-expand} to zero causes a full collection |
| to occur at every opportunity. |
| |
| @item max-reload-search-insns |
| The maximum number of instruction reload should look backward for equivalent |
| register. Increasing values mean more aggressive optimization, making the |
| compilation time increase with probably slightly better performance. |
| The default value is 100. |
| |
| @item max-cselib-memory-locations |
| The maximum number of memory locations cselib should take into account. |
| Increasing values mean more aggressive optimization, making the compilation time |
| increase with probably slightly better performance. The default value is 500. |
| |
| @item reorder-blocks-duplicate |
| @itemx reorder-blocks-duplicate-feedback |
| |
| Used by the basic block reordering pass to decide whether to use unconditional |
| branch or duplicate the code on its destination. Code is duplicated when its |
| estimated size is smaller than this value multiplied by the estimated size of |
| unconditional jump in the hot spots of the program. |
| |
| The @option{reorder-block-duplicate-feedback} is used only when profile |
| feedback is available. It may be set to higher values than |
| @option{reorder-block-duplicate} since information about the hot spots is more |
| accurate. |
| |
| @item max-sched-ready-insns |
| The maximum number of instructions ready to be issued the scheduler should |
| consider at any given time during the first scheduling pass. Increasing |
| values mean more thorough searches, making the compilation time increase |
| with probably little benefit. The default value is 100. |
| |
| @item max-sched-region-blocks |
| The maximum number of blocks in a region to be considered for |
| interblock scheduling. The default value is 10. |
| |
| @item max-pipeline-region-blocks |
| The maximum number of blocks in a region to be considered for |
| pipelining in the selective scheduler. The default value is 15. |
| |
| @item max-sched-region-insns |
| The maximum number of insns in a region to be considered for |
| interblock scheduling. The default value is 100. |
| |
| @item max-pipeline-region-insns |
| The maximum number of insns in a region to be considered for |
| pipelining in the selective scheduler. The default value is 200. |
| |
| @item min-spec-prob |
| The minimum probability (in percents) of reaching a source block |
| for interblock speculative scheduling. The default value is 40. |
| |
| @item max-sched-extend-regions-iters |
| The maximum number of iterations through CFG to extend regions. |
| A value of 0 (the default) disables region extensions. |
| |
| @item max-sched-insn-conflict-delay |
| The maximum conflict delay for an insn to be considered for speculative motion. |
| The default value is 3. |
| |
| @item sched-spec-prob-cutoff |
| The minimal probability of speculation success (in percents), so that |
| speculative insns are scheduled. |
| The default value is 40. |
| |
| @item sched-mem-true-dep-cost |
| Minimal distance (in CPU cycles) between store and load targeting same |
| memory locations. The default value is 1. |
| |
| @item selsched-max-lookahead |
| The maximum size of the lookahead window of selective scheduling. It is a |
| depth of search for available instructions. |
| The default value is 50. |
| |
| @item selsched-max-sched-times |
| The maximum number of times that an instruction is scheduled during |
| selective scheduling. This is the limit on the number of iterations |
| through which the instruction may be pipelined. The default value is 2. |
| |
| @item selsched-max-insns-to-rename |
| The maximum number of best instructions in the ready list that are considered |
| for renaming in the selective scheduler. The default value is 2. |
| |
| @item sms-min-sc |
| The minimum value of stage count that swing modulo scheduler |
| generates. The default value is 2. |
| |
| @item max-last-value-rtl |
| The maximum size measured as number of RTLs that can be recorded in an expression |
| in combiner for a pseudo register as last known value of that register. The default |
| is 10000. |
| |
| @item integer-share-limit |
| Small integer constants can use a shared data structure, reducing the |
| compiler's memory usage and increasing its speed. This sets the maximum |
| value of a shared integer constant. The default value is 256. |
| |
| @item ssp-buffer-size |
| The minimum size of buffers (i.e.@: arrays) that receive stack smashing |
| protection when @option{-fstack-protection} is used. |
| |
| @item max-jump-thread-duplication-stmts |
| Maximum number of statements allowed in a block that needs to be |
| duplicated when threading jumps. |
| |
| @item max-fields-for-field-sensitive |
| Maximum number of fields in a structure treated in |
| a field sensitive manner during pointer analysis. The default is zero |
| for @option{-O0} and @option{-O1}, |
| and 100 for @option{-Os}, @option{-O2}, and @option{-O3}. |
| |
| @item prefetch-latency |
| Estimate on average number of instructions that are executed before |
| prefetch finishes. The distance prefetched ahead is proportional |
| to this constant. Increasing this number may also lead to less |
| streams being prefetched (see @option{simultaneous-prefetches}). |
| |
| @item simultaneous-prefetches |
| Maximum number of prefetches that can run at the same time. |
| |
| @item l1-cache-line-size |
| The size of cache line in L1 cache, in bytes. |
| |
| @item l1-cache-size |
| The size of L1 cache, in kilobytes. |
| |
| @item l2-cache-size |
| The size of L2 cache, in kilobytes. |
| |
| @item min-insn-to-prefetch-ratio |
| The minimum ratio between the number of instructions and the |
| number of prefetches to enable prefetching in a loop. |
| |
| @item prefetch-min-insn-to-mem-ratio |
| The minimum ratio between the number of instructions and the |
| number of memory references to enable prefetching in a loop. |
| |
| @item use-canonical-types |
| Whether the compiler should use the ``canonical'' type system. By |
| default, this should always be 1, which uses a more efficient internal |
| mechanism for comparing types in C++ and Objective-C++. However, if |
| bugs in the canonical type system are causing compilation failures, |
| set this value to 0 to disable canonical types. |
| |
| @item switch-conversion-max-branch-ratio |
| Switch initialization conversion refuses to create arrays that are |
| bigger than @option{switch-conversion-max-branch-ratio} times the number of |
| branches in the switch. |
| |
| @item max-partial-antic-length |
| Maximum length of the partial antic set computed during the tree |
| partial redundancy elimination optimization (@option{-ftree-pre}) when |
| optimizing at @option{-O3} and above. For some sorts of source code |
| the enhanced partial redundancy elimination optimization can run away, |
| consuming all of the memory available on the host machine. This |
| parameter sets a limit on the length of the sets that are computed, |
| which prevents the runaway behavior. Setting a value of 0 for |
| this parameter allows an unlimited set length. |
| |
| @item sccvn-max-scc-size |
| Maximum size of a strongly connected component (SCC) during SCCVN |
| processing. If this limit is hit, SCCVN processing for the whole |
| function is not done and optimizations depending on it are |
| disabled. The default maximum SCC size is 10000. |
| |
| @item sccvn-max-alias-queries-per-access |
| Maximum number of alias-oracle queries we perform when looking for |
| redundancies for loads and stores. If this limit is hit the search |
| is aborted and the load or store is not considered redundant. The |
| number of queries is algorithmically limited to the number of |
| stores on all paths from the load to the function entry. |
| The default maxmimum number of queries is 1000. |
| |
| @item ira-max-loops-num |
| IRA uses regional register allocation by default. If a function |
| contains more loops than the number given by this parameter, only at most |
| the given number of the most frequently-executed loops form regions |
| for regional register allocation. The default value of the |
| parameter is 100. |
| |
| @item ira-max-conflict-table-size |
| Although IRA uses a sophisticated algorithm to compress the conflict |
| table, the table can still require excessive amounts of memory for |
| huge functions. If the conflict table for a function could be more |
| than the size in MB given by this parameter, the register allocator |
| instead uses a faster, simpler, and lower-quality |
| algorithm that does not require building a pseudo-register conflict table. |
| The default value of the parameter is 2000. |
| |
| @item ira-loop-reserved-regs |
| IRA can be used to evaluate more accurate register pressure in loops |
| for decisions to move loop invariants (see @option{-O3}). The number |
| of available registers reserved for some other purposes is given |
| by this parameter. The default value of the parameter is 2, which is |
| the minimal number of registers needed by typical instructions. |
| This value is the best found from numerous experiments. |
| |
| @item loop-invariant-max-bbs-in-loop |
| Loop invariant motion can be very expensive, both in compilation time and |
| in amount of needed compile-time memory, with very large loops. Loops |
| with more basic blocks than this parameter won't have loop invariant |
| motion optimization performed on them. The default value of the |
| parameter is 1000 for @option{-O1} and 10000 for @option{-O2} and above. |
| |
| @item loop-max-datarefs-for-datadeps |
| Building data dapendencies is expensive for very large loops. This |
| parameter limits the number of data references in loops that are |
| considered for data dependence analysis. These large loops are no |
| handled by the optimizations using loop data dependencies. |
| The default value is 1000. |
| |
| @item max-vartrack-size |
| Sets a maximum number of hash table slots to use during variable |
| tracking dataflow analysis of any function. If this limit is exceeded |
| with variable tracking at assignments enabled, analysis for that |
| function is retried without it, after removing all debug insns from |
| the function. If the limit is exceeded even without debug insns, var |
| tracking analysis is completely disabled for the function. Setting |
| the parameter to zero makes it unlimited. |
| |
| @item max-vartrack-expr-depth |
| Sets a maximum number of recursion levels when attempting to map |
| variable names or debug temporaries to value expressions. This trades |
| compilation time for more complete debug information. If this is set too |
| low, value expressions that are available and could be represented in |
| debug information may end up not being used; setting this higher may |
| enable the compiler to find more complex debug expressions, but compile |
| time and memory use may grow. The default is 12. |
| |
| @item min-nondebug-insn-uid |
| Use uids starting at this parameter for nondebug insns. The range below |
| the parameter is reserved exclusively for debug insns created by |
| @option{-fvar-tracking-assignments}, but debug insns may get |
| (non-overlapping) uids above it if the reserved range is exhausted. |
| |
| @item ipa-sra-ptr-growth-factor |
| IPA-SRA replaces a pointer to an aggregate with one or more new |
| parameters only when their cumulative size is less or equal to |
| @option{ipa-sra-ptr-growth-factor} times the size of the original |
| pointer parameter. |
| |
| @item tm-max-aggregate-size |
| When making copies of thread-local variables in a transaction, this |
| parameter specifies the size in bytes after which variables are |
| saved with the logging functions as opposed to save/restore code |
| sequence pairs. This option only applies when using |
| @option{-fgnu-tm}. |
| |
| @item graphite-max-nb-scop-params |
| To avoid exponential effects in the Graphite loop transforms, the |
| number of parameters in a Static Control Part (SCoP) is bounded. The |
| default value is 10 parameters. A variable whose value is unknown at |
| compilation time and defined outside a SCoP is a parameter of the SCoP. |
| |
| @item graphite-max-bbs-per-function |
| To avoid exponential effects in the detection of SCoPs, the size of |
| the functions analyzed by Graphite is bounded. The default value is |
| 100 basic blocks. |
| |
| @item loop-block-tile-size |
| Loop blocking or strip mining transforms, enabled with |
| @option{-floop-block} or @option{-floop-strip-mine}, strip mine each |
| loop in the loop nest by a given number of iterations. The strip |
| length can be changed using the @option{loop-block-tile-size} |
| parameter. The default value is 51 iterations. |
| |
| @item ipa-cp-value-list-size |
| IPA-CP attempts to track all possible values and types passed to a function's |
| parameter in order to propagate them and perform devirtualization. |
| @option{ipa-cp-value-list-size} is the maximum number of values and types it |
| stores per one formal parameter of a function. |
| |
| @item lto-partitions |
| Specify desired number of partitions produced during WHOPR compilation. |
| The number of partitions should exceed the number of CPUs used for compilation. |
| The default value is 32. |
| |
| @item lto-minpartition |
| Size of minimal partition for WHOPR (in estimated instructions). |
| This prevents expenses of splitting very small programs into too many |
| partitions. |
| |
| @item cxx-max-namespaces-for-diagnostic-help |
| The maximum number of namespaces to consult for suggestions when C++ |
| name lookup fails for an identifier. The default is 1000. |
| |
| @item sink-frequency-threshold |
| The maximum relative execution frequency (in percents) of the target block |
| relative to a statement's original block to allow statement sinking of a |
| statement. Larger numbers result in more aggressive statement sinking. |
| The default value is 75. A small positive adjustment is applied for |
| statements with memory operands as those are even more profitable so sink. |
| |
| @item max-stores-to-sink |
| The maximum number of conditional stores paires that can be sunk. Set to 0 |
| if either vectorization (@option{-ftree-vectorize}) or if-conversion |
| (@option{-ftree-loop-if-convert}) is disabled. The default is 2. |
| |
| @item allow-load-data-races |
| Allow optimizers to introduce new data races on loads. |
| Set to 1 to allow, otherwise to 0. This option is enabled by default |
| unless implicitly set by the @option{-fmemory-model=} option. |
| |
| @item allow-store-data-races |
| Allow optimizers to introduce new data races on stores. |
| Set to 1 to allow, otherwise to 0. This option is enabled by default |
| unless implicitly set by the @option{-fmemory-model=} option. |
| |
| @item allow-packed-load-data-races |
| Allow optimizers to introduce new data races on packed data loads. |
| Set to 1 to allow, otherwise to 0. This option is enabled by default |
| unless implicitly set by the @option{-fmemory-model=} option. |
| |
| @item allow-packed-store-data-races |
| Allow optimizers to introduce new data races on packed data stores. |
| Set to 1 to allow, otherwise to 0. This option is enabled by default |
| unless implicitly set by the @option{-fmemory-model=} option. |
| |
| @item case-values-threshold |
| The smallest number of different values for which it is best to use a |
| jump-table instead of a tree of conditional branches. If the value is |
| 0, use the default for the machine. The default is 0. |
| |
| @item tree-reassoc-width |
| Set the maximum number of instructions executed in parallel in |
| reassociated tree. This parameter overrides target dependent |
| heuristics used by default if has non zero value. |
| |
| @item sched-pressure-algorithm |
| Choose between the two available implementations of |
| @option{-fsched-pressure}. Algorithm 1 is the original implementation |
| and is the more likely to prevent instructions from being reordered. |
| Algorithm 2 was designed to be a compromise between the relatively |
| conservative approach taken by algorithm 1 and the rather aggressive |
| approach taken by the default scheduler. It relies more heavily on |
| having a regular register file and accurate register pressure classes. |
| See @file{haifa-sched.c} in the GCC sources for more details. |
| |
| The default choice depends on the target. |
| |
| @item max-slsr-cand-scan |
| Set the maximum number of existing candidates that will be considered when |
| seeking a basis for a new straight-line strength reduction candidate. |
| |
| @end table |
| @end table |
| |
| @node Preprocessor Options |
| @section Options Controlling the Preprocessor |
| @cindex preprocessor options |
| @cindex options, preprocessor |
| |
| These options control the C preprocessor, which is run on each C source |
| file before actual compilation. |
| |
| If you use the @option{-E} option, nothing is done except preprocessing. |
| Some of these options make sense only together with @option{-E} because |
| they cause the preprocessor output to be unsuitable for actual |
| compilation. |
| |
| @table @gcctabopt |
| @item -Wp,@var{option} |
| @opindex Wp |
| You can use @option{-Wp,@var{option}} to bypass the compiler driver |
| and pass @var{option} directly through to the preprocessor. If |
| @var{option} contains commas, it is split into multiple options at the |
| commas. However, many options are modified, translated or interpreted |
| by the compiler driver before being passed to the preprocessor, and |
| @option{-Wp} forcibly bypasses this phase. The preprocessor's direct |
| interface is undocumented and subject to change, so whenever possible |
| you should avoid using @option{-Wp} and let the driver handle the |
| options instead. |
| |
| @item -Xpreprocessor @var{option} |
| @opindex Xpreprocessor |
| Pass @var{option} as an option to the preprocessor. You can use this to |
| supply system-specific preprocessor options that GCC does not |
| recognize. |
| |
| If you want to pass an option that takes an argument, you must use |
| @option{-Xpreprocessor} twice, once for the option and once for the argument. |
| |
| @item -no-integrated-cpp |
| @opindex no-integrated-cpp |
| Perform preprocessing as a separate pass before compilation. |
| By default, GCC performs preprocessing as an integrated part of |
| input tokenization and parsing. |
| If this option is provided, the appropriate language front end |
| (@command{cc1}, @command{cc1plus}, or @command{cc1obj} for C, C++, |
| and Objective-C, respectively) is instead invoked twice, |
| once for preprocessing only and once for actual compilation |
| of the preprocessed input. |
| This option may be useful in conjunction with the @option{-B} or |
| @option{-wrapper} options to specify an alternate preprocessor or |
| perform additional processing of the program source between |
| normal preprocessing and compilation. |
| @end table |
| |
| @include cppopts.texi |
| |
| @node Assembler Options |
| @section Passing Options to the Assembler |
| |
| @c prevent bad page break with this line |
| You can pass options to the assembler. |
| |
| @table @gcctabopt |
| @item -Wa,@var{option} |
| @opindex Wa |
| Pass @var{option} as an option to the assembler. If @var{option} |
| contains commas, it is split into multiple options at the commas. |
| |
| @item -Xassembler @var{option} |
| @opindex Xassembler |
| Pass @var{option} as an option to the assembler. You can use this to |
| supply system-specific assembler options that GCC does not |
| recognize. |
| |
| If you want to pass an option that takes an argument, you must use |
| @option{-Xassembler} twice, once for the option and once for the argument. |
| |
| @end table |
| |
| @node Link Options |
| @section Options for Linking |
| @cindex link options |
| @cindex options, linking |
| |
| These options come into play when the compiler links object files into |
| an executable output file. They are meaningless if the compiler is |
| not doing a link step. |
| |
| @table @gcctabopt |
| @cindex file names |
| @item @var{object-file-name} |
| A file name that does not end in a special recognized suffix is |
| considered to name an object file or library. (Object files are |
| distinguished from libraries by the linker according to the file |
| contents.) If linking is done, these object files are used as input |
| to the linker. |
| |
| @item -c |
| @itemx -S |
| @itemx -E |
| @opindex c |
| @opindex S |
| @opindex E |
| If any of these options is used, then the linker is not run, and |
| object file names should not be used as arguments. @xref{Overall |
| Options}. |
| |
| @cindex Libraries |
| @item -l@var{library} |
| @itemx -l @var{library} |
| @opindex l |
| Search the library named @var{library} when linking. (The second |
| alternative with the library as a separate argument is only for |
| POSIX compliance and is not recommended.) |
| |
| It makes a difference where in the command you write this option; the |
| linker searches and processes libraries and object files in the order they |
| are specified. Thus, @samp{foo.o -lz bar.o} searches library @samp{z} |
| after file @file{foo.o} but before @file{bar.o}. If @file{bar.o} refers |
| to functions in @samp{z}, those functions may not be loaded. |
| |
| The linker searches a standard list of directories for the library, |
| which is actually a file named @file{lib@var{library}.a}. The linker |
| then uses this file as if it had been specified precisely by name. |
| |
| The directories searched include several standard system directories |
| plus any that you specify with @option{-L}. |
| |
| Normally the files found this way are library files---archive files |
| whose members are object files. The linker handles an archive file by |
| scanning through it for members which define symbols that have so far |
| been referenced but not defined. But if the file that is found is an |
| ordinary object file, it is linked in the usual fashion. The only |
| difference between using an @option{-l} option and specifying a file name |
| is that @option{-l} surrounds @var{library} with @samp{lib} and @samp{.a} |
| and searches several directories. |
| |
| @item -lobjc |
| @opindex lobjc |
| You need this special case of the @option{-l} option in order to |
| link an Objective-C or Objective-C++ program. |
| |
| @item -nostartfiles |
| @opindex nostartfiles |
| Do not use the standard system startup files when linking. |
| The standard system libraries are used normally, unless @option{-nostdlib} |
| or @option{-nodefaultlibs} is used. |
| |
| @item -nodefaultlibs |
| @opindex nodefaultlibs |
| Do not use the standard system libraries when linking. |
| Only the libraries you specify are passed to the linker, and options |
| specifying linkage of the system libraries, such as @code{-static-libgcc} |
| or @code{-shared-libgcc}, are ignored. |
| The standard startup files are used normally, unless @option{-nostartfiles} |
| is used. |
| |
| The compiler may generate calls to @code{memcmp}, |
| @code{memset}, @code{memcpy} and @code{memmove}. |
| These entries are usually resolved by entries in |
| libc. These entry points should be supplied through some other |
| mechanism when this option is specified. |
| |
| @item -nostdlib |
| @opindex nostdlib |
| Do not use the standard system startup files or libraries when linking. |
| No startup files and only the libraries you specify are passed to |
| the linker, and options specifying linkage of the system libraries, such as |
| @code{-static-libgcc} or @code{-shared-libgcc}, are ignored. |
| |
| The compiler may generate calls to @code{memcmp}, @code{memset}, |
| @code{memcpy} and @code{memmove}. |
| These entries are usually resolved by entries in |
| libc. These entry points should be supplied through some other |
| mechanism when this option is specified. |
| |
| @cindex @option{-lgcc}, use with @option{-nostdlib} |
| @cindex @option{-nostdlib} and unresolved references |
| @cindex unresolved references and @option{-nostdlib} |
| @cindex @option{-lgcc}, use with @option{-nodefaultlibs} |
| @cindex @option{-nodefaultlibs} and unresolved references |
| @cindex unresolved references and @option{-nodefaultlibs} |
| One of the standard libraries bypassed by @option{-nostdlib} and |
| @option{-nodefaultlibs} is @file{libgcc.a}, a library of internal subroutines |
| which GCC uses to overcome shortcomings of particular machines, or special |
| needs for some languages. |
| (@xref{Interface,,Interfacing to GCC Output,gccint,GNU Compiler |
| Collection (GCC) Internals}, |
| for more discussion of @file{libgcc.a}.) |
| In most cases, you need @file{libgcc.a} even when you want to avoid |
| other standard libraries. In other words, when you specify @option{-nostdlib} |
| or @option{-nodefaultlibs} you should usually specify @option{-lgcc} as well. |
| This ensures that you have no unresolved references to internal GCC |
| library subroutines. |
| (An example of such an internal subroutine is @samp{__main}, used to ensure C++ |
| constructors are called; @pxref{Collect2,,@code{collect2}, gccint, |
| GNU Compiler Collection (GCC) Internals}.) |
| |
| @item -pie |
| @opindex pie |
| Produce a position independent executable on targets that support it. |
| For predictable results, you must also specify the same set of options |
| used for compilation (@option{-fpie}, @option{-fPIE}, |
| or model suboptions) when you specify this linker option. |
| |
| @item -rdynamic |
| @opindex rdynamic |
| Pass the flag @option{-export-dynamic} to the ELF linker, on targets |
| that support it. This instructs the linker to add all symbols, not |
| only used ones, to the dynamic symbol table. This option is needed |
| for some uses of @code{dlopen} or to allow obtaining backtraces |
| from within a program. |
| |
| @item -s |
| @opindex s |
| Remove all symbol table and relocation information from the executable. |
| |
| @item -static |
| @opindex static |
| On systems that support dynamic linking, this prevents linking with the shared |
| libraries. On other systems, this option has no effect. |
| |
| @item -shared |
| @opindex shared |
| Produce a shared object which can then be linked with other objects to |
| form an executable. Not all systems support this option. For predictable |
| results, you must also specify the same set of options used for compilation |
| (@option{-fpic}, @option{-fPIC}, or model suboptions) when |
| you specify this linker option.@footnote{On some systems, @samp{gcc -shared} |
| needs to build supplementary stub code for constructors to work. On |
| multi-libbed systems, @samp{gcc -shared} must select the correct support |
| libraries to link against. Failing to supply the correct flags may lead |
| to subtle defects. Supplying them in cases where they are not necessary |
| is innocuous.} |
| |
| @item -shared-libgcc |
| @itemx -static-libgcc |
| @opindex shared-libgcc |
| @opindex static-libgcc |
| On systems that provide @file{libgcc} as a shared library, these options |
| force the use of either the shared or static version, respectively. |
| If no shared version of @file{libgcc} was built when the compiler was |
| configured, these options have no effect. |
| |
| There are several situations in which an application should use the |
| shared @file{libgcc} instead of the static version. The most common |
| of these is when the application wishes to throw and catch exceptions |
| across different shared libraries. In that case, each of the libraries |
| as well as the application itself should use the shared @file{libgcc}. |
| |
| Therefore, the G++ and GCJ drivers automatically add |
| @option{-shared-libgcc} whenever you build a shared library or a main |
| executable, because C++ and Java programs typically use exceptions, so |
| this is the right thing to do. |
| |
| If, instead, you use the GCC driver to create shared libraries, you may |
| find that they are not always linked with the shared @file{libgcc}. |
| If GCC finds, at its configuration time, that you have a non-GNU linker |
| or a GNU linker that does not support option @option{--eh-frame-hdr}, |
| it links the shared version of @file{libgcc} into shared libraries |
| by default. Otherwise, it takes advantage of the linker and optimizes |
| away the linking with the shared version of @file{libgcc}, linking with |
| the static version of libgcc by default. This allows exceptions to |
| propagate through such shared libraries, without incurring relocation |
| costs at library load time. |
| |
| However, if a library or main executable is supposed to throw or catch |
| exceptions, you must link it using the G++ or GCJ driver, as appropriate |
| for the languages used in the program, or using the option |
| @option{-shared-libgcc}, such that it is linked with the shared |
| @file{libgcc}. |
| |
| @item -static-libstdc++ |
| When the @command{g++} program is used to link a C++ program, it |
| normally automatically links against @option{libstdc++}. If |
| @file{libstdc++} is available as a shared library, and the |
| @option{-static} option is not used, then this links against the |
| shared version of @file{libstdc++}. That is normally fine. However, it |
| is sometimes useful to freeze the version of @file{libstdc++} used by |
| the program without going all the way to a fully static link. The |
| @option{-static-libstdc++} option directs the @command{g++} driver to |
| link @file{libstdc++} statically, without necessarily linking other |
| libraries statically. |
| |
| @item -symbolic |
| @opindex symbolic |
| Bind references to global symbols when building a shared object. Warn |
| about any unresolved references (unless overridden by the link editor |
| option @option{-Xlinker -z -Xlinker defs}). Only a few systems support |
| this option. |
| |
| @item -T @var{script} |
| @opindex T |
| @cindex linker script |
| Use @var{script} as the linker script. This option is supported by most |
| systems using the GNU linker. On some targets, such as bare-board |
| targets without an operating system, the @option{-T} option may be required |
| when linking to avoid references to undefined symbols. |
| |
| @item -Xlinker @var{option} |
| @opindex Xlinker |
| Pass @var{option} as an option to the linker. You can use this to |
| supply system-specific linker options that GCC does not recognize. |
| |
| If you want to pass an option that takes a separate argument, you must use |
| @option{-Xlinker} twice, once for the option and once for the argument. |
| For example, to pass @option{-assert definitions}, you must write |
| @option{-Xlinker -assert -Xlinker definitions}. It does not work to write |
| @option{-Xlinker "-assert definitions"}, because this passes the entire |
| string as a single argument, which is not what the linker expects. |
| |
| When using the GNU linker, it is usually more convenient to pass |
| arguments to linker options using the @option{@var{option}=@var{value}} |
| syntax than as separate arguments. For example, you can specify |
| @option{-Xlinker -Map=output.map} rather than |
| @option{-Xlinker -Map -Xlinker output.map}. Other linkers may not support |
| this syntax for command-line options. |
| |
| @item -Wl,@var{option} |
| @opindex Wl |
| Pass @var{option} as an option to the linker. If @var{option} contains |
| commas, it is split into multiple options at the commas. You can use this |
| syntax to pass an argument to the option. |
| For example, @option{-Wl,-Map,output.map} passes @option{-Map output.map} to the |
| linker. When using the GNU linker, you can also get the same effect with |
| @option{-Wl,-Map=output.map}. |
| |
| @item -u @var{symbol} |
| @opindex u |
| Pretend the symbol @var{symbol} is undefined, to force linking of |
| library modules to define it. You can use @option{-u} multiple times with |
| different symbols to force loading of additional library modules. |
| @end table |
| |
| @node Directory Options |
| @section Options for Directory Search |
| @cindex directory options |
| @cindex options, directory search |
| @cindex search path |
| |
| These options specify directories to search for header files, for |
| libraries and for parts of the compiler: |
| |
| @table @gcctabopt |
| @item -I@var{dir} |
| @opindex I |
| Add the directory @var{dir} to the head of the list of directories to be |
| searched for header files. This can be used to override a system header |
| file, substituting your own version, since these directories are |
| searched before the system header file directories. However, you should |
| not use this option to add directories that contain vendor-supplied |
| system header files (use @option{-isystem} for that). If you use more than |
| one @option{-I} option, the directories are scanned in left-to-right |
| order; the standard system directories come after. |
| |
| If a standard system include directory, or a directory specified with |
| @option{-isystem}, is also specified with @option{-I}, the @option{-I} |
| option is ignored. The directory is still searched but as a |
| system directory at its normal position in the system include chain. |
| This is to ensure that GCC's procedure to fix buggy system headers and |
| the ordering for the @code{include_next} directive are not inadvertently changed. |
| If you really need to change the search order for system directories, |
| use the @option{-nostdinc} and/or @option{-isystem} options. |
| |
| @item -iplugindir=@var{dir} |
| Set the directory to search for plugins that are passed |
| by @option{-fplugin=@var{name}} instead of |
| @option{-fplugin=@var{path}/@var{name}.so}. This option is not meant |
| to be used by the user, but only passed by the driver. |
| |
| @item -iquote@var{dir} |
| @opindex iquote |
| Add the directory @var{dir} to the head of the list of directories to |
| be searched for header files only for the case of @samp{#include |
| "@var{file}"}; they are not searched for @samp{#include <@var{file}>}, |
| otherwise just like @option{-I}. |
| |
| @item -L@var{dir} |
| @opindex L |
| Add directory @var{dir} to the list of directories to be searched |
| for @option{-l}. |
| |
| @item -B@var{prefix} |
| @opindex B |
| This option specifies where to find the executables, libraries, |
| include files, and data files of the compiler itself. |
| |
| The compiler driver program runs one or more of the subprograms |
| @command{cpp}, @command{cc1}, @command{as} and @command{ld}. It tries |
| @var{prefix} as a prefix for each program it tries to run, both with and |
| without @samp{@var{machine}/@var{version}/} (@pxref{Target Options}). |
| |
| For each subprogram to be run, the compiler driver first tries the |
| @option{-B} prefix, if any. If that name is not found, or if @option{-B} |
| is not specified, the driver tries two standard prefixes, |
| @file{/usr/lib/gcc/} and @file{/usr/local/lib/gcc/}. If neither of |
| those results in a file name that is found, the unmodified program |
| name is searched for using the directories specified in your |
| @env{PATH} environment variable. |
| |
| The compiler checks to see if the path provided by the @option{-B} |
| refers to a directory, and if necessary it adds a directory |
| separator character at the end of the path. |
| |
| @option{-B} prefixes that effectively specify directory names also apply |
| to libraries in the linker, because the compiler translates these |
| options into @option{-L} options for the linker. They also apply to |
| includes files in the preprocessor, because the compiler translates these |
| options into @option{-isystem} options for the preprocessor. In this case, |
| the compiler appends @samp{include} to the prefix. |
| |
| The runtime support file @file{libgcc.a} can also be searched for using |
| the @option{-B} prefix, if needed. If it is not found there, the two |
| standard prefixes above are tried, and that is all. The file is left |
| out of the link if it is not found by those means. |
| |
| Another way to specify a prefix much like the @option{-B} prefix is to use |
| the environment variable @env{GCC_EXEC_PREFIX}. @xref{Environment |
| Variables}. |
| |
| As a special kludge, if the path provided by @option{-B} is |
| @file{[dir/]stage@var{N}/}, where @var{N} is a number in the range 0 to |
| 9, then it is replaced by @file{[dir/]include}. This is to help |
| with boot-strapping the compiler. |
| |
| @item -specs=@var{file} |
| @opindex specs |
| Process @var{file} after the compiler reads in the standard @file{specs} |
| file, in order to override the defaults which the @command{gcc} driver |
| program uses when determining what switches to pass to @command{cc1}, |
| @command{cc1plus}, @command{as}, @command{ld}, etc. More than one |
| @option{-specs=@var{file}} can be specified on the command line, and they |
| are processed in order, from left to right. |
| |
| @item --sysroot=@var{dir} |
| @opindex sysroot |
| Use @var{dir} as the logical root directory for headers and libraries. |
| For example, if the compiler normally searches for headers in |
| @file{/usr/include} and libraries in @file{/usr/lib}, it instead |
| searches @file{@var{dir}/usr/include} and @file{@var{dir}/usr/lib}. |
| |
| If you use both this option and the @option{-isysroot} option, then |
| the @option{--sysroot} option applies to libraries, but the |
| @option{-isysroot} option applies to header files. |
| |
| The GNU linker (beginning with version 2.16) has the necessary support |
| for this option. If your linker does not support this option, the |
| header file aspect of @option{--sysroot} still works, but the |
| library aspect does not. |
| |
| @item --no-sysroot-suffix |
| @opindex no-sysroot-suffix |
| For some targets, a suffix is added to the root directory specified |
| with @option{--sysroot}, depending on the other options used, so that |
| headers may for example be found in |
| @file{@var{dir}/@var{suffix}/usr/include} instead of |
| @file{@var{dir}/usr/include}. This option disables the addition of |
| such a suffix. |
| |
| @item -I- |
| @opindex I- |
| This option has been deprecated. Please use @option{-iquote} instead for |
| @option{-I} directories before the @option{-I-} and remove the @option{-I-}. |
| Any directories you specify with @option{-I} options before the @option{-I-} |
| option are searched only for the case of @samp{#include "@var{file}"}; |
| they are not searched for @samp{#include <@var{file}>}. |
| |
| If additional directories are specified with @option{-I} options after |
| the @option{-I-}, these directories are searched for all @samp{#include} |
| directives. (Ordinarily @emph{all} @option{-I} directories are used |
| this way.) |
| |
| In addition, the @option{-I-} option inhibits the use of the current |
| directory (where the current input file came from) as the first search |
| directory for @samp{#include "@var{file}"}. There is no way to |
| override this effect of @option{-I-}. With @option{-I.} you can specify |
| searching the directory that is current when the compiler is |
| invoked. That is not exactly the same as what the preprocessor does |
| by default, but it is often satisfactory. |
| |
| @option{-I-} does not inhibit the use of the standard system directories |
| for header files. Thus, @option{-I-} and @option{-nostdinc} are |
| independent. |
| @end table |
| |
| @c man end |
| |
| @node Spec Files |
| @section Specifying subprocesses and the switches to pass to them |
| @cindex Spec Files |
| |
| @command{gcc} is a driver program. It performs its job by invoking a |
| sequence of other programs to do the work of compiling, assembling and |
| linking. GCC interprets its command-line parameters and uses these to |
| deduce which programs it should invoke, and which command-line options |
| it ought to place on their command lines. This behavior is controlled |
| by @dfn{spec strings}. In most cases there is one spec string for each |
| program that GCC can invoke, but a few programs have multiple spec |
| strings to control their behavior. The spec strings built into GCC can |
| be overridden by using the @option{-specs=} command-line switch to specify |
| a spec file. |
| |
| @dfn{Spec files} are plaintext files that are used to construct spec |
| strings. They consist of a sequence of directives separated by blank |
| lines. The type of directive is determined by the first non-whitespace |
| character on the line, which can be one of the following: |
| |
| @table @code |
| @item %@var{command} |
| Issues a @var{command} to the spec file processor. The commands that can |
| appear here are: |
| |
| @table @code |
| @item %include <@var{file}> |
| @cindex @code{%include} |
| Search for @var{file} and insert its text at the current point in the |
| specs file. |
| |
| @item %include_noerr <@var{file}> |
| @cindex @code{%include_noerr} |
| Just like @samp{%include}, but do not generate an error message if the include |
| file cannot be found. |
| |
| @item %rename @var{old_name} @var{new_name} |
| @cindex @code{%rename} |
| Rename the spec string @var{old_name} to @var{new_name}. |
| |
| @end table |
| |
| @item *[@var{spec_name}]: |
| This tells the compiler to create, override or delete the named spec |
| string. All lines after this directive up to the next directive or |
| blank line are considered to be the text for the spec string. If this |
| results in an empty string then the spec is deleted. (Or, if the |
| spec did not exist, then nothing happens.) Otherwise, if the spec |
| does not currently exist a new spec is created. If the spec does |
| exist then its contents are overridden by the text of this |
| directive, unless the first character of that text is the @samp{+} |
| character, in which case the text is appended to the spec. |
| |
| @item [@var{suffix}]: |
| Creates a new @samp{[@var{suffix}] spec} pair. All lines after this directive |
| and up to the next directive or blank line are considered to make up the |
| spec string for the indicated suffix. When the compiler encounters an |
| input file with the named suffix, it processes the spec string in |
| order to work out how to compile that file. For example: |
| |
| @smallexample |
| .ZZ: |
| z-compile -input %i |
| @end smallexample |
| |
| This says that any input file whose name ends in @samp{.ZZ} should be |
| passed to the program @samp{z-compile}, which should be invoked with the |
| command-line switch @option{-input} and with the result of performing the |
| @samp{%i} substitution. (See below.) |
| |
| As an alternative to providing a spec string, the text following a |
| suffix directive can be one of the following: |
| |
| @table @code |
| @item @@@var{language} |
| This says that the suffix is an alias for a known @var{language}. This is |
| similar to using the @option{-x} command-line switch to GCC to specify a |
| language explicitly. For example: |
| |
| @smallexample |
| .ZZ: |
| @@c++ |
| @end smallexample |
| |
| Says that .ZZ files are, in fact, C++ source files. |
| |
| @item #@var{name} |
| This causes an error messages saying: |
| |
| @smallexample |
| @var{name} compiler not installed on this system. |
| @end smallexample |
| @end table |
| |
| GCC already has an extensive list of suffixes built into it. |
| This directive adds an entry to the end of the list of suffixes, but |
| since the list is searched from the end backwards, it is effectively |
| possible to override earlier entries using this technique. |
| |
| @end table |
| |
| GCC has the following spec strings built into it. Spec files can |
| override these strings or create their own. Note that individual |
| targets can also add their own spec strings to this list. |
| |
| @smallexample |
| asm Options to pass to the assembler |
| asm_final Options to pass to the assembler post-processor |
| cpp Options to pass to the C preprocessor |
| cc1 Options to pass to the C compiler |
| cc1plus Options to pass to the C++ compiler |
| endfile Object files to include at the end of the link |
| link Options to pass to the linker |
| lib Libraries to include on the command line to the linker |
| libgcc Decides which GCC support library to pass to the linker |
| linker Sets the name of the linker |
| predefines Defines to be passed to the C preprocessor |
| signed_char Defines to pass to CPP to say whether @code{char} is signed |
| by default |
| startfile Object files to include at the start of the link |
| @end smallexample |
| |
| Here is a small example of a spec file: |
| |
| @smallexample |
| %rename lib old_lib |
| |
| *lib: |
| --start-group -lgcc -lc -leval1 --end-group %(old_lib) |
| @end smallexample |
| |
| This example renames the spec called @samp{lib} to @samp{old_lib} and |
| then overrides the previous definition of @samp{lib} with a new one. |
| The new definition adds in some extra command-line options before |
| including the text of the old definition. |
| |
| @dfn{Spec strings} are a list of command-line options to be passed to their |
| corresponding program. In addition, the spec strings can contain |
| @samp{%}-prefixed sequences to substitute variable text or to |
| conditionally insert text into the command line. Using these constructs |
| it is possible to generate quite complex command lines. |
| |
| Here is a table of all defined @samp{%}-sequences for spec |
| strings. Note that spaces are not generated automatically around the |
| results of expanding these sequences. Therefore you can concatenate them |
| together or combine them with constant text in a single argument. |
| |
| @table @code |
| @item %% |
| Substitute one @samp{%} into the program name or argument. |
| |
| @item %i |
| Substitute the name of the input file being processed. |
| |
| @item %b |
| Substitute the basename of the input file being processed. |
| This is the substring up to (and not including) the last period |
| and not including the directory. |
| |
| @item %B |
| This is the same as @samp{%b}, but include the file suffix (text after |
| the last period). |
| |
| @item %d |
| Marks the argument containing or following the @samp{%d} as a |
| temporary file name, so that that file is deleted if GCC exits |
| successfully. Unlike @samp{%g}, this contributes no text to the |
| argument. |
| |
| @item %g@var{suffix} |
| Substitute a file name that has suffix @var{suffix} and is chosen |
| once per compilation, and mark the argument in the same way as |
| @samp{%d}. To reduce exposure to denial-of-service attacks, the file |
| name is now chosen in a way that is hard to predict even when previously |
| chosen file names are known. For example, @samp{%g.s @dots{} %g.o @dots{} %g.s} |
| might turn into @samp{ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s}. @var{suffix} matches |
| the regexp @samp{[.A-Za-z]*} or the special string @samp{%O}, which is |
| treated exactly as if @samp{%O} had been preprocessed. Previously, @samp{%g} |
| was simply substituted with a file name chosen once per compilation, |
| without regard to any appended suffix (which was therefore treated |
| just like ordinary text), making such attacks more likely to succeed. |
| |
| @item %u@var{suffix} |
| Like @samp{%g}, but generates a new temporary file name |
| each time it appears instead of once per compilation. |
| |
| @item %U@var{suffix} |
| Substitutes the last file name generated with @samp{%u@var{suffix}}, generating a |
| new one if there is no such last file name. In the absence of any |
| @samp{%u@var{suffix}}, this is just like @samp{%g@var{suffix}}, except they don't share |
| the same suffix @emph{space}, so @samp{%g.s @dots{} %U.s @dots{} %g.s @dots{} %U.s} |
| involves the generation of two distinct file names, one |
| for each @samp{%g.s} and another for each @samp{%U.s}. Previously, @samp{%U} was |
| simply substituted with a file name chosen for the previous @samp{%u}, |
| without regard to any appended suffix. |
| |
| @item %j@var{suffix} |
| Substitutes the name of the @code{HOST_BIT_BUCKET}, if any, and if it is |
| writable, and if @option{-save-temps} is not used; |
| otherwise, substitute the name |
| of a temporary file, just like @samp{%u}. This temporary file is not |
| meant for communication between processes, but rather as a junk |
| disposal mechanism. |
| |
| @item %|@var{suffix} |
| @itemx %m@var{suffix} |
| Like @samp{%g}, except if @option{-pipe} is in effect. In that case |
| @samp{%|} substitutes a single dash and @samp{%m} substitutes nothing at |
| all. These are the two most common ways to instruct a program that it |
| should read from standard input or write to standard output. If you |
| need something more elaborate you can use an @samp{%@{pipe:@code{X}@}} |
| construct: see for example @file{f/lang-specs.h}. |
| |
| @item %.@var{SUFFIX} |
| Substitutes @var{.SUFFIX} for the suffixes of a matched switch's args |
| when it is subsequently output with @samp{%*}. @var{SUFFIX} is |
| terminated by the next space or %. |
| |
| @item %w |
| Marks the argument containing or following the @samp{%w} as the |
| designated output file of this compilation. This puts the argument |
| into the sequence of arguments that @samp{%o} substitutes. |
| |
| @item %o |
| Substitutes the names of all the output files, with spaces |
| automatically placed around them. You should write spaces |
| around the @samp{%o} as well or the results are undefined. |
| @samp{%o} is for use in the specs for running the linker. |
| Input files whose names have no recognized suffix are not compiled |
| at all, but they are included among the output files, so they are |
| linked. |
| |
| @item %O |
| Substitutes the suffix for object files. Note that this is |
| handled specially when it immediately follows @samp{%g, %u, or %U}, |
| because of the need for those to form complete file names. The |
| handling is such that @samp{%O} is treated exactly as if it had already |
| been substituted, except that @samp{%g, %u, and %U} do not currently |
| support additional @var{suffix} characters following @samp{%O} as they do |
| following, for example, @samp{.o}. |
| |
| @item %p |
| Substitutes the standard macro predefinitions for the |
| current target machine. Use this when running @code{cpp}. |
| |
| @item %P |
| Like @samp{%p}, but puts @samp{__} before and after the name of each |
| predefined macro, except for macros that start with @samp{__} or with |
| @samp{_@var{L}}, where @var{L} is an uppercase letter. This is for ISO |
| C@. |
| |
| @item %I |
| Substitute any of @option{-iprefix} (made from @env{GCC_EXEC_PREFIX}), |
| @option{-isysroot} (made from @env{TARGET_SYSTEM_ROOT}), |
| @option{-isystem} (made from @env{COMPILER_PATH} and @option{-B} options) |
| and @option{-imultilib} as necessary. |
| |
| @item %s |
| Current argument is the name of a library or startup file of some sort. |
| Search for that file in a standard list of directories and substitute |
| the full name found. The current working directory is included in the |
| list of directories scanned. |
| |
| @item %T |
| Current argument is the name of a linker script. Search for that file |
| in the current list of directories to scan for libraries. If the file |
| is located insert a @option{--script} option into the command line |
| followed by the full path name found. If the file is not found then |
| generate an error message. Note: the current working directory is not |
| searched. |
| |
| @item %e@var{str} |
| Print @var{str} as an error message. @var{str} is terminated by a newline. |
| Use this when inconsistent options are detected. |
| |
| @item %(@var{name}) |
| Substitute the contents of spec string @var{name} at this point. |
| |
| @item %x@{@var{option}@} |
| Accumulate an option for @samp{%X}. |
| |
| @item %X |
| Output the accumulated linker options specified by @option{-Wl} or a @samp{%x} |
| spec string. |
| |
| @item %Y |
| Output the accumulated assembler options specified by @option{-Wa}. |
| |
| @item %Z |
| Output the accumulated preprocessor options specified by @option{-Wp}. |
| |
| @item %a |
| Process the @code{asm} spec. This is used to compute the |
| switches to be passed to the assembler. |
| |
| @item %A |
| Process the @code{asm_final} spec. This is a spec string for |
| passing switches to an assembler post-processor, if such a program is |
| needed. |
| |
| @item %l |
| Process the @code{link} spec. This is the spec for computing the |
| command line passed to the linker. Typically it makes use of the |
| @samp{%L %G %S %D and %E} sequences. |
| |
| @item %D |
| Dump out a @option{-L} option for each directory that GCC believes might |
| contain startup files. If the target supports multilibs then the |
| current multilib directory is prepended to each of these paths. |
| |
| @item %L |
| Process the @code{lib} spec. This is a spec string for deciding which |
| libraries are included on the command line to the linker. |
| |
| @item %G |
| Process the @code{libgcc} spec. This is a spec string for deciding |
| which GCC support library is included on the command line to the linker. |
| |
| @item %S |
| Process the @code{startfile} spec. This is a spec for deciding which |
| object files are the first ones passed to the linker. Typically |
| this might be a file named @file{crt0.o}. |
| |
| @item %E |
| Process the @code{endfile} spec. This is a spec string that specifies |
| the last object files that are passed to the linker. |
| |
| @item %C |
| Process the @code{cpp} spec. This is used to construct the arguments |
| to be passed to the C preprocessor. |
| |
| @item %1 |
| Process the @code{cc1} spec. This is used to construct the options to be |
| passed to the actual C compiler (@samp{cc1}). |
| |
| @item %2 |
| Process the @code{cc1plus} spec. This is used to construct the options to be |
| passed to the actual C++ compiler (@samp{cc1plus}). |
| |
| @item %* |
| Substitute the variable part of a matched option. See below. |
| Note that each comma in the substituted string is replaced by |
| a single space. |
| |
| @item %<@code{S} |
| Remove all occurrences of @code{-S} from the command line. Note---this |
| command is position dependent. @samp{%} commands in the spec string |
| before this one see @code{-S}, @samp{%} commands in the spec string |
| after this one do not. |
| |
| @item %:@var{function}(@var{args}) |
| Call the named function @var{function}, passing it @var{args}. |
| @var{args} is first processed as a nested spec string, then split |
| into an argument vector in the usual fashion. The function returns |
| a string which is processed as if it had appeared literally as part |
| of the current spec. |
| |
| The following built-in spec functions are provided: |
| |
| @table @code |
| @item @code{getenv} |
| The @code{getenv} spec function takes two arguments: an environment |
| variable name and a string. If the environment variable is not |
| defined, a fatal error is issued. Otherwise, the return value is the |
| value of the environment variable concatenated with the string. For |
| example, if @env{TOPDIR} is defined as @file{/path/to/top}, then: |
| |
| @smallexample |
| %:getenv(TOPDIR /include) |
| @end smallexample |
| |
| expands to @file{/path/to/top/include}. |
| |
| @item @code{if-exists} |
| The @code{if-exists} spec function takes one argument, an absolute |
| pathname to a file. If the file exists, @code{if-exists} returns the |
| pathname. Here is a small example of its usage: |
| |
| @smallexample |
| *startfile: |
| crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s |
| @end smallexample |
| |
| @item @code{if-exists-else} |
| The @code{if-exists-else} spec function is similar to the @code{if-exists} |
| spec function, except that it takes two arguments. The first argument is |
| an absolute pathname to a file. If the file exists, @code{if-exists-else} |
| returns the pathname. If it does not exist, it returns the second argument. |
| This way, @code{if-exists-else} can be used to select one file or another, |
| based on the existence of the first. Here is a small example of its usage: |
| |
| @smallexample |
| *startfile: |
| crt0%O%s %:if-exists(crti%O%s) \ |
| %:if-exists-else(crtbeginT%O%s crtbegin%O%s) |
| @end smallexample |
| |
| @item @code{replace-outfile} |
| The @code{replace-outfile} spec function takes two arguments. It looks for the |
| first argument in the outfiles array and replaces it with the second argument. Here |
| is a small example of its usage: |
| |
| @smallexample |
| %@{fgnu-runtime:%:replace-outfile(-lobjc -lobjc-gnu)@} |
| @end smallexample |
| |
| @item @code{remove-outfile} |
| The @code{remove-outfile} spec function takes one argument. It looks for the |
| first argument in the outfiles array and removes it. Here is a small example |
| its usage: |
| |
| @smallexample |
| %:remove-outfile(-lm) |
| @end smallexample |
| |
| @item @code{pass-through-libs} |
| The @code{pass-through-libs} spec function takes any number of arguments. It |
| finds any @option{-l} options and any non-options ending in @file{.a} (which it |
| assumes are the names of linker input library archive files) and returns a |
| result containing all the found arguments each prepended by |
| @option{-plugin-opt=-pass-through=} and joined by spaces. This list is |
| intended to be passed to the LTO linker plugin. |
| |
| @smallexample |
| %:pass-through-libs(%G %L %G) |
| @end smallexample |
| |
| @item @code{print-asm-header} |
| The @code{print-asm-header} function takes no arguments and simply |
| prints a banner like: |
| |
| @smallexample |
| Assembler options |
| ================= |
| |
| Use "-Wa,OPTION" to pass "OPTION" to the assembler. |
| @end smallexample |
| |
| It is used to separate compiler options from assembler options |
| in the @option{--target-help} output. |
| @end table |
| |
| @item %@{@code{S}@} |
| Substitutes the @code{-S} switch, if that switch is given to GCC@. |
| If that switch is not specified, this substitutes nothing. Note that |
| the leading dash is omitted when specifying this option, and it is |
| automatically inserted if the substitution is performed. Thus the spec |
| string @samp{%@{foo@}} matches the command-line option @option{-foo} |
| and outputs the command-line option @option{-foo}. |
| |
| @item %W@{@code{S}@} |
| Like %@{@code{S}@} but mark last argument supplied within as a file to be |
| deleted on failure. |
| |
| @item %@{@code{S}*@} |
| Substitutes all the switches specified to GCC whose names start |
| with @code{-S}, but which also take an argument. This is used for |
| switches like @option{-o}, @option{-D}, @option{-I}, etc. |
| GCC considers @option{-o foo} as being |
| one switch whose name starts with @samp{o}. %@{o*@} substitutes this |
| text, including the space. Thus two arguments are generated. |
| |
| @item %@{@code{S}*&@code{T}*@} |
| Like %@{@code{S}*@}, but preserve order of @code{S} and @code{T} options |
| (the order of @code{S} and @code{T} in the spec is not significant). |
| There can be any number of ampersand-separated variables; for each the |
| wild card is optional. Useful for CPP as @samp{%@{D*&U*&A*@}}. |
| |
| @item %@{@code{S}:@code{X}@} |
| Substitutes @code{X}, if the @option{-S} switch is given to GCC@. |
| |
| @item %@{!@code{S}:@code{X}@} |
| Substitutes @code{X}, if the @option{-S} switch is @emph{not} given to GCC@. |
| |
| @item %@{@code{S}*:@code{X}@} |
| Substitutes @code{X} if one or more switches whose names start with |
| @code{-S} are specified to GCC@. Normally @code{X} is substituted only |
| once, no matter how many such switches appeared. However, if @code{%*} |
| appears somewhere in @code{X}, then @code{X} is substituted once |
| for each matching switch, with the @code{%*} replaced by the part of |
| that switch matching the @code{*}. |
| |
| @item %@{.@code{S}:@code{X}@} |
| Substitutes @code{X}, if processing a file with suffix @code{S}. |
| |
| @item %@{!.@code{S}:@code{X}@} |
| Substitutes @code{X}, if @emph{not} processing a file with suffix @code{S}. |
| |
| @item %@{,@code{S}:@code{X}@} |
| Substitutes @code{X}, if processing a file for language @code{S}. |
| |
| @item %@{!,@code{S}:@code{X}@} |
| Substitutes @code{X}, if not processing a file for language @code{S}. |
| |
| @item %@{@code{S}|@code{P}:@code{X}@} |
| Substitutes @code{X} if either @code{-S} or @code{-P} is given to |
| GCC@. This may be combined with @samp{!}, @samp{.}, @samp{,}, and |
| @code{*} sequences as well, although they have a stronger binding than |
| the @samp{|}. If @code{%*} appears in @code{X}, all of the |
| alternatives must be starred, and only the first matching alternative |
| is substituted. |
| |
| For example, a spec string like this: |
| |
| @smallexample |
| %@{.c:-foo@} %@{!.c:-bar@} %@{.c|d:-baz@} %@{!.c|d:-boggle@} |
| @end smallexample |
| |
| @noindent |
| outputs the following command-line options from the following input |
| command-line options: |
| |
| @smallexample |
| fred.c -foo -baz |
| jim.d -bar -boggle |
| -d fred.c -foo -baz -boggle |
| -d jim.d -bar -baz -boggle |
| @end smallexample |
| |
| @item %@{S:X; T:Y; :D@} |
| |
| If @code{S} is given to GCC, substitutes @code{X}; else if @code{T} is |
| given to GCC, substitutes @code{Y}; else substitutes @code{D}. There can |
| be as many clauses as you need. This may be combined with @code{.}, |
| @code{,}, @code{!}, @code{|}, and @code{*} as needed. |
| |
| |
| @end table |
| |
| The conditional text @code{X} in a %@{@code{S}:@code{X}@} or similar |
| construct may contain other nested @samp{%} constructs or spaces, or |
| even newlines. They are processed as usual, as described above. |
| Trailing white space in @code{X} is ignored. White space may also |
| appear anywhere on the left side of the colon in these constructs, |
| except between @code{.} or @code{*} and the corresponding word. |
| |
| The @option{-O}, @option{-f}, @option{-m}, and @option{-W} switches are |
| handled specifically in these constructs. If another value of |
| @option{-O} or the negated form of a @option{-f}, @option{-m}, or |
| @option{-W} switch is found later in the command line, the earlier |
| switch value is ignored, except with @{@code{S}*@} where @code{S} is |
| just one letter, which passes all matching options. |
| |
| The character @samp{|} at the beginning of the predicate text is used to |
| indicate that a command should be piped to the following command, but |
| only if @option{-pipe} is specified. |
| |
| It is built into GCC which switches take arguments and which do not. |
| (You might think it would be useful to generalize this to allow each |
| compiler's spec to say which switches take arguments. But this cannot |
| be done in a consistent fashion. GCC cannot even decide which input |
| files have been specified without knowing which switches take arguments, |
| and it must know which input files to compile in order to tell which |
| compilers to run). |
| |
| GCC also knows implicitly that arguments starting in @option{-l} are to be |
| treated as compiler output files, and passed to the linker in their |
| proper position among the other output files. |
| |
| @c man begin OPTIONS |
| |
| @node Target Options |
| @section Specifying Target Machine and Compiler Version |
| @cindex target options |
| @cindex cross compiling |
| @cindex specifying machine version |
| @cindex specifying compiler version and target machine |
| @cindex compiler version, specifying |
| @cindex target machine, specifying |
| |
| The usual way to run GCC is to run the executable called @command{gcc}, or |
| @command{@var{machine}-gcc} when cross-compiling, or |
| @command{@var{machine}-gcc-@var{version}} to run a version other than the |
| one that was installed last. |
| |
| @node Submodel Options |
| @section Hardware Models and Configurations |
| @cindex submodel options |
| @cindex specifying hardware config |
| @cindex hardware models and configurations, specifying |
| @cindex machine dependent options |
| |
| Each target machine types can have its own |
| special options, starting with @samp{-m}, to choose among various |
| hardware models or configurations---for example, 68010 vs 68020, |
| floating coprocessor or none. A single installed version of the |
| compiler can compile for any model or configuration, according to the |
| options specified. |
| |
| Some configurations of the compiler also support additional special |
| options, usually for compatibility with other compilers on the same |
| platform. |
| |
| @c This list is ordered alphanumerically by subsection name. |
| @c It should be the same order and spelling as these options are listed |
| @c in Machine Dependent Options |
| |
| @menu |
| * AArch64 Options:: |
| * Adapteva Epiphany Options:: |
| * ARM Options:: |
| * AVR Options:: |
| * Blackfin Options:: |
| * C6X Options:: |
| * CRIS Options:: |
| * CR16 Options:: |
| * Darwin Options:: |
| * DEC Alpha Options:: |
| * FR30 Options:: |
| * FRV Options:: |
| * GNU/Linux Options:: |
| * H8/300 Options:: |
| * HPPA Options:: |
| * i386 and x86-64 Options:: |
| * i386 and x86-64 Windows Options:: |
| * IA-64 Options:: |
| * LM32 Options:: |
| * M32C Options:: |
| * M32R/D Options:: |
| * M680x0 Options:: |
| * MCore Options:: |
| * MeP Options:: |
| * MicroBlaze Options:: |
| * MIPS Options:: |
| * MMIX Options:: |
| * MN10300 Options:: |
| * Moxie Options:: |
| * PDP-11 Options:: |
| * picoChip Options:: |
| * PowerPC Options:: |
| * RL78 Options:: |
| * RS/6000 and PowerPC Options:: |
| * RX Options:: |
| * S/390 and zSeries Options:: |
| * Score Options:: |
| * SH Options:: |
| * Solaris 2 Options:: |
| * SPARC Options:: |
| * SPU Options:: |
| * System V Options:: |
| * TILE-Gx Options:: |
| * TILEPro Options:: |
| * V850 Options:: |
| * VAX Options:: |
| * VMS Options:: |
| * VxWorks Options:: |
| * x86-64 Options:: |
| * Xstormy16 Options:: |
| * Xtensa Options:: |
| * zSeries Options:: |
| @end menu |
| |
| @node Adapteva Epiphany Options |
| @subsection Adapteva Epiphany Options |
| |
| These @samp{-m} options are defined for Adapteva Epiphany: |
| |
| @table @gcctabopt |
| @item -mhalf-reg-file |
| @opindex mhalf-reg-file |
| Don't allocate any register in the range @code{r32}@dots{}@code{r63}. |
| That allows code to run on hardware variants that lack these registers. |
| |
| @item -mprefer-short-insn-regs |
| @opindex mprefer-short-insn-regs |
| Preferrentially allocate registers that allow short instruction generation. |
| This can result in increased instruction count, so this may either reduce or |
| increase overall code size. |
| |
| @item -mbranch-cost=@var{num} |
| @opindex mbranch-cost |
| Set the cost of branches to roughly @var{num} ``simple'' instructions. |
| This cost is only a heuristic and is not guaranteed to produce |
| consistent results across releases. |
| |
| @item -mcmove |
| @opindex mcmove |
| Enable the generation of conditional moves. |
| |
| @item -mnops=@var{num} |
| @opindex mnops |
| Emit @var{num} NOPs before every other generated instruction. |
| |
| @item -mno-soft-cmpsf |
| @opindex mno-soft-cmpsf |
| For single-precision floating-point comparisons, emit an @code{fsub} instruction |
| and test the flags. This is faster than a software comparison, but can |
| get incorrect results in the presence of NaNs, or when two different small |
| numbers are compared such that their difference is calculated as zero. |
| The default is @option{-msoft-cmpsf}, which uses slower, but IEEE-compliant, |
| software comparisons. |
| |
| @item -mstack-offset=@var{num} |
| @opindex mstack-offset |
| Set the offset between the top of the stack and the stack pointer. |
| E.g., a value of 8 means that the eight bytes in the range @code{sp+0@dots{}sp+7} |
| can be used by leaf functions without stack allocation. |
| Values other than @samp{8} or @samp{16} are untested and unlikely to work. |
| Note also that this option changes the ABI; compiling a program with a |
| different stack offset than the libraries have been compiled with |
| generally does not work. |
| This option can be useful if you want to evaluate if a different stack |
| offset would give you better code, but to actually use a different stack |
| offset to build working programs, it is recommended to configure the |
| toolchain with the appropriate @option{--with-stack-offset=@var{num}} option. |
| |
| @item -mno-round-nearest |
| @opindex mno-round-nearest |
| Make the scheduler assume that the rounding mode has been set to |
| truncating. The default is @option{-mround-nearest}. |
| |
| @item -mlong-calls |
| @opindex mlong-calls |
| If not otherwise specified by an attribute, assume all calls might be beyond |
| the offset range of the @code{b} / @code{bl} instructions, and therefore load the |
| function address into a register before performing a (otherwise direct) call. |
| This is the default. |
| |
| @item -mshort-calls |
| @opindex short-calls |
| If not otherwise specified by an attribute, assume all direct calls are |
| in the range of the @code{b} / @code{bl} instructions, so use these instructions |
| for direct calls. The default is @option{-mlong-calls}. |
| |
| @item -msmall16 |
| @opindex msmall16 |
| Assume addresses can be loaded as 16-bit unsigned values. This does not |
| apply to function addresses for which @option{-mlong-calls} semantics |
| are in effect. |
| |
| @item -mfp-mode=@var{mode} |
| @opindex mfp-mode |
| Set the prevailing mode of the floating-point unit. |
| This determines the floating-point mode that is provided and expected |
| at function call and return time. Making this mode match the mode you |
| predominantly need at function start can make your programs smaller and |
| faster by avoiding unnecessary mode switches. |
| |
| @var{mode} can be set to one the following values: |
| |
| @table @samp |
| @item caller |
| Any mode at function entry is valid, and retained or restored when |
| the function returns, and when it calls other functions. |
| This mode is useful for compiling libraries or other compilation units |
| you might want to incorporate into different programs with different |
| prevailing FPU modes, and the convenience of being able to use a single |
| object file outweighs the size and speed overhead for any extra |
| mode switching that might be needed, compared with what would be needed |
| with a more specific choice of prevailing FPU mode. |
| |
| @item truncate |
| This is the mode used for floating-point calculations with |
| truncating (i.e.@: round towards zero) rounding mode. That includes |
| conversion from floating point to integer. |
| |
| @item round-nearest |
| This is the mode used for floating-point calculations with |
| round-to-nearest-or-even rounding mode. |
| |
| @item int |
| This is the mode used to perform integer calculations in the FPU, e.g.@: |
| integer multiply, or integer multiply-and-accumulate. |
| @end table |
| |
| The default is @option{-mfp-mode=caller} |
| |
| @item -mnosplit-lohi |
| @opindex mnosplit-lohi |
| @item -mno-postinc |
| @opindex mno-postinc |
| @item -mno-postmodify |
| @opindex mno-postmodify |
| Code generation tweaks that disable, respectively, splitting of 32-bit |
| loads, generation of post-increment addresses, and generation of |
| post-modify addresses. The defaults are @option{msplit-lohi}, |
| @option{-mpost-inc}, and @option{-mpost-modify}. |
| |
| @item -mnovect-double |
| @opindex mno-vect-double |
| Change the preferred SIMD mode to SImode. The default is |
| @option{-mvect-double}, which uses DImode as preferred SIMD mode. |
| |
| @item -max-vect-align=@var{num} |
| @opindex max-vect-align |
| The maximum alignment for SIMD vector mode types. |
| @var{num} may be 4 or 8. The default is 8. |
| Note that this is an ABI change, even though many library function |
| interfaces are unaffected if they don't use SIMD vector modes |
| in places that affect size and/or alignment of relevant types. |
| |
| @item -msplit-vecmove-early |
| @opindex msplit-vecmove-early |
| Split vector moves into single word moves before reload. In theory this |
| can give better register allocation, but so far the reverse seems to be |
| generally the case. |
| |
| @item -m1reg-@var{reg} |
| @opindex m1reg- |
| Specify a register to hold the constant @minus{}1, which makes loading small negative |
| constants and certain bitmasks faster. |
| Allowable values for @var{reg} are @samp{r43} and @samp{r63}, |
| which specify use of that register as a fixed register, |
| and @samp{none}, which means that no register is used for this |
| purpose. The default is @option{-m1reg-none}. |
| |
| @end table |
| |
| @node AArch64 Options |
| @subsection AArch64 Options |
| @cindex AArch64 Options |
| |
| These options are defined for AArch64 implementations: |
| |
| @table @gcctabopt |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate big-endian code. This is the default when GCC is configured for an |
| @samp{aarch64_be-*-*} target. |
| |
| @item -mgeneral-regs-only |
| @opindex mgeneral-regs-only |
| Generate code which uses only the general registers. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate little-endian code. This is the default when GCC is configured for an |
| @samp{aarch64-*-*} but not an @samp{aarch64_be-*-*} target. |
| |
| @item -mcmodel=tiny |
| @opindex mcmodel=tiny |
| Generate code for the tiny code model. The program and its statically defined |
| symbols must be within 1GB of each other. Pointers are 64 bits. Programs can |
| be statically or dynamically linked. This model is not fully implemented and |
| mostly treated as "small". |
| |
| @item -mcmodel=small |
| @opindex mcmodel=small |
| Generate code for the small code model. The program and its statically defined |
| symbols must be within 4GB of each other. Pointers are 64 bits. Programs can |
| be statically or dynamically linked. This is the default code model. |
| |
| @item -mcmodel=large |
| @opindex mcmodel=large |
| Generate code for the large code model. This makes no assumptions about |
| addresses and sizes of sections. Pointers are 64 bits. Programs can be |
| statically linked only. |
| |
| @item -mstrict-align |
| @opindex mstrict-align |
| Do not assume that unaligned memory references will be handled by the system. |
| |
| @item -momit-leaf-frame-pointer |
| @item -mno-omit-leaf-frame-pointer |
| @opindex momit-leaf-frame-pointer |
| @opindex mno-omit-leaf-frame-pointer |
| Omit or keep the frame pointer in leaf functions. The former behaviour is the |
| default. |
| |
| @item -mtls-dialect=desc |
| @opindex mtls-dialect=desc |
| Use TLS descriptors as the thread-local storage mechanism for dynamic accesses |
| of TLS variables. This is the default. |
| |
| @item -mtls-dialect=traditional |
| @opindex mtls-dialect=traditional |
| Use traditional TLS as the thread-local storage mechanism for dynamic accesses |
| of TLS variables. |
| |
| @item -march=@var{name} |
| @opindex march |
| Specify the name of the target architecture, optionally suffixed by one or |
| more feature modifiers. This option has the form |
| @option{-march=@var{arch}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the |
| only value for @var{arch} is @samp{armv8-a}. The possible values for |
| @var{feature} are documented in the sub-section below. |
| |
| Where conflicting feature modifiers are specified, the right-most feature is |
| used. |
| |
| GCC uses this name to determine what kind of instructions it can emit when |
| generating assembly code. This option can be used in conjunction with or |
| instead of the @option{-mcpu=} option. |
| |
| @item -mcpu=@var{name} |
| @opindex mcpu |
| Specify the name of the target processor, optionally suffixed by one or more |
| feature modifiers. This option has the form |
| @option{-mcpu=@var{cpu}@r{@{}+@r{[}no@r{]}@var{feature}@r{@}*}}, where the |
| possible values for @var{cpu} are @samp{generic}, @samp{large}. The |
| possible values for @var{feature} are documented in the sub-section |
| below. |
| |
| Where conflicting feature modifiers are specified, the right-most feature is |
| used. |
| |
| GCC uses this name to determine what kind of instructions it can emit when |
| generating assembly code. |
| |
| @item -mtune=@var{name} |
| @opindex mtune |
| Specify the name of the processor to tune the performance for. The code will |
| be tuned as if the target processor were of the type specified in this option, |
| but still using instructions compatible with the target processor specified |
| by a @option{-mcpu=} option. This option cannot be suffixed by feature |
| modifiers. |
| |
| @end table |
| |
| @subsubsection @option{-march} and @option{-mcpu} feature modifiers |
| @cindex @option{-march} feature modifiers |
| @cindex @option{-mcpu} feature modifiers |
| Feature modifiers used with @option{-march} and @option{-mcpu} can be one |
| the following: |
| |
| @table @samp |
| @item crypto |
| Enable Crypto extension. This implies Advanced SIMD is enabled. |
| @item fp |
| Enable floating-point instructions. |
| @item simd |
| Enable Advanced SIMD instructions. This implies floating-point instructions |
| are enabled. This is the default for all current possible values for options |
| @option{-march} and @option{-mcpu=}. |
| @end table |
| |
| @node ARM Options |
| @subsection ARM Options |
| @cindex ARM options |
| |
| These @samp{-m} options are defined for Advanced RISC Machines (ARM) |
| architectures: |
| |
| @table @gcctabopt |
| @item -mabi=@var{name} |
| @opindex mabi |
| Generate code for the specified ABI@. Permissible values are: @samp{apcs-gnu}, |
| @samp{atpcs}, @samp{aapcs}, @samp{aapcs-linux} and @samp{iwmmxt}. |
| |
| @item -mapcs-frame |
| @opindex mapcs-frame |
| Generate a stack frame that is compliant with the ARM Procedure Call |
| Standard for all functions, even if this is not strictly necessary for |
| correct execution of the code. Specifying @option{-fomit-frame-pointer} |
| with this option causes the stack frames not to be generated for |
| leaf functions. The default is @option{-mno-apcs-frame}. |
| |
| @item -mapcs |
| @opindex mapcs |
| This is a synonym for @option{-mapcs-frame}. |
| |
| @ignore |
| @c not currently implemented |
| @item -mapcs-stack-check |
| @opindex mapcs-stack-check |
| Generate code to check the amount of stack space available upon entry to |
| every function (that actually uses some stack space). If there is |
| insufficient space available then either the function |
| @samp{__rt_stkovf_split_small} or @samp{__rt_stkovf_split_big} is |
| called, depending upon the amount of stack space required. The runtime |
| system is required to provide these functions. The default is |
| @option{-mno-apcs-stack-check}, since this produces smaller code. |
| |
| @c not currently implemented |
| @item -mapcs-float |
| @opindex mapcs-float |
| Pass floating-point arguments using the floating-point registers. This is |
| one of the variants of the APCS@. This option is recommended if the |
| target hardware has a floating-point unit or if a lot of floating-point |
| arithmetic is going to be performed by the code. The default is |
| @option{-mno-apcs-float}, since the size of integer-only code is |
| slightly increased if @option{-mapcs-float} is used. |
| |
| @c not currently implemented |
| @item -mapcs-reentrant |
| @opindex mapcs-reentrant |
| Generate reentrant, position-independent code. The default is |
| @option{-mno-apcs-reentrant}. |
| @end ignore |
| |
| @item -mthumb-interwork |
| @opindex mthumb-interwork |
| Generate code that supports calling between the ARM and Thumb |
| instruction sets. Without this option, on pre-v5 architectures, the |
| two instruction sets cannot be reliably used inside one program. The |
| default is @option{-mno-thumb-interwork}, since slightly larger code |
| is generated when @option{-mthumb-interwork} is specified. In AAPCS |
| configurations this option is meaningless. |
| |
| @item -mno-sched-prolog |
| @opindex mno-sched-prolog |
| Prevent the reordering of instructions in the function prologue, or the |
| merging of those instruction with the instructions in the function's |
| body. This means that all functions start with a recognizable set |
| of instructions (or in fact one of a choice from a small set of |
| different function prologues), and this information can be used to |
| locate the start of functions inside an executable piece of code. The |
| default is @option{-msched-prolog}. |
| |
| @item -mfloat-abi=@var{name} |
| @opindex mfloat-abi |
| Specifies which floating-point ABI to use. Permissible values |
| are: @samp{soft}, @samp{softfp} and @samp{hard}. |
| |
| Specifying @samp{soft} causes GCC to generate output containing |
| library calls for floating-point operations. |
| @samp{softfp} allows the generation of code using hardware floating-point |
| instructions, but still uses the soft-float calling conventions. |
| @samp{hard} allows generation of floating-point instructions |
| and uses FPU-specific calling conventions. |
| |
| The default depends on the specific target configuration. Note that |
| the hard-float and soft-float ABIs are not link-compatible; you must |
| compile your entire program with the same ABI, and link with a |
| compatible set of libraries. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate code for a processor running in little-endian mode. This is |
| the default for all standard configurations. |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate code for a processor running in big-endian mode; the default is |
| to compile code for a little-endian processor. |
| |
| @item -mwords-little-endian |
| @opindex mwords-little-endian |
| This option only applies when generating code for big-endian processors. |
| Generate code for a little-endian word order but a big-endian byte |
| order. That is, a byte order of the form @samp{32107654}. Note: this |
| option should only be used if you require compatibility with code for |
| big-endian ARM processors generated by versions of the compiler prior to |
| 2.8. This option is now deprecated. |
| |
| @item -mcpu=@var{name} |
| @opindex mcpu |
| This specifies the name of the target ARM processor. GCC uses this name |
| to determine what kind of instructions it can emit when generating |
| assembly code. Permissible names are: @samp{arm2}, @samp{arm250}, |
| @samp{arm3}, @samp{arm6}, @samp{arm60}, @samp{arm600}, @samp{arm610}, |
| @samp{arm620}, @samp{arm7}, @samp{arm7m}, @samp{arm7d}, @samp{arm7dm}, |
| @samp{arm7di}, @samp{arm7dmi}, @samp{arm70}, @samp{arm700}, |
| @samp{arm700i}, @samp{arm710}, @samp{arm710c}, @samp{arm7100}, |
| @samp{arm720}, |
| @samp{arm7500}, @samp{arm7500fe}, @samp{arm7tdmi}, @samp{arm7tdmi-s}, |
| @samp{arm710t}, @samp{arm720t}, @samp{arm740t}, |
| @samp{strongarm}, @samp{strongarm110}, @samp{strongarm1100}, |
| @samp{strongarm1110}, |
| @samp{arm8}, @samp{arm810}, @samp{arm9}, @samp{arm9e}, @samp{arm920}, |
| @samp{arm920t}, @samp{arm922t}, @samp{arm946e-s}, @samp{arm966e-s}, |
| @samp{arm968e-s}, @samp{arm926ej-s}, @samp{arm940t}, @samp{arm9tdmi}, |
| @samp{arm10tdmi}, @samp{arm1020t}, @samp{arm1026ej-s}, |
| @samp{arm10e}, @samp{arm1020e}, @samp{arm1022e}, |
| @samp{arm1136j-s}, @samp{arm1136jf-s}, @samp{mpcore}, @samp{mpcorenovfp}, |
| @samp{arm1156t2-s}, @samp{arm1156t2f-s}, @samp{arm1176jz-s}, @samp{arm1176jzf-s}, |
| @samp{cortex-a5}, @samp{cortex-a7}, @samp{cortex-a8}, @samp{cortex-a9}, |
| @samp{cortex-a15}, @samp{cortex-r4}, @samp{cortex-r4f}, @samp{cortex-r5}, |
| @samp{cortex-m4}, @samp{cortex-m3}, |
| @samp{cortex-m1}, |
| @samp{cortex-m0}, |
| @samp{cortex-m0plus}, |
| @samp{xscale}, @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}, |
| @samp{fa526}, @samp{fa626}, |
| @samp{fa606te}, @samp{fa626te}, @samp{fmp626}, @samp{fa726te}. |
| |
| |
| @option{-mcpu=generic-@var{arch}} is also permissible, and is |
| equivalent to @option{-march=@var{arch} -mtune=generic-@var{arch}}. |
| See @option{-mtune} for more information. |
| |
| @option{-mcpu=native} causes the compiler to auto-detect the CPU |
| of the build computer. At present, this feature is only supported on |
| Linux, and not all architectures are recognized. If the auto-detect is |
| unsuccessful the option has no effect. |
| |
| @item -mtune=@var{name} |
| @opindex mtune |
| This option is very similar to the @option{-mcpu=} option, except that |
| instead of specifying the actual target processor type, and hence |
| restricting which instructions can be used, it specifies that GCC should |
| tune the performance of the code as if the target were of the type |
| specified in this option, but still choosing the instructions it |
| generates based on the CPU specified by a @option{-mcpu=} option. |
| For some ARM implementations better performance can be obtained by using |
| this option. |
| |
| @option{-mtune=generic-@var{arch}} specifies that GCC should tune the |
| performance for a blend of processors within architecture @var{arch}. |
| The aim is to generate code that run well on the current most popular |
| processors, balancing between optimizations that benefit some CPUs in the |
| range, and avoiding performance pitfalls of other CPUs. The effects of |
| this option may change in future GCC versions as CPU models come and go. |
| |
| @option{-mtune=native} causes the compiler to auto-detect the CPU |
| of the build computer. At present, this feature is only supported on |
| Linux, and not all architectures are recognized. If the auto-detect is |
| unsuccessful the option has no effect. |
| |
| @item -march=@var{name} |
| @opindex march |
| This specifies the name of the target ARM architecture. GCC uses this |
| name to determine what kind of instructions it can emit when generating |
| assembly code. This option can be used in conjunction with or instead |
| of the @option{-mcpu=} option. Permissible names are: @samp{armv2}, |
| @samp{armv2a}, @samp{armv3}, @samp{armv3m}, @samp{armv4}, @samp{armv4t}, |
| @samp{armv5}, @samp{armv5t}, @samp{armv5e}, @samp{armv5te}, |
| @samp{armv6}, @samp{armv6j}, |
| @samp{armv6t2}, @samp{armv6z}, @samp{armv6zk}, @samp{armv6-m}, |
| @samp{armv7}, @samp{armv7-a}, @samp{armv7-r}, @samp{armv7-m}, |
| @samp{iwmmxt}, @samp{iwmmxt2}, @samp{ep9312}. |
| |
| @option{-march=native} causes the compiler to auto-detect the architecture |
| of the build computer. At present, this feature is only supported on |
| Linux, and not all architectures are recognized. If the auto-detect is |
| unsuccessful the option has no effect. |
| |
| @item -mfpu=@var{name} |
| @opindex mfpu |
| This specifies what floating-point hardware (or hardware emulation) is |
| available on the target. Permissible names are: @samp{vfp}, @samp{vfpv3}, |
| @samp{vfpv3-fp16}, @samp{vfpv3-d16}, @samp{vfpv3-d16-fp16}, @samp{vfpv3xd}, |
| @samp{vfpv3xd-fp16}, @samp{neon}, @samp{neon-fp16}, @samp{vfpv4}, |
| @samp{vfpv4-d16}, @samp{fpv4-sp-d16} and @samp{neon-vfpv4}. |
| |
| If @option{-msoft-float} is specified this specifies the format of |
| floating-point values. |
| |
| If the selected floating-point hardware includes the NEON extension |
| (e.g. @option{-mfpu}=@samp{neon}), note that floating-point |
| operations are not generated by GCC's auto-vectorization pass unless |
| @option{-funsafe-math-optimizations} is also specified. This is |
| because NEON hardware does not fully implement the IEEE 754 standard for |
| floating-point arithmetic (in particular denormal values are treated as |
| zero), so the use of NEON instructions may lead to a loss of precision. |
| |
| @item -mfp16-format=@var{name} |
| @opindex mfp16-format |
| Specify the format of the @code{__fp16} half-precision floating-point type. |
| Permissible names are @samp{none}, @samp{ieee}, and @samp{alternative}; |
| the default is @samp{none}, in which case the @code{__fp16} type is not |
| defined. @xref{Half-Precision}, for more information. |
| |
| @item -mstructure-size-boundary=@var{n} |
| @opindex mstructure-size-boundary |
| The sizes of all structures and unions are rounded up to a multiple |
| of the number of bits set by this option. Permissible values are 8, 32 |
| and 64. The default value varies for different toolchains. For the COFF |
| targeted toolchain the default value is 8. A value of 64 is only allowed |
| if the underlying ABI supports it. |
| |
| Specifying a larger number can produce faster, more efficient code, but |
| can also increase the size of the program. Different values are potentially |
| incompatible. Code compiled with one value cannot necessarily expect to |
| work with code or libraries compiled with another value, if they exchange |
| information using structures or unions. |
| |
| @item -mabort-on-noreturn |
| @opindex mabort-on-noreturn |
| Generate a call to the function @code{abort} at the end of a |
| @code{noreturn} function. It is executed if the function tries to |
| return. |
| |
| @item -mlong-calls |
| @itemx -mno-long-calls |
| @opindex mlong-calls |
| @opindex mno-long-calls |
| Tells the compiler to perform function calls by first loading the |
| address of the function into a register and then performing a subroutine |
| call on this register. This switch is needed if the target function |
| lies outside of the 64-megabyte addressing range of the offset-based |
| version of subroutine call instruction. |
| |
| Even if this switch is enabled, not all function calls are turned |
| into long calls. The heuristic is that static functions, functions |
| that have the @samp{short-call} attribute, functions that are inside |
| the scope of a @samp{#pragma no_long_calls} directive, and functions whose |
| definitions have already been compiled within the current compilation |
| unit are not turned into long calls. The exceptions to this rule are |
| that weak function definitions, functions with the @samp{long-call} |
| attribute or the @samp{section} attribute, and functions that are within |
| the scope of a @samp{#pragma long_calls} directive are always |
| turned into long calls. |
| |
| This feature is not enabled by default. Specifying |
| @option{-mno-long-calls} restores the default behavior, as does |
| placing the function calls within the scope of a @samp{#pragma |
| long_calls_off} directive. Note these switches have no effect on how |
| the compiler generates code to handle function calls via function |
| pointers. |
| |
| @item -msingle-pic-base |
| @opindex msingle-pic-base |
| Treat the register used for PIC addressing as read-only, rather than |
| loading it in the prologue for each function. The runtime system is |
| responsible for initializing this register with an appropriate value |
| before execution begins. |
| |
| @item -mpic-register=@var{reg} |
| @opindex mpic-register |
| Specify the register to be used for PIC addressing. The default is R10 |
| unless stack-checking is enabled, when R9 is used. |
| |
| @item -mcirrus-fix-invalid-insns |
| @opindex mcirrus-fix-invalid-insns |
| @opindex mno-cirrus-fix-invalid-insns |
| Insert NOPs into the instruction stream to in order to work around |
| problems with invalid Maverick instruction combinations. This option |
| is only valid if the @option{-mcpu=ep9312} option has been used to |
| enable generation of instructions for the Cirrus Maverick floating-point |
| co-processor. This option is not enabled by default, since the |
| problem is only present in older Maverick implementations. The default |
| can be re-enabled by use of the @option{-mno-cirrus-fix-invalid-insns} |
| switch. |
| |
| @item -mpoke-function-name |
| @opindex mpoke-function-name |
| Write the name of each function into the text section, directly |
| preceding the function prologue. The generated code is similar to this: |
| |
| @smallexample |
| t0 |
| .ascii "arm_poke_function_name", 0 |
| .align |
| t1 |
| .word 0xff000000 + (t1 - t0) |
| arm_poke_function_name |
| mov ip, sp |
| stmfd sp!, @{fp, ip, lr, pc@} |
| sub fp, ip, #4 |
| @end smallexample |
| |
| When performing a stack backtrace, code can inspect the value of |
| @code{pc} stored at @code{fp + 0}. If the trace function then looks at |
| location @code{pc - 12} and the top 8 bits are set, then we know that |
| there is a function name embedded immediately preceding this location |
| and has length @code{((pc[-3]) & 0xff000000)}. |
| |
| @item -mthumb |
| @itemx -marm |
| @opindex marm |
| @opindex mthumb |
| |
| Select between generating code that executes in ARM and Thumb |
| states. The default for most configurations is to generate code |
| that executes in ARM state, but the default can be changed by |
| configuring GCC with the @option{--with-mode=}@var{state} |
| configure option. |
| |
| @item -mtpcs-frame |
| @opindex mtpcs-frame |
| Generate a stack frame that is compliant with the Thumb Procedure Call |
| Standard for all non-leaf functions. (A leaf function is one that does |
| not call any other functions.) The default is @option{-mno-tpcs-frame}. |
| |
| @item -mtpcs-leaf-frame |
| @opindex mtpcs-leaf-frame |
| Generate a stack frame that is compliant with the Thumb Procedure Call |
| Standard for all leaf functions. (A leaf function is one that does |
| not call any other functions.) The default is @option{-mno-apcs-leaf-frame}. |
| |
| @item -mcallee-super-interworking |
| @opindex mcallee-super-interworking |
| Gives all externally visible functions in the file being compiled an ARM |
| instruction set header which switches to Thumb mode before executing the |
| rest of the function. This allows these functions to be called from |
| non-interworking code. This option is not valid in AAPCS configurations |
| because interworking is enabled by default. |
| |
| @item -mcaller-super-interworking |
| @opindex mcaller-super-interworking |
| Allows calls via function pointers (including virtual functions) to |
| execute correctly regardless of whether the target code has been |
| compiled for interworking or not. There is a small overhead in the cost |
| of executing a function pointer if this option is enabled. This option |
| is not valid in AAPCS configurations because interworking is enabled |
| by default. |
| |
| @item -mtp=@var{name} |
| @opindex mtp |
| Specify the access model for the thread local storage pointer. The valid |
| models are @option{soft}, which generates calls to @code{__aeabi_read_tp}, |
| @option{cp15}, which fetches the thread pointer from @code{cp15} directly |
| (supported in the arm6k architecture), and @option{auto}, which uses the |
| best available method for the selected processor. The default setting is |
| @option{auto}. |
| |
| @item -mtls-dialect=@var{dialect} |
| @opindex mtls-dialect |
| Specify the dialect to use for accessing thread local storage. Two |
| @var{dialect}s are supported---@samp{gnu} and @samp{gnu2}. The |
| @samp{gnu} dialect selects the original GNU scheme for supporting |
| local and global dynamic TLS models. The @samp{gnu2} dialect |
| selects the GNU descriptor scheme, which provides better performance |
| for shared libraries. The GNU descriptor scheme is compatible with |
| the original scheme, but does require new assembler, linker and |
| library support. Initial and local exec TLS models are unaffected by |
| this option and always use the original scheme. |
| |
| @item -mword-relocations |
| @opindex mword-relocations |
| Only generate absolute relocations on word-sized values (i.e. R_ARM_ABS32). |
| This is enabled by default on targets (uClinux, SymbianOS) where the runtime |
| loader imposes this restriction, and when @option{-fpic} or @option{-fPIC} |
| is specified. |
| |
| @item -mfix-cortex-m3-ldrd |
| @opindex mfix-cortex-m3-ldrd |
| Some Cortex-M3 cores can cause data corruption when @code{ldrd} instructions |
| with overlapping destination and base registers are used. This option avoids |
| generating these instructions. This option is enabled by default when |
| @option{-mcpu=cortex-m3} is specified. |
| |
| @item -munaligned-access |
| @itemx -mno-unaligned-access |
| @opindex munaligned-access |
| @opindex mno-unaligned-access |
| Enables (or disables) reading and writing of 16- and 32- bit values |
| from addresses that are not 16- or 32- bit aligned. By default |
| unaligned access is disabled for all pre-ARMv6 and all ARMv6-M |
| architectures, and enabled for all other architectures. If unaligned |
| access is not enabled then words in packed data structures will be |
| accessed a byte at a time. |
| |
| The ARM attribute @code{Tag_CPU_unaligned_access} will be set in the |
| generated object file to either true or false, depending upon the |
| setting of this option. If unaligned access is enabled then the |
| preprocessor symbol @code{__ARM_FEATURE_UNALIGNED} will also be |
| defined. |
| |
| @end table |
| |
| @node AVR Options |
| @subsection AVR Options |
| @cindex AVR Options |
| |
| These options are defined for AVR implementations: |
| |
| @table @gcctabopt |
| @item -mmcu=@var{mcu} |
| @opindex mmcu |
| Specify Atmel AVR instruction set architectures (ISA) or MCU type. |
| |
| For a complete list of @var{mcu} values that are supported by @command{avr-gcc}, |
| see the compiler output when called with the @option{--help=target} |
| command line option. |
| The default for this option is@tie{}@code{avr2}. |
| |
| GCC supports the following AVR devices and ISAs: |
| |
| @include avr-mmcu.texi |
| |
| @item -maccumulate-args |
| @opindex maccumulate-args |
| Accumulate outgoing function arguments and acquire/release the needed |
| stack space for outgoing function arguments once in function |
| prologue/epilogue. Without this option, outgoing arguments are pushed |
| before calling a function and popped afterwards. |
| |
| Popping the arguments after the function call can be expensive on |
| AVR so that accumulating the stack space might lead to smaller |
| executables because arguments need not to be removed from the |
| stack after such a function call. |
| |
| This option can lead to reduced code size for functions that perform |
| several calls to functions that get their arguments on the stack like |
| calls to printf-like functions. |
| |
| @item -mbranch-cost=@var{cost} |
| @opindex mbranch-cost |
| Set the branch costs for conditional branch instructions to |
| @var{cost}. Reasonable values for @var{cost} are small, non-negative |
| integers. The default branch cost is 0. |
| |
| @item -mcall-prologues |
| @opindex mcall-prologues |
| Functions prologues/epilogues are expanded as calls to appropriate |
| subroutines. Code size is smaller. |
| |
| @item -mint8 |
| @opindex mint8 |
| Assume @code{int} to be 8-bit integer. This affects the sizes of all types: a |
| @code{char} is 1 byte, an @code{int} is 1 byte, a @code{long} is 2 bytes, |
| and @code{long long} is 4 bytes. Please note that this option does not |
| conform to the C standards, but it results in smaller code |
| size. |
| |
| @item -mno-interrupts |
| @opindex mno-interrupts |
| Generated code is not compatible with hardware interrupts. |
| Code size is smaller. |
| |
| @item -mrelax |
| @opindex mrelax |
| Try to replace @code{CALL} resp.@: @code{JMP} instruction by the shorter |
| @code{RCALL} resp.@: @code{RJMP} instruction if applicable. |
| Setting @code{-mrelax} just adds the @code{--relax} option to the |
| linker command line when the linker is called. |
| |
| Jump relaxing is performed by the linker because jump offsets are not |
| known before code is located. Therefore, the assembler code generated by the |
| compiler is the same, but the instructions in the executable may |
| differ from instructions in the assembler code. |
| |
| Relaxing must be turned on if linker stubs are needed, see the |
| section on @code{EIND} and linker stubs below. |
| |
| @item -mshort-calls |
| @opindex mshort-calls |
| Use @code{RCALL}/@code{RJMP} instructions even on devices with |
| 16@tie{}KiB or more of program memory, i.e.@: on devices that |
| have the @code{CALL} and @code{JMP} instructions. |
| See also the @code{-mrelax} command line option. |
| |
| @item -msp8 |
| @opindex msp8 |
| Treat the stack pointer register as an 8-bit register, |
| i.e.@: assume the high byte of the stack pointer is zero. |
| In general, you don't need to set this option by hand. |
| |
| This option is used internally by the compiler to select and |
| build multilibs for architectures @code{avr2} and @code{avr25}. |
| These architectures mix devices with and without @code{SPH}. |
| For any setting other than @code{-mmcu=avr2} or @code{-mmcu=avr25} |
| the compiler driver will add or remove this option from the compiler |
| proper's command line, because the compiler then knows if the device |
| or architecture has an 8-bit stack pointer and thus no @code{SPH} |
| register or not. |
| |
| @item -mstrict-X |
| @opindex mstrict-X |
| Use address register @code{X} in a way proposed by the hardware. This means |
| that @code{X} is only used in indirect, post-increment or |
| pre-decrement addressing. |
| |
| Without this option, the @code{X} register may be used in the same way |
| as @code{Y} or @code{Z} which then is emulated by additional |
| instructions. |
| For example, loading a value with @code{X+const} addressing with a |
| small non-negative @code{const < 64} to a register @var{Rn} is |
| performed as |
| |
| @example |
| adiw r26, const ; X += const |
| ld @var{Rn}, X ; @var{Rn} = *X |
| sbiw r26, const ; X -= const |
| @end example |
| |
| @item -mtiny-stack |
| @opindex mtiny-stack |
| Only change the lower 8@tie{}bits of the stack pointer. |
| @end table |
| |
| @subsubsection @code{EIND} and Devices with more than 128 Ki Bytes of Flash |
| @cindex @code{EIND} |
| Pointers in the implementation are 16@tie{}bits wide. |
| The address of a function or label is represented as word address so |
| that indirect jumps and calls can target any code address in the |
| range of 64@tie{}Ki words. |
| |
| In order to facilitate indirect jump on devices with more than 128@tie{}Ki |
| bytes of program memory space, there is a special function register called |
| @code{EIND} that serves as most significant part of the target address |
| when @code{EICALL} or @code{EIJMP} instructions are used. |
| |
| Indirect jumps and calls on these devices are handled as follows by |
| the compiler and are subject to some limitations: |
| |
| @itemize @bullet |
| |
| @item |
| The compiler never sets @code{EIND}. |
| |
| @item |
| The compiler uses @code{EIND} implicitely in @code{EICALL}/@code{EIJMP} |
| instructions or might read @code{EIND} directly in order to emulate an |
| indirect call/jump by means of a @code{RET} instruction. |
| |
| @item |
| The compiler assumes that @code{EIND} never changes during the startup |
| code or during the application. In particular, @code{EIND} is not |
| saved/restored in function or interrupt service routine |
| prologue/epilogue. |
| |
| @item |
| For indirect calls to functions and computed goto, the linker |
| generates @emph{stubs}. Stubs are jump pads sometimes also called |
| @emph{trampolines}. Thus, the indirect call/jump jumps to such a stub. |
| The stub contains a direct jump to the desired address. |
| |
| @item |
| Linker relaxation must be turned on so that the linker will generate |
| the stubs correctly an all situaltion. See the compiler option |
| @code{-mrelax} and the linler option @code{--relax}. |
| There are corner cases where the linker is supposed to generate stubs |
| but aborts without relaxation and without a helpful error message. |
| |
| @item |
| The default linker script is arranged for code with @code{EIND = 0}. |
| If code is supposed to work for a setup with @code{EIND != 0}, a custom |
| linker script has to be used in order to place the sections whose |
| name start with @code{.trampolines} into the segment where @code{EIND} |
| points to. |
| |
| @item |
| The startup code from libgcc never sets @code{EIND}. |
| Notice that startup code is a blend of code from libgcc and AVR-LibC. |
| For the impact of AVR-LibC on @code{EIND}, see the |
| @w{@uref{http://nongnu.org/avr-libc/user-manual,AVR-LibC user manual}}. |
| |
| @item |
| It is legitimate for user-specific startup code to set up @code{EIND} |
| early, for example by means of initialization code located in |
| section @code{.init3}. Such code runs prior to general startup code |
| that initializes RAM and calls constructors, but after the bit |
| of startup code from AVR-LibC that sets @code{EIND} to the segment |
| where the vector table is located. |
| @example |
| #include <avr/io.h> |
| |
| static void |
| __attribute__((section(".init3"),naked,used,no_instrument_function)) |
| init3_set_eind (void) |
| @{ |
| __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" |
| "out %i0,r24" :: "n" (&EIND) : "r24","memory"); |
| @} |
| @end example |
| |
| @noindent |
| The @code{__trampolines_start} symbol is defined in the linker script. |
| |
| @item |
| Stubs are generated automatically by the linker if |
| the following two conditions are met: |
| @itemize @minus |
| |
| @item The address of a label is taken by means of the @code{gs} modifier |
| (short for @emph{generate stubs}) like so: |
| @example |
| LDI r24, lo8(gs(@var{func})) |
| LDI r25, hi8(gs(@var{func})) |
| @end example |
| @item The final location of that label is in a code segment |
| @emph{outside} the segment where the stubs are located. |
| @end itemize |
| |
| @item |
| The compiler emits such @code{gs} modifiers for code labels in the |
| following situations: |
| @itemize @minus |
| @item Taking address of a function or code label. |
| @item Computed goto. |
| @item If prologue-save function is used, see @option{-mcall-prologues} |
| command-line option. |
| @item Switch/case dispatch tables. If you do not want such dispatch |
| tables you can specify the @option{-fno-jump-tables} command-line option. |
| @item C and C++ constructors/destructors called during startup/shutdown. |
| @item If the tools hit a @code{gs()} modifier explained above. |
| @end itemize |
| |
| @item |
| Jumping to non-symbolic addresses like so is @emph{not} supported: |
| |
| @example |
| int main (void) |
| @{ |
| /* Call function at word address 0x2 */ |
| return ((int(*)(void)) 0x2)(); |
| @} |
| @end example |
| |
| Instead, a stub has to be set up, i.e.@: the function has to be called |
| through a symbol (@code{func_4} in the example): |
| |
| @example |
| int main (void) |
| @{ |
| extern int func_4 (void); |
| |
| /* Call function at byte address 0x4 */ |
| return func_4(); |
| @} |
| @end example |
| |
| and the application be linked with @code{-Wl,--defsym,func_4=0x4}. |
| Alternatively, @code{func_4} can be defined in the linker script. |
| @end itemize |
| |
| @subsubsection Handling of the @code{RAMPD}, @code{RAMPX}, @code{RAMPY} and @code{RAMPZ} Special Function Registers |
| @cindex @code{RAMPD} |
| @cindex @code{RAMPX} |
| @cindex @code{RAMPY} |
| @cindex @code{RAMPZ} |
| Some AVR devices support memories larger than the 64@tie{}KiB range |
| that can be accessed with 16-bit pointers. To access memory locations |
| outside this 64@tie{}KiB range, the contentent of a @code{RAMP} |
| register is used as high part of the address: |
| The @code{X}, @code{Y}, @code{Z} address register is concatenated |
| with the @code{RAMPX}, @code{RAMPY}, @code{RAMPZ} special function |
| register, respectively, to get a wide address. Similarly, |
| @code{RAMPD} is used together with direct addressing. |
| |
| @itemize |
| @item |
| The startup code initializes the @code{RAMP} special function |
| registers with zero. |
| |
| @item |
| If a @ref{AVR Named Address Spaces,named address space} other than |
| generic or @code{__flash} is used, then @code{RAMPZ} is set |
| as needed before the operation. |
| |
| @item |
| If the device supports RAM larger than 64@tie{KiB} and the compiler |
| needs to change @code{RAMPZ} to accomplish an operation, @code{RAMPZ} |
| is reset to zero after the operation. |
| |
| @item |
| If the device comes with a specific @code{RAMP} register, the ISR |
| prologue/epilogue saves/restores that SFR and initializes it with |
| zero in case the ISR code might (implicitly) use it. |
| |
| @item |
| RAM larger than 64@tie{KiB} is not supported by GCC for AVR targets. |
| If you use inline assembler to read from locations outside the |
| 16-bit address range and change one of the @code{RAMP} registers, |
| you must reset it to zero after the access. |
| |
| @end itemize |
| |
| @subsubsection AVR Built-in Macros |
| |
| GCC defines several built-in macros so that the user code can test |
| for the presence or absence of features. Almost any of the following |
| built-in macros are deduced from device capabilities and thus |
| triggered by the @code{-mmcu=} command-line option. |
| |
| For even more AVR-specific built-in macros see |
| @ref{AVR Named Address Spaces} and @ref{AVR Built-in Functions}. |
| |
| @table @code |
| |
| @item __AVR_@var{Device}__ |
| Setting @code{-mmcu=@var{device}} defines this built-in macro which reflects |
| the device's name. For example, @code{-mmcu=atmega8} defines the |
| built-in macro @code{__AVR_ATmega8__}, @code{-mmcu=attiny261a} defines |
| @code{__AVR_ATtiny261A__}, etc. |
| |
| The built-in macros' names follow |
| the scheme @code{__AVR_@var{Device}__} where @var{Device} is |
| the device name as from the AVR user manual. The difference between |
| @var{Device} in the built-in macro and @var{device} in |
| @code{-mmcu=@var{device}} is that the latter is always lowercase. |
| |
| @item __AVR_HAVE_ELPM__ |
| The device has the the @code{ELPM} instruction. |
| |
| @item __AVR_HAVE_ELPMX__ |
| The device has the @code{ELPM R@var{n},Z} and @code{ELPM |
| R@var{n},Z+} instructions. |
| |
| @item __AVR_HAVE_MOVW__ |
| The device has the @code{MOVW} instruction to perform 16-bit |
| register-register moves. |
| |
| @item __AVR_HAVE_LPMX__ |
| The device has the @code{LPM R@var{n},Z} and |
| @code{LPM R@var{n},Z+} instructions. |
| |
| @item __AVR_HAVE_MUL__ |
| The device has a hardware multiplier. |
| |
| @item __AVR_HAVE_JMP_CALL__ |
| The device has the @code{JMP} and @code{CALL} instructions. |
| This is the case for devices with at least 16@tie{}KiB of program |
| memory and if @code{-mshort-calls} is not set. |
| |
| @item __AVR_HAVE_EIJMP_EICALL__ |
| @item __AVR_3_BYTE_PC__ |
| The device has the @code{EIJMP} and @code{EICALL} instructions. |
| This is the case for devices with more than 128@tie{}KiB of program memory. |
| This also means that the program counter |
| (PC) is 3@tie{}bytes wide. |
| |
| @item __AVR_2_BYTE_PC__ |
| The program counter (PC) is 2@tie{}bytes wide. This is the case for devices |
| with up to 128@tie{}KiB of program memory. |
| |
| @item __AVR_HAVE_8BIT_SP__ |
| @item __AVR_HAVE_16BIT_SP__ |
| The stack pointer (SP) register is treated as 8-bit respectively |
| 16-bit register by the compiler. |
| The definition of these macros is affected by @code{-mtiny-stack}. |
| |
| @item __AVR_HAVE_SPH__ |
| @item __AVR_SP8__ |
| The device has the SPH (high part of stack pointer) special function |
| register or has an 8-bit stack pointer, respectively. |
| The definition of these macros is affected by @code{-mmcu=} and |
| in the cases of @code{-mmcu=avr2} and @code{-mmcu=avr25} also |
| by @code{-msp8}. |
| |
| @item __AVR_HAVE_RAMPD__ |
| @item __AVR_HAVE_RAMPX__ |
| @item __AVR_HAVE_RAMPY__ |
| @item __AVR_HAVE_RAMPZ__ |
| The device has the @code{RAMPD}, @code{RAMPX}, @code{RAMPY}, |
| @code{RAMPZ} special function register, respectively. |
| |
| @item __NO_INTERRUPTS__ |
| This macro reflects the @code{-mno-interrupts} command line option. |
| |
| @item __AVR_ERRATA_SKIP__ |
| @item __AVR_ERRATA_SKIP_JMP_CALL__ |
| Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit |
| instructions because of a hardware erratum. Skip instructions are |
| @code{SBRS}, @code{SBRC}, @code{SBIS}, @code{SBIC} and @code{CPSE}. |
| The second macro is only defined if @code{__AVR_HAVE_JMP_CALL__} is also |
| set. |
| |
| @item __AVR_SFR_OFFSET__=@var{offset} |
| Instructions that can address I/O special function registers directly |
| like @code{IN}, @code{OUT}, @code{SBI}, etc.@: may use a different |
| address as if addressed by an instruction to access RAM like @code{LD} |
| or @code{STS}. This offset depends on the device architecture and has |
| to be subtracted from the RAM address in order to get the |
| respective I/O@tie{}address. |
| |
| @item __WITH_AVRLIBC__ |
| The compiler is configured to be used together with AVR-Libc. |
| See the @code{--with-avrlibc} configure option. |
| |
| @end table |
| |
| @node Blackfin Options |
| @subsection Blackfin Options |
| @cindex Blackfin Options |
| |
| @table @gcctabopt |
| @item -mcpu=@var{cpu}@r{[}-@var{sirevision}@r{]} |
| @opindex mcpu= |
| Specifies the name of the target Blackfin processor. Currently, @var{cpu} |
| can be one of @samp{bf512}, @samp{bf514}, @samp{bf516}, @samp{bf518}, |
| @samp{bf522}, @samp{bf523}, @samp{bf524}, @samp{bf525}, @samp{bf526}, |
| @samp{bf527}, @samp{bf531}, @samp{bf532}, @samp{bf533}, |
| @samp{bf534}, @samp{bf536}, @samp{bf537}, @samp{bf538}, @samp{bf539}, |
| @samp{bf542}, @samp{bf544}, @samp{bf547}, @samp{bf548}, @samp{bf549}, |
| @samp{bf542m}, @samp{bf544m}, @samp{bf547m}, @samp{bf548m}, @samp{bf549m}, |
| @samp{bf561}, @samp{bf592}. |
| |
| The optional @var{sirevision} specifies the silicon revision of the target |
| Blackfin processor. Any workarounds available for the targeted silicon revision |
| are enabled. If @var{sirevision} is @samp{none}, no workarounds are enabled. |
| If @var{sirevision} is @samp{any}, all workarounds for the targeted processor |
| are enabled. The @code{__SILICON_REVISION__} macro is defined to two |
| hexadecimal digits representing the major and minor numbers in the silicon |
| revision. If @var{sirevision} is @samp{none}, the @code{__SILICON_REVISION__} |
| is not defined. If @var{sirevision} is @samp{any}, the |
| @code{__SILICON_REVISION__} is defined to be @code{0xffff}. |
| If this optional @var{sirevision} is not used, GCC assumes the latest known |
| silicon revision of the targeted Blackfin processor. |
| |
| GCC defines a preprocessor macro for the specified @var{cpu}. |
| For the @samp{bfin-elf} toolchain, this option causes the hardware BSP |
| provided by libgloss to be linked in if @option{-msim} is not given. |
| |
| Without this option, @samp{bf532} is used as the processor by default. |
| |
| Note that support for @samp{bf561} is incomplete. For @samp{bf561}, |
| only the preprocessor macro is defined. |
| |
| @item -msim |
| @opindex msim |
| Specifies that the program will be run on the simulator. This causes |
| the simulator BSP provided by libgloss to be linked in. This option |
| has effect only for @samp{bfin-elf} toolchain. |
| Certain other options, such as @option{-mid-shared-library} and |
| @option{-mfdpic}, imply @option{-msim}. |
| |
| @item -momit-leaf-frame-pointer |
| @opindex momit-leaf-frame-pointer |
| Don't keep the frame pointer in a register for leaf functions. This |
| avoids the instructions to save, set up and restore frame pointers and |
| makes an extra register available in leaf functions. The option |
| @option{-fomit-frame-pointer} removes the frame pointer for all functions, |
| which might make debugging harder. |
| |
| @item -mspecld-anomaly |
| @opindex mspecld-anomaly |
| When enabled, the compiler ensures that the generated code does not |
| contain speculative loads after jump instructions. If this option is used, |
| @code{__WORKAROUND_SPECULATIVE_LOADS} is defined. |
| |
| @item -mno-specld-anomaly |
| @opindex mno-specld-anomaly |
| Don't generate extra code to prevent speculative loads from occurring. |
| |
| @item -mcsync-anomaly |
| @opindex mcsync-anomaly |
| When enabled, the compiler ensures that the generated code does not |
| contain CSYNC or SSYNC instructions too soon after conditional branches. |
| If this option is used, @code{__WORKAROUND_SPECULATIVE_SYNCS} is defined. |
| |
| @item -mno-csync-anomaly |
| @opindex mno-csync-anomaly |
| Don't generate extra code to prevent CSYNC or SSYNC instructions from |
| occurring too soon after a conditional branch. |
| |
| @item -mlow-64k |
| @opindex mlow-64k |
| When enabled, the compiler is free to take advantage of the knowledge that |
| the entire program fits into the low 64k of memory. |
| |
| @item -mno-low-64k |
| @opindex mno-low-64k |
| Assume that the program is arbitrarily large. This is the default. |
| |
| @item -mstack-check-l1 |
| @opindex mstack-check-l1 |
| Do stack checking using information placed into L1 scratchpad memory by the |
| uClinux kernel. |
| |
| @item -mid-shared-library |
| @opindex mid-shared-library |
| Generate code that supports shared libraries via the library ID method. |
| This allows for execute in place and shared libraries in an environment |
| without virtual memory management. This option implies @option{-fPIC}. |
| With a @samp{bfin-elf} target, this option implies @option{-msim}. |
| |
| @item -mno-id-shared-library |
| @opindex mno-id-shared-library |
| Generate code that doesn't assume ID-based shared libraries are being used. |
| This is the default. |
| |
| @item -mleaf-id-shared-library |
| @opindex mleaf-id-shared-library |
| Generate code that supports shared libraries via the library ID method, |
| but assumes that this library or executable won't link against any other |
| ID shared libraries. That allows the compiler to use faster code for jumps |
| and calls. |
| |
| @item -mno-leaf-id-shared-library |
| @opindex mno-leaf-id-shared-library |
| Do not assume that the code being compiled won't link against any ID shared |
| libraries. Slower code is generated for jump and call insns. |
| |
| @item -mshared-library-id=n |
| @opindex mshared-library-id |
| Specifies the identification number of the ID-based shared library being |
| compiled. Specifying a value of 0 generates more compact code; specifying |
| other values forces the allocation of that number to the current |
| library but is no more space- or time-efficient than omitting this option. |
| |
| @item -msep-data |
| @opindex msep-data |
| Generate code that allows the data segment to be located in a different |
| area of memory from the text segment. This allows for execute in place in |
| an environment without virtual memory management by eliminating relocations |
| against the text section. |
| |
| @item -mno-sep-data |
| @opindex mno-sep-data |
| Generate code that assumes that the data segment follows the text segment. |
| This is the default. |
| |
| @item -mlong-calls |
| @itemx -mno-long-calls |
| @opindex mlong-calls |
| @opindex mno-long-calls |
| Tells the compiler to perform function calls by first loading the |
| address of the function into a register and then performing a subroutine |
| call on this register. This switch is needed if the target function |
| lies outside of the 24-bit addressing range of the offset-based |
| version of subroutine call instruction. |
| |
| This feature is not enabled by default. Specifying |
| @option{-mno-long-calls} restores the default behavior. Note these |
| switches have no effect on how the compiler generates code to handle |
| function calls via function pointers. |
| |
| @item -mfast-fp |
| @opindex mfast-fp |
| Link with the fast floating-point library. This library relaxes some of |
| the IEEE floating-point standard's rules for checking inputs against |
| Not-a-Number (NAN), in the interest of performance. |
| |
| @item -minline-plt |
| @opindex minline-plt |
| Enable inlining of PLT entries in function calls to functions that are |
| not known to bind locally. It has no effect without @option{-mfdpic}. |
| |
| @item -mmulticore |
| @opindex mmulticore |
| Build a standalone application for multicore Blackfin processors. |
| This option causes proper start files and link scripts supporting |
| multicore to be used, and defines the macro @code{__BFIN_MULTICORE}. |
| It can only be used with @option{-mcpu=bf561@r{[}-@var{sirevision}@r{]}}. |
| |
| This option can be used with @option{-mcorea} or @option{-mcoreb}, which |
| selects the one-application-per-core programming model. Without |
| @option{-mcorea} or @option{-mcoreb}, the single-application/dual-core |
| programming model is used. In this model, the main function of Core B |
| should be named as @code{coreb_main}. |
| |
| If this option is not used, the single-core application programming |
| model is used. |
| |
| @item -mcorea |
| @opindex mcorea |
| Build a standalone application for Core A of BF561 when using |
| the one-application-per-core programming model. Proper start files |
| and link scripts are used to support Core A, and the macro |
| @code{__BFIN_COREA} is defined. |
| This option can only be used in conjunction with @option{-mmulticore}. |
| |
| @item -mcoreb |
| @opindex mcoreb |
| Build a standalone application for Core B of BF561 when using |
| the one-application-per-core programming model. Proper start files |
| and link scripts are used to support Core B, and the macro |
| @code{__BFIN_COREB} is defined. When this option is used, @code{coreb_main} |
| should be used instead of @code{main}. |
| This option can only be used in conjunction with @option{-mmulticore}. |
| |
| @item -msdram |
| @opindex msdram |
| Build a standalone application for SDRAM. Proper start files and |
| link scripts are used to put the application into SDRAM, and the macro |
| @code{__BFIN_SDRAM} is defined. |
| The loader should initialize SDRAM before loading the application. |
| |
| @item -micplb |
| @opindex micplb |
| Assume that ICPLBs are enabled at run time. This has an effect on certain |
| anomaly workarounds. For Linux targets, the default is to assume ICPLBs |
| are enabled; for standalone applications the default is off. |
| @end table |
| |
| @node C6X Options |
| @subsection C6X Options |
| @cindex C6X Options |
| |
| @table @gcctabopt |
| @item -march=@var{name} |
| @opindex march |
| This specifies the name of the target architecture. GCC uses this |
| name to determine what kind of instructions it can emit when generating |
| assembly code. Permissible names are: @samp{c62x}, |
| @samp{c64x}, @samp{c64x+}, @samp{c67x}, @samp{c67x+}, @samp{c674x}. |
| |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate code for a big-endian target. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate code for a little-endian target. This is the default. |
| |
| @item -msim |
| @opindex msim |
| Choose startup files and linker script suitable for the simulator. |
| |
| @item -msdata=default |
| @opindex msdata=default |
| Put small global and static data in the @samp{.neardata} section, |
| which is pointed to by register @code{B14}. Put small uninitialized |
| global and static data in the @samp{.bss} section, which is adjacent |
| to the @samp{.neardata} section. Put small read-only data into the |
| @samp{.rodata} section. The corresponding sections used for large |
| pieces of data are @samp{.fardata}, @samp{.far} and @samp{.const}. |
| |
| @item -msdata=all |
| @opindex msdata=all |
| Put all data, not just small objects, into the sections reserved for |
| small data, and use addressing relative to the @code{B14} register to |
| access them. |
| |
| @item -msdata=none |
| @opindex msdata=none |
| Make no use of the sections reserved for small data, and use absolute |
| addresses to access all data. Put all initialized global and static |
| data in the @samp{.fardata} section, and all uninitialized data in the |
| @samp{.far} section. Put all constant data into the @samp{.const} |
| section. |
| @end table |
| |
| @node CRIS Options |
| @subsection CRIS Options |
| @cindex CRIS Options |
| |
| These options are defined specifically for the CRIS ports. |
| |
| @table @gcctabopt |
| @item -march=@var{architecture-type} |
| @itemx -mcpu=@var{architecture-type} |
| @opindex march |
| @opindex mcpu |
| Generate code for the specified architecture. The choices for |
| @var{architecture-type} are @samp{v3}, @samp{v8} and @samp{v10} for |
| respectively ETRAX@w{ }4, ETRAX@w{ }100, and ETRAX@w{ }100@w{ }LX@. |
| Default is @samp{v0} except for cris-axis-linux-gnu, where the default is |
| @samp{v10}. |
| |
| @item -mtune=@var{architecture-type} |
| @opindex mtune |
| Tune to @var{architecture-type} everything applicable about the generated |
| code, except for the ABI and the set of available instructions. The |
| choices for @var{architecture-type} are the same as for |
| @option{-march=@var{architecture-type}}. |
| |
| @item -mmax-stack-frame=@var{n} |
| @opindex mmax-stack-frame |
| Warn when the stack frame of a function exceeds @var{n} bytes. |
| |
| @item -metrax4 |
| @itemx -metrax100 |
| @opindex metrax4 |
| @opindex metrax100 |
| The options @option{-metrax4} and @option{-metrax100} are synonyms for |
| @option{-march=v3} and @option{-march=v8} respectively. |
| |
| @item -mmul-bug-workaround |
| @itemx -mno-mul-bug-workaround |
| @opindex mmul-bug-workaround |
| @opindex mno-mul-bug-workaround |
| Work around a bug in the @code{muls} and @code{mulu} instructions for CPU |
| models where it applies. This option is active by default. |
| |
| @item -mpdebug |
| @opindex mpdebug |
| Enable CRIS-specific verbose debug-related information in the assembly |
| code. This option also has the effect of turning off the @samp{#NO_APP} |
| formatted-code indicator to the assembler at the beginning of the |
| assembly file. |
| |
| @item -mcc-init |
| @opindex mcc-init |
| Do not use condition-code results from previous instruction; always emit |
| compare and test instructions before use of condition codes. |
| |
| @item -mno-side-effects |
| @opindex mno-side-effects |
| Do not emit instructions with side effects in addressing modes other than |
| post-increment. |
| |
| @item -mstack-align |
| @itemx -mno-stack-align |
| @itemx -mdata-align |
| @itemx -mno-data-align |
| @itemx -mconst-align |
| @itemx -mno-const-align |
| @opindex mstack-align |
| @opindex mno-stack-align |
| @opindex mdata-align |
| @opindex mno-data-align |
| @opindex mconst-align |
| @opindex mno-const-align |
| These options (@samp{no-} options) arrange (eliminate arrangements) for the |
| stack frame, individual data and constants to be aligned for the maximum |
| single data access size for the chosen CPU model. The default is to |
| arrange for 32-bit alignment. ABI details such as structure layout are |
| not affected by these options. |
| |
| @item -m32-bit |
| @itemx -m16-bit |
| @itemx -m8-bit |
| @opindex m32-bit |
| @opindex m16-bit |
| @opindex m8-bit |
| Similar to the stack- data- and const-align options above, these options |
| arrange for stack frame, writable data and constants to all be 32-bit, |
| 16-bit or 8-bit aligned. The default is 32-bit alignment. |
| |
| @item -mno-prologue-epilogue |
| @itemx -mprologue-epilogue |
| @opindex mno-prologue-epilogue |
| @opindex mprologue-epilogue |
| With @option{-mno-prologue-epilogue}, the normal function prologue and |
| epilogue which set up the stack frame are omitted and no return |
| instructions or return sequences are generated in the code. Use this |
| option only together with visual inspection of the compiled code: no |
| warnings or errors are generated when call-saved registers must be saved, |
| or storage for local variables needs to be allocated. |
| |
| @item -mno-gotplt |
| @itemx -mgotplt |
| @opindex mno-gotplt |
| @opindex mgotplt |
| With @option{-fpic} and @option{-fPIC}, don't generate (do generate) |
| instruction sequences that load addresses for functions from the PLT part |
| of the GOT rather than (traditional on other architectures) calls to the |
| PLT@. The default is @option{-mgotplt}. |
| |
| @item -melf |
| @opindex melf |
| Legacy no-op option only recognized with the cris-axis-elf and |
| cris-axis-linux-gnu targets. |
| |
| @item -mlinux |
| @opindex mlinux |
| Legacy no-op option only recognized with the cris-axis-linux-gnu target. |
| |
| @item -sim |
| @opindex sim |
| This option, recognized for the cris-axis-elf, arranges |
| to link with input-output functions from a simulator library. Code, |
| initialized data and zero-initialized data are allocated consecutively. |
| |
| @item -sim2 |
| @opindex sim2 |
| Like @option{-sim}, but pass linker options to locate initialized data at |
| 0x40000000 and zero-initialized data at 0x80000000. |
| @end table |
| |
| @node CR16 Options |
| @subsection CR16 Options |
| @cindex CR16 Options |
| |
| These options are defined specifically for the CR16 ports. |
| |
| @table @gcctabopt |
| |
| @item -mmac |
| @opindex mmac |
| Enable the use of multiply-accumulate instructions. Disabled by default. |
| |
| @item -mcr16cplus |
| @itemx -mcr16c |
| @opindex mcr16cplus |
| @opindex mcr16c |
| Generate code for CR16C or CR16C+ architecture. CR16C+ architecture |
| is default. |
| |
| @item -msim |
| @opindex msim |
| Links the library libsim.a which is in compatible with simulator. Applicable |
| to ELF compiler only. |
| |
| @item -mint32 |
| @opindex mint32 |
| Choose integer type as 32-bit wide. |
| |
| @item -mbit-ops |
| @opindex mbit-ops |
| Generates @code{sbit}/@code{cbit} instructions for bit manipulations. |
| |
| @item -mdata-model=@var{model} |
| @opindex mdata-model |
| Choose a data model. The choices for @var{model} are @samp{near}, |
| @samp{far} or @samp{medium}. @samp{medium} is default. |
| However, @samp{far} is not valid with @option{-mcr16c}, as the |
| CR16C architecture does not support the far data model. |
| @end table |
| |
| @node Darwin Options |
| @subsection Darwin Options |
| @cindex Darwin options |
| |
| These options are defined for all architectures running the Darwin operating |
| system. |
| |
| FSF GCC on Darwin does not create ``fat'' object files; it creates |
| an object file for the single architecture that GCC was built to |
| target. Apple's GCC on Darwin does create ``fat'' files if multiple |
| @option{-arch} options are used; it does so by running the compiler or |
| linker multiple times and joining the results together with |
| @file{lipo}. |
| |
| The subtype of the file created (like @samp{ppc7400} or @samp{ppc970} or |
| @samp{i686}) is determined by the flags that specify the ISA |
| that GCC is targetting, like @option{-mcpu} or @option{-march}. The |
| @option{-force_cpusubtype_ALL} option can be used to override this. |
| |
| The Darwin tools vary in their behavior when presented with an ISA |
| mismatch. The assembler, @file{as}, only permits instructions to |
| be used that are valid for the subtype of the file it is generating, |
| so you cannot put 64-bit instructions in a @samp{ppc750} object file. |
| The linker for shared libraries, @file{/usr/bin/libtool}, fails |
| and prints an error if asked to create a shared library with a less |
| restrictive subtype than its input files (for instance, trying to put |
| a @samp{ppc970} object file in a @samp{ppc7400} library). The linker |
| for executables, @command{ld}, quietly gives the executable the most |
| restrictive subtype of any of its input files. |
| |
| @table @gcctabopt |
| @item -F@var{dir} |
| @opindex F |
| Add the framework directory @var{dir} to the head of the list of |
| directories to be searched for header files. These directories are |
| interleaved with those specified by @option{-I} options and are |
| scanned in a left-to-right order. |
| |
| A framework directory is a directory with frameworks in it. A |
| framework is a directory with a @file{Headers} and/or |
| @file{PrivateHeaders} directory contained directly in it that ends |
| in @file{.framework}. The name of a framework is the name of this |
| directory excluding the @file{.framework}. Headers associated with |
| the framework are found in one of those two directories, with |
| @file{Headers} being searched first. A subframework is a framework |
| directory that is in a framework's @file{Frameworks} directory. |
| Includes of subframework headers can only appear in a header of a |
| framework that contains the subframework, or in a sibling subframework |
| header. Two subframeworks are siblings if they occur in the same |
| framework. A subframework should not have the same name as a |
| framework; a warning is issued if this is violated. Currently a |
| subframework cannot have subframeworks; in the future, the mechanism |
| may be extended to support this. The standard frameworks can be found |
| in @file{/System/Library/Frameworks} and |
| @file{/Library/Frameworks}. An example include looks like |
| @code{#include <Framework/header.h>}, where @file{Framework} denotes |
| the name of the framework and @file{header.h} is found in the |
| @file{PrivateHeaders} or @file{Headers} directory. |
| |
| @item -iframework@var{dir} |
| @opindex iframework |
| Like @option{-F} except the directory is a treated as a system |
| directory. The main difference between this @option{-iframework} and |
| @option{-F} is that with @option{-iframework} the compiler does not |
| warn about constructs contained within header files found via |
| @var{dir}. This option is valid only for the C family of languages. |
| |
| @item -gused |
| @opindex gused |
| Emit debugging information for symbols that are used. For stabs |
| debugging format, this enables @option{-feliminate-unused-debug-symbols}. |
| This is by default ON@. |
| |
| @item -gfull |
| @opindex gfull |
| Emit debugging information for all symbols and types. |
| |
| @item -mmacosx-version-min=@var{version} |
| The earliest version of MacOS X that this executable will run on |
| is @var{version}. Typical values of @var{version} include @code{10.1}, |
| @code{10.2}, and @code{10.3.9}. |
| |
| If the compiler was built to use the system's headers by default, |
| then the default for this option is the system version on which the |
| compiler is running, otherwise the default is to make choices that |
| are compatible with as many systems and code bases as possible. |
| |
| @item -mkernel |
| @opindex mkernel |
| Enable kernel development mode. The @option{-mkernel} option sets |
| @option{-static}, @option{-fno-common}, @option{-fno-cxa-atexit}, |
| @option{-fno-exceptions}, @option{-fno-non-call-exceptions}, |
| @option{-fapple-kext}, @option{-fno-weak} and @option{-fno-rtti} where |
| applicable. This mode also sets @option{-mno-altivec}, |
| @option{-msoft-float}, @option{-fno-builtin} and |
| @option{-mlong-branch} for PowerPC targets. |
| |
| @item -mone-byte-bool |
| @opindex mone-byte-bool |
| Override the defaults for @samp{bool} so that @samp{sizeof(bool)==1}. |
| By default @samp{sizeof(bool)} is @samp{4} when compiling for |
| Darwin/PowerPC and @samp{1} when compiling for Darwin/x86, so this |
| option has no effect on x86. |
| |
| @strong{Warning:} The @option{-mone-byte-bool} switch causes GCC |
| to generate code that is not binary compatible with code generated |
| without that switch. Using this switch may require recompiling all |
| other modules in a program, including system libraries. Use this |
| switch to conform to a non-default data model. |
| |
| @item -mfix-and-continue |
| @itemx -ffix-and-continue |
| @itemx -findirect-data |
| @opindex mfix-and-continue |
| @opindex ffix-and-continue |
| @opindex findirect-data |
| Generate code suitable for fast turnaround development, such as to |
| allow GDB to dynamically load @code{.o} files into already-running |
| programs. @option{-findirect-data} and @option{-ffix-and-continue} |
| are provided for backwards compatibility. |
| |
| @item -all_load |
| @opindex all_load |
| Loads all members of static archive libraries. |
| See man ld(1) for more information. |
| |
| @item -arch_errors_fatal |
| @opindex arch_errors_fatal |
| Cause the errors having to do with files that have the wrong architecture |
| to be fatal. |
| |
| @item -bind_at_load |
| @opindex bind_at_load |
| Causes the output file to be marked such that the dynamic linker will |
| bind all undefined references when the file is loaded or launched. |
| |
| @item -bundle |
| @opindex bundle |
| Produce a Mach-o bundle format file. |
| See man ld(1) for more information. |
| |
| @item -bundle_loader @var{executable} |
| @opindex bundle_loader |
| This option specifies the @var{executable} that will load the build |
| output file being linked. See man ld(1) for more information. |
| |
| @item -dynamiclib |
| @opindex dynamiclib |
| When passed this option, GCC produces a dynamic library instead of |
| an executable when linking, using the Darwin @file{libtool} command. |
| |
| @item -force_cpusubtype_ALL |
| @opindex force_cpusubtype_ALL |
| This causes GCC's output file to have the @var{ALL} subtype, instead of |
| one controlled by the @option{-mcpu} or @option{-march} option. |
| |
| @item -allowable_client @var{client_name} |
| @itemx -client_name |
| @itemx -compatibility_version |
| @itemx -current_version |
| @itemx -dead_strip |
| @itemx -dependency-file |
| @itemx -dylib_file |
| @itemx -dylinker_install_name |
| @itemx -dynamic |
| @itemx -exported_symbols_list |
| @itemx -filelist |
| @need 800 |
| @itemx -flat_namespace |
| @itemx -force_flat_namespace |
| @itemx -headerpad_max_install_names |
| @itemx -image_base |
| @itemx -init |
| @itemx -install_name |
| @itemx -keep_private_externs |
| @itemx -multi_module |
| @itemx -multiply_defined |
| @itemx -multiply_defined_unused |
| @need 800 |
| @itemx -noall_load |
| @itemx -no_dead_strip_inits_and_terms |
| @itemx -nofixprebinding |
| @itemx -nomultidefs |
| @itemx -noprebind |
| @itemx -noseglinkedit |
| @itemx -pagezero_size |
| @itemx -prebind |
| @itemx -prebind_all_twolevel_modules |
| @itemx -private_bundle |
| @need 800 |
| @itemx -read_only_relocs |
| @itemx -sectalign |
| @itemx -sectobjectsymbols |
| @itemx -whyload |
| @itemx -seg1addr |
| @itemx -sectcreate |
| @itemx -sectobjectsymbols |
| @itemx -sectorder |
| @itemx -segaddr |
| @itemx -segs_read_only_addr |
| @need 800 |
| @itemx -segs_read_write_addr |
| @itemx -seg_addr_table |
| @itemx -seg_addr_table_filename |
| @itemx -seglinkedit |
| @itemx -segprot |
| @itemx -segs_read_only_addr |
| @itemx -segs_read_write_addr |
| @itemx -single_module |
| @itemx -static |
| @itemx -sub_library |
| @need 800 |
| @itemx -sub_umbrella |
| @itemx -twolevel_namespace |
| @itemx -umbrella |
| @itemx -undefined |
| @itemx -unexported_symbols_list |
| @itemx -weak_reference_mismatches |
| @itemx -whatsloaded |
| @opindex allowable_client |
| @opindex client_name |
| @opindex compatibility_version |
| @opindex current_version |
| @opindex dead_strip |
| @opindex dependency-file |
| @opindex dylib_file |
| @opindex dylinker_install_name |
| @opindex dynamic |
| @opindex exported_symbols_list |
| @opindex filelist |
| @opindex flat_namespace |
| @opindex force_flat_namespace |
| @opindex headerpad_max_install_names |
| @opindex image_base |
| @opindex init |
| @opindex install_name |
| @opindex keep_private_externs |
| @opindex multi_module |
| @opindex multiply_defined |
| @opindex multiply_defined_unused |
| @opindex noall_load |
| @opindex no_dead_strip_inits_and_terms |
| @opindex nofixprebinding |
| @opindex nomultidefs |
| @opindex noprebind |
| @opindex noseglinkedit |
| @opindex pagezero_size |
| @opindex prebind |
| @opindex prebind_all_twolevel_modules |
| @opindex private_bundle |
| @opindex read_only_relocs |
| @opindex sectalign |
| @opindex sectobjectsymbols |
| @opindex whyload |
| @opindex seg1addr |
| @opindex sectcreate |
| @opindex sectobjectsymbols |
| @opindex sectorder |
| @opindex segaddr |
| @opindex segs_read_only_addr |
| @opindex segs_read_write_addr |
| @opindex seg_addr_table |
| @opindex seg_addr_table_filename |
| @opindex seglinkedit |
| @opindex segprot |
| @opindex segs_read_only_addr |
| @opindex segs_read_write_addr |
| @opindex single_module |
| @opindex static |
| @opindex sub_library |
| @opindex sub_umbrella |
| @opindex twolevel_namespace |
| @opindex umbrella |
| @opindex undefined |
| @opindex unexported_symbols_list |
| @opindex weak_reference_mismatches |
| @opindex whatsloaded |
| These options are passed to the Darwin linker. The Darwin linker man page |
| describes them in detail. |
| @end table |
| |
| @node DEC Alpha Options |
| @subsection DEC Alpha Options |
| |
| These @samp{-m} options are defined for the DEC Alpha implementations: |
| |
| @table @gcctabopt |
| @item -mno-soft-float |
| @itemx -msoft-float |
| @opindex mno-soft-float |
| @opindex msoft-float |
| Use (do not use) the hardware floating-point instructions for |
| floating-point operations. When @option{-msoft-float} is specified, |
| functions in @file{libgcc.a} are used to perform floating-point |
| operations. Unless they are replaced by routines that emulate the |
| floating-point operations, or compiled in such a way as to call such |
| emulations routines, these routines issue floating-point |
| operations. If you are compiling for an Alpha without floating-point |
| operations, you must ensure that the library is built so as not to call |
| them. |
| |
| Note that Alpha implementations without floating-point operations are |
| required to have floating-point registers. |
| |
| @item -mfp-reg |
| @itemx -mno-fp-regs |
| @opindex mfp-reg |
| @opindex mno-fp-regs |
| Generate code that uses (does not use) the floating-point register set. |
| @option{-mno-fp-regs} implies @option{-msoft-float}. If the floating-point |
| register set is not used, floating-point operands are passed in integer |
| registers as if they were integers and floating-point results are passed |
| in @code{$0} instead of @code{$f0}. This is a non-standard calling sequence, |
| so any function with a floating-point argument or return value called by code |
| compiled with @option{-mno-fp-regs} must also be compiled with that |
| option. |
| |
| A typical use of this option is building a kernel that does not use, |
| and hence need not save and restore, any floating-point registers. |
| |
| @item -mieee |
| @opindex mieee |
| The Alpha architecture implements floating-point hardware optimized for |
| maximum performance. It is mostly compliant with the IEEE floating-point |
| standard. However, for full compliance, software assistance is |
| required. This option generates code fully IEEE-compliant code |
| @emph{except} that the @var{inexact-flag} is not maintained (see below). |
| If this option is turned on, the preprocessor macro @code{_IEEE_FP} is |
| defined during compilation. The resulting code is less efficient but is |
| able to correctly support denormalized numbers and exceptional IEEE |
| values such as not-a-number and plus/minus infinity. Other Alpha |
| compilers call this option @option{-ieee_with_no_inexact}. |
| |
| @item -mieee-with-inexact |
| @opindex mieee-with-inexact |
| This is like @option{-mieee} except the generated code also maintains |
| the IEEE @var{inexact-flag}. Turning on this option causes the |
| generated code to implement fully-compliant IEEE math. In addition to |
| @code{_IEEE_FP}, @code{_IEEE_FP_EXACT} is defined as a preprocessor |
| macro. On some Alpha implementations the resulting code may execute |
| significantly slower than the code generated by default. Since there is |
| very little code that depends on the @var{inexact-flag}, you should |
| normally not specify this option. Other Alpha compilers call this |
| option @option{-ieee_with_inexact}. |
| |
| @item -mfp-trap-mode=@var{trap-mode} |
| @opindex mfp-trap-mode |
| This option controls what floating-point related traps are enabled. |
| Other Alpha compilers call this option @option{-fptm @var{trap-mode}}. |
| The trap mode can be set to one of four values: |
| |
| @table @samp |
| @item n |
| This is the default (normal) setting. The only traps that are enabled |
| are the ones that cannot be disabled in software (e.g., division by zero |
| trap). |
| |
| @item u |
| In addition to the traps enabled by @samp{n}, underflow traps are enabled |
| as well. |
| |
| @item su |
| Like @samp{u}, but the instructions are marked to be safe for software |
| completion (see Alpha architecture manual for details). |
| |
| @item sui |
| Like @samp{su}, but inexact traps are enabled as well. |
| @end table |
| |
| @item -mfp-rounding-mode=@var{rounding-mode} |
| @opindex mfp-rounding-mode |
| Selects the IEEE rounding mode. Other Alpha compilers call this option |
| @option{-fprm @var{rounding-mode}}. The @var{rounding-mode} can be one |
| of: |
| |
| @table @samp |
| @item n |
| Normal IEEE rounding mode. Floating-point numbers are rounded towards |
| the nearest machine number or towards the even machine number in case |
| of a tie. |
| |
| @item m |
| Round towards minus infinity. |
| |
| @item c |
| Chopped rounding mode. Floating-point numbers are rounded towards zero. |
| |
| @item d |
| Dynamic rounding mode. A field in the floating-point control register |
| (@var{fpcr}, see Alpha architecture reference manual) controls the |
| rounding mode in effect. The C library initializes this register for |
| rounding towards plus infinity. Thus, unless your program modifies the |
| @var{fpcr}, @samp{d} corresponds to round towards plus infinity. |
| @end table |
| |
| @item -mtrap-precision=@var{trap-precision} |
| @opindex mtrap-precision |
| In the Alpha architecture, floating-point traps are imprecise. This |
| means without software assistance it is impossible to recover from a |
| floating trap and program execution normally needs to be terminated. |
| GCC can generate code that can assist operating system trap handlers |
| in determining the exact location that caused a floating-point trap. |
| Depending on the requirements of an application, different levels of |
| precisions can be selected: |
| |
| @table @samp |
| @item p |
| Program precision. This option is the default and means a trap handler |
| can only identify which program caused a floating-point exception. |
| |
| @item f |
| Function precision. The trap handler can determine the function that |
| caused a floating-point exception. |
| |
| @item i |
| Instruction precision. The trap handler can determine the exact |
| instruction that caused a floating-point exception. |
| @end table |
| |
| Other Alpha compilers provide the equivalent options called |
| @option{-scope_safe} and @option{-resumption_safe}. |
| |
| @item -mieee-conformant |
| @opindex mieee-conformant |
| This option marks the generated code as IEEE conformant. You must not |
| use this option unless you also specify @option{-mtrap-precision=i} and either |
| @option{-mfp-trap-mode=su} or @option{-mfp-trap-mode=sui}. Its only effect |
| is to emit the line @samp{.eflag 48} in the function prologue of the |
| generated assembly file. |
| |
| @item -mbuild-constants |
| @opindex mbuild-constants |
| Normally GCC examines a 32- or 64-bit integer constant to |
| see if it can construct it from smaller constants in two or three |
| instructions. If it cannot, it outputs the constant as a literal and |
| generates code to load it from the data segment at run time. |
| |
| Use this option to require GCC to construct @emph{all} integer constants |
| using code, even if it takes more instructions (the maximum is six). |
| |
| You typically use this option to build a shared library dynamic |
| loader. Itself a shared library, it must relocate itself in memory |
| before it can find the variables and constants in its own data segment. |
| |
| @item -mbwx |
| @itemx -mno-bwx |
| @itemx -mcix |
| @itemx -mno-cix |
| @itemx -mfix |
| @itemx -mno-fix |
| @itemx -mmax |
| @itemx -mno-max |
| @opindex mbwx |
| @opindex mno-bwx |
| @opindex mcix |
| @opindex mno-cix |
| @opindex mfix |
| @opindex mno-fix |
| @opindex mmax |
| @opindex mno-max |
| Indicate whether GCC should generate code to use the optional BWX, |
| CIX, FIX and MAX instruction sets. The default is to use the instruction |
| sets supported by the CPU type specified via @option{-mcpu=} option or that |
| of the CPU on which GCC was built if none is specified. |
| |
| @item -mfloat-vax |
| @itemx -mfloat-ieee |
| @opindex mfloat-vax |
| @opindex mfloat-ieee |
| Generate code that uses (does not use) VAX F and G floating-point |
| arithmetic instead of IEEE single and double precision. |
| |
| @item -mexplicit-relocs |
| @itemx -mno-explicit-relocs |
| @opindex mexplicit-relocs |
| @opindex mno-explicit-relocs |
| Older Alpha assemblers provided no way to generate symbol relocations |
| except via assembler macros. Use of these macros does not allow |
| optimal instruction scheduling. GNU binutils as of version 2.12 |
| supports a new syntax that allows the compiler to explicitly mark |
| which relocations should apply to which instructions. This option |
| is mostly useful for debugging, as GCC detects the capabilities of |
| the assembler when it is built and sets the default accordingly. |
| |
| @item -msmall-data |
| @itemx -mlarge-data |
| @opindex msmall-data |
| @opindex mlarge-data |
| When @option{-mexplicit-relocs} is in effect, static data is |
| accessed via @dfn{gp-relative} relocations. When @option{-msmall-data} |
| is used, objects 8 bytes long or smaller are placed in a @dfn{small data area} |
| (the @code{.sdata} and @code{.sbss} sections) and are accessed via |
| 16-bit relocations off of the @code{$gp} register. This limits the |
| size of the small data area to 64KB, but allows the variables to be |
| directly accessed via a single instruction. |
| |
| The default is @option{-mlarge-data}. With this option the data area |
| is limited to just below 2GB@. Programs that require more than 2GB of |
| data must use @code{malloc} or @code{mmap} to allocate the data in the |
| heap instead of in the program's data segment. |
| |
| When generating code for shared libraries, @option{-fpic} implies |
| @option{-msmall-data} and @option{-fPIC} implies @option{-mlarge-data}. |
| |
| @item -msmall-text |
| @itemx -mlarge-text |
| @opindex msmall-text |
| @opindex mlarge-text |
| When @option{-msmall-text} is used, the compiler assumes that the |
| code of the entire program (or shared library) fits in 4MB, and is |
| thus reachable with a branch instruction. When @option{-msmall-data} |
| is used, the compiler can assume that all local symbols share the |
| same @code{$gp} value, and thus reduce the number of instructions |
| required for a function call from 4 to 1. |
| |
| The default is @option{-mlarge-text}. |
| |
| @item -mcpu=@var{cpu_type} |
| @opindex mcpu |
| Set the instruction set and instruction scheduling parameters for |
| machine type @var{cpu_type}. You can specify either the @samp{EV} |
| style name or the corresponding chip number. GCC supports scheduling |
| parameters for the EV4, EV5 and EV6 family of processors and |
| chooses the default values for the instruction set from the processor |
| you specify. If you do not specify a processor type, GCC defaults |
| to the processor on which the compiler was built. |
| |
| Supported values for @var{cpu_type} are |
| |
| @table @samp |
| @item ev4 |
| @itemx ev45 |
| @itemx 21064 |
| Schedules as an EV4 and has no instruction set extensions. |
| |
| @item ev5 |
| @itemx 21164 |
| Schedules as an EV5 and has no instruction set extensions. |
| |
| @item ev56 |
| @itemx 21164a |
| Schedules as an EV5 and supports the BWX extension. |
| |
| @item pca56 |
| @itemx 21164pc |
| @itemx 21164PC |
| Schedules as an EV5 and supports the BWX and MAX extensions. |
| |
| @item ev6 |
| @itemx 21264 |
| Schedules as an EV6 and supports the BWX, FIX, and MAX extensions. |
| |
| @item ev67 |
| @itemx 21264a |
| Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX extensions. |
| @end table |
| |
| Native toolchains also support the value @samp{native}, |
| which selects the best architecture option for the host processor. |
| @option{-mcpu=native} has no effect if GCC does not recognize |
| the processor. |
| |
| @item -mtune=@var{cpu_type} |
| @opindex mtune |
| Set only the instruction scheduling parameters for machine type |
| @var{cpu_type}. The instruction set is not changed. |
| |
| Native toolchains also support the value @samp{native}, |
| which selects the best architecture option for the host processor. |
| @option{-mtune=native} has no effect if GCC does not recognize |
| the processor. |
| |
| @item -mmemory-latency=@var{time} |
| @opindex mmemory-latency |
| Sets the latency the scheduler should assume for typical memory |
| references as seen by the application. This number is highly |
| dependent on the memory access patterns used by the application |
| and the size of the external cache on the machine. |
| |
| Valid options for @var{time} are |
| |
| @table @samp |
| @item @var{number} |
| A decimal number representing clock cycles. |
| |
| @item L1 |
| @itemx L2 |
| @itemx L3 |
| @itemx main |
| The compiler contains estimates of the number of clock cycles for |
| ``typical'' EV4 & EV5 hardware for the Level 1, 2 & 3 caches |
| (also called Dcache, Scache, and Bcache), as well as to main memory. |
| Note that L3 is only valid for EV5. |
| |
| @end table |
| @end table |
| |
| @node FR30 Options |
| @subsection FR30 Options |
| @cindex FR30 Options |
| |
| These options are defined specifically for the FR30 port. |
| |
| @table @gcctabopt |
| |
| @item -msmall-model |
| @opindex msmall-model |
| Use the small address space model. This can produce smaller code, but |
| it does assume that all symbolic values and addresses fit into a |
| 20-bit range. |
| |
| @item -mno-lsim |
| @opindex mno-lsim |
| Assume that runtime support has been provided and so there is no need |
| to include the simulator library (@file{libsim.a}) on the linker |
| command line. |
| |
| @end table |
| |
| @node FRV Options |
| @subsection FRV Options |
| @cindex FRV Options |
| |
| @table @gcctabopt |
| @item -mgpr-32 |
| @opindex mgpr-32 |
| |
| Only use the first 32 general-purpose registers. |
| |
| @item -mgpr-64 |
| @opindex mgpr-64 |
| |
| Use all 64 general-purpose registers. |
| |
| @item -mfpr-32 |
| @opindex mfpr-32 |
| |
| Use only the first 32 floating-point registers. |
| |
| @item -mfpr-64 |
| @opindex mfpr-64 |
| |
| Use all 64 floating-point registers. |
| |
| @item -mhard-float |
| @opindex mhard-float |
| |
| Use hardware instructions for floating-point operations. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| |
| Use library routines for floating-point operations. |
| |
| @item -malloc-cc |
| @opindex malloc-cc |
| |
| Dynamically allocate condition code registers. |
| |
| @item -mfixed-cc |
| @opindex mfixed-cc |
| |
| Do not try to dynamically allocate condition code registers, only |
| use @code{icc0} and @code{fcc0}. |
| |
| @item -mdword |
| @opindex mdword |
| |
| Change ABI to use double word insns. |
| |
| @item -mno-dword |
| @opindex mno-dword |
| |
| Do not use double word instructions. |
| |
| @item -mdouble |
| @opindex mdouble |
| |
| Use floating-point double instructions. |
| |
| @item -mno-double |
| @opindex mno-double |
| |
| Do not use floating-point double instructions. |
| |
| @item -mmedia |
| @opindex mmedia |
| |
| Use media instructions. |
| |
| @item -mno-media |
| @opindex mno-media |
| |
| Do not use media instructions. |
| |
| @item -mmuladd |
| @opindex mmuladd |
| |
| Use multiply and add/subtract instructions. |
| |
| @item -mno-muladd |
| @opindex mno-muladd |
| |
| Do not use multiply and add/subtract instructions. |
| |
| @item -mfdpic |
| @opindex mfdpic |
| |
| Select the FDPIC ABI, which uses function descriptors to represent |
| pointers to functions. Without any PIC/PIE-related options, it |
| implies @option{-fPIE}. With @option{-fpic} or @option{-fpie}, it |
| assumes GOT entries and small data are within a 12-bit range from the |
| GOT base address; with @option{-fPIC} or @option{-fPIE}, GOT offsets |
| are computed with 32 bits. |
| With a @samp{bfin-elf} target, this option implies @option{-msim}. |
| |
| @item -minline-plt |
| @opindex minline-plt |
| |
| Enable inlining of PLT entries in function calls to functions that are |
| not known to bind locally. It has no effect without @option{-mfdpic}. |
| It's enabled by default if optimizing for speed and compiling for |
| shared libraries (i.e., @option{-fPIC} or @option{-fpic}), or when an |
| optimization option such as @option{-O3} or above is present in the |
| command line. |
| |
| @item -mTLS |
| @opindex mTLS |
| |
| Assume a large TLS segment when generating thread-local code. |
| |
| @item -mtls |
| @opindex mtls |
| |
| Do not assume a large TLS segment when generating thread-local code. |
| |
| @item -mgprel-ro |
| @opindex mgprel-ro |
| |
| Enable the use of @code{GPREL} relocations in the FDPIC ABI for data |
| that is known to be in read-only sections. It's enabled by default, |
| except for @option{-fpic} or @option{-fpie}: even though it may help |
| make the global offset table smaller, it trades 1 instruction for 4. |
| With @option{-fPIC} or @option{-fPIE}, it trades 3 instructions for 4, |
| one of which may be shared by multiple symbols, and it avoids the need |
| for a GOT entry for the referenced symbol, so it's more likely to be a |
| win. If it is not, @option{-mno-gprel-ro} can be used to disable it. |
| |
| @item -multilib-library-pic |
| @opindex multilib-library-pic |
| |
| Link with the (library, not FD) pic libraries. It's implied by |
| @option{-mlibrary-pic}, as well as by @option{-fPIC} and |
| @option{-fpic} without @option{-mfdpic}. You should never have to use |
| it explicitly. |
| |
| @item -mlinked-fp |
| @opindex mlinked-fp |
| |
| Follow the EABI requirement of always creating a frame pointer whenever |
| a stack frame is allocated. This option is enabled by default and can |
| be disabled with @option{-mno-linked-fp}. |
| |
| @item -mlong-calls |
| @opindex mlong-calls |
| |
| Use indirect addressing to call functions outside the current |
| compilation unit. This allows the functions to be placed anywhere |
| within the 32-bit address space. |
| |
| @item -malign-labels |
| @opindex malign-labels |
| |
| Try to align labels to an 8-byte boundary by inserting NOPs into the |
| previous packet. This option only has an effect when VLIW packing |
| is enabled. It doesn't create new packets; it merely adds NOPs to |
| existing ones. |
| |
| @item -mlibrary-pic |
| @opindex mlibrary-pic |
| |
| Generate position-independent EABI code. |
| |
| @item -macc-4 |
| @opindex macc-4 |
| |
| Use only the first four media accumulator registers. |
| |
| @item -macc-8 |
| @opindex macc-8 |
| |
| Use all eight media accumulator registers. |
| |
| @item -mpack |
| @opindex mpack |
| |
| Pack VLIW instructions. |
| |
| @item -mno-pack |
| @opindex mno-pack |
| |
| Do not pack VLIW instructions. |
| |
| @item -mno-eflags |
| @opindex mno-eflags |
| |
| Do not mark ABI switches in e_flags. |
| |
| @item -mcond-move |
| @opindex mcond-move |
| |
| Enable the use of conditional-move instructions (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-cond-move |
| @opindex mno-cond-move |
| |
| Disable the use of conditional-move instructions. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mscc |
| @opindex mscc |
| |
| Enable the use of conditional set instructions (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-scc |
| @opindex mno-scc |
| |
| Disable the use of conditional set instructions. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mcond-exec |
| @opindex mcond-exec |
| |
| Enable the use of conditional execution (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-cond-exec |
| @opindex mno-cond-exec |
| |
| Disable the use of conditional execution. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mvliw-branch |
| @opindex mvliw-branch |
| |
| Run a pass to pack branches into VLIW instructions (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-vliw-branch |
| @opindex mno-vliw-branch |
| |
| Do not run a pass to pack branches into VLIW instructions. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mmulti-cond-exec |
| @opindex mmulti-cond-exec |
| |
| Enable optimization of @code{&&} and @code{||} in conditional execution |
| (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-multi-cond-exec |
| @opindex mno-multi-cond-exec |
| |
| Disable optimization of @code{&&} and @code{||} in conditional execution. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mnested-cond-exec |
| @opindex mnested-cond-exec |
| |
| Enable nested conditional execution optimizations (default). |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -mno-nested-cond-exec |
| @opindex mno-nested-cond-exec |
| |
| Disable nested conditional execution optimizations. |
| |
| This switch is mainly for debugging the compiler and will likely be removed |
| in a future version. |
| |
| @item -moptimize-membar |
| @opindex moptimize-membar |
| |
| This switch removes redundant @code{membar} instructions from the |
| compiler-generated code. It is enabled by default. |
| |
| @item -mno-optimize-membar |
| @opindex mno-optimize-membar |
| |
| This switch disables the automatic removal of redundant @code{membar} |
| instructions from the generated code. |
| |
| @item -mtomcat-stats |
| @opindex mtomcat-stats |
| |
| Cause gas to print out tomcat statistics. |
| |
| @item -mcpu=@var{cpu} |
| @opindex mcpu |
| |
| Select the processor type for which to generate code. Possible values are |
| @samp{frv}, @samp{fr550}, @samp{tomcat}, @samp{fr500}, @samp{fr450}, |
| @samp{fr405}, @samp{fr400}, @samp{fr300} and @samp{simple}. |
| |
| @end table |
| |
| @node GNU/Linux Options |
| @subsection GNU/Linux Options |
| |
| These @samp{-m} options are defined for GNU/Linux targets: |
| |
| @table @gcctabopt |
| @item -mglibc |
| @opindex mglibc |
| Use the GNU C library. This is the default except |
| on @samp{*-*-linux-*uclibc*} and @samp{*-*-linux-*android*} targets. |
| |
| @item -muclibc |
| @opindex muclibc |
| Use uClibc C library. This is the default on |
| @samp{*-*-linux-*uclibc*} targets. |
| |
| @item -mbionic |
| @opindex mbionic |
| Use Bionic C library. This is the default on |
| @samp{*-*-linux-*android*} targets. |
| |
| @item -mandroid |
| @opindex mandroid |
| Compile code compatible with Android platform. This is the default on |
| @samp{*-*-linux-*android*} targets. |
| |
| When compiling, this option enables @option{-mbionic}, @option{-fPIC}, |
| @option{-fno-exceptions} and @option{-fno-rtti} by default. When linking, |
| this option makes the GCC driver pass Android-specific options to the linker. |
| Finally, this option causes the preprocessor macro @code{__ANDROID__} |
| to be defined. |
| |
| @item -tno-android-cc |
| @opindex tno-android-cc |
| Disable compilation effects of @option{-mandroid}, i.e., do not enable |
| @option{-mbionic}, @option{-fPIC}, @option{-fno-exceptions} and |
| @option{-fno-rtti} by default. |
| |
| @item -tno-android-ld |
| @opindex tno-android-ld |
| Disable linking effects of @option{-mandroid}, i.e., pass standard Linux |
| linking options to the linker. |
| |
| @end table |
| |
| @node H8/300 Options |
| @subsection H8/300 Options |
| |
| These @samp{-m} options are defined for the H8/300 implementations: |
| |
| @table @gcctabopt |
| @item -mrelax |
| @opindex mrelax |
| Shorten some address references at link time, when possible; uses the |
| linker option @option{-relax}. @xref{H8/300,, @code{ld} and the H8/300, |
| ld, Using ld}, for a fuller description. |
| |
| @item -mh |
| @opindex mh |
| Generate code for the H8/300H@. |
| |
| @item -ms |
| @opindex ms |
| Generate code for the H8S@. |
| |
| @item -mn |
| @opindex mn |
| Generate code for the H8S and H8/300H in the normal mode. This switch |
| must be used either with @option{-mh} or @option{-ms}. |
| |
| @item -ms2600 |
| @opindex ms2600 |
| Generate code for the H8S/2600. This switch must be used with @option{-ms}. |
| |
| @item -mexr |
| @opindex mexr |
| Extended registers are stored on stack before execution of function |
| with monitor attribute. Default option is @option{-mexr}. |
| This option is valid only for H8S targets. |
| |
| @item -mno-exr |
| @opindex mno-exr |
| Extended registers are not stored on stack before execution of function |
| with monitor attribute. Default option is @option{-mno-exr}. |
| This option is valid only for H8S targets. |
| |
| @item -mint32 |
| @opindex mint32 |
| Make @code{int} data 32 bits by default. |
| |
| @item -malign-300 |
| @opindex malign-300 |
| On the H8/300H and H8S, use the same alignment rules as for the H8/300. |
| The default for the H8/300H and H8S is to align longs and floats on |
| 4-byte boundaries. |
| @option{-malign-300} causes them to be aligned on 2-byte boundaries. |
| This option has no effect on the H8/300. |
| @end table |
| |
| @node HPPA Options |
| @subsection HPPA Options |
| @cindex HPPA Options |
| |
| These @samp{-m} options are defined for the HPPA family of computers: |
| |
| @table @gcctabopt |
| @item -march=@var{architecture-type} |
| @opindex march |
| Generate code for the specified architecture. The choices for |
| @var{architecture-type} are @samp{1.0} for PA 1.0, @samp{1.1} for PA |
| 1.1, and @samp{2.0} for PA 2.0 processors. Refer to |
| @file{/usr/lib/sched.models} on an HP-UX system to determine the proper |
| architecture option for your machine. Code compiled for lower numbered |
| architectures runs on higher numbered architectures, but not the |
| other way around. |
| |
| @item -mpa-risc-1-0 |
| @itemx -mpa-risc-1-1 |
| @itemx -mpa-risc-2-0 |
| @opindex mpa-risc-1-0 |
| @opindex mpa-risc-1-1 |
| @opindex mpa-risc-2-0 |
| Synonyms for @option{-march=1.0}, @option{-march=1.1}, and @option{-march=2.0} respectively. |
| |
| @item -mbig-switch |
| @opindex mbig-switch |
| Generate code suitable for big switch tables. Use this option only if |
| the assembler/linker complain about out-of-range branches within a switch |
| table. |
| |
| @item -mjump-in-delay |
| @opindex mjump-in-delay |
| Fill delay slots of function calls with unconditional jump instructions |
| by modifying the return pointer for the function call to be the target |
| of the conditional jump. |
| |
| @item -mdisable-fpregs |
| @opindex mdisable-fpregs |
| Prevent floating-point registers from being used in any manner. This is |
| necessary for compiling kernels that perform lazy context switching of |
| floating-point registers. If you use this option and attempt to perform |
| floating-point operations, the compiler aborts. |
| |
| @item -mdisable-indexing |
| @opindex mdisable-indexing |
| Prevent the compiler from using indexing address modes. This avoids some |
| rather obscure problems when compiling MIG generated code under MACH@. |
| |
| @item -mno-space-regs |
| @opindex mno-space-regs |
| Generate code that assumes the target has no space registers. This allows |
| GCC to generate faster indirect calls and use unscaled index address modes. |
| |
| Such code is suitable for level 0 PA systems and kernels. |
| |
| @item -mfast-indirect-calls |
| @opindex mfast-indirect-calls |
| Generate code that assumes calls never cross space boundaries. This |
| allows GCC to emit code that performs faster indirect calls. |
| |
| This option does not work in the presence of shared libraries or nested |
| functions. |
| |
| @item -mfixed-range=@var{register-range} |
| @opindex mfixed-range |
| Generate code treating the given register range as fixed registers. |
| A fixed register is one that the register allocator cannot use. This is |
| useful when compiling kernel code. A register range is specified as |
| two registers separated by a dash. Multiple register ranges can be |
| specified separated by a comma. |
| |
| @item -mlong-load-store |
| @opindex mlong-load-store |
| Generate 3-instruction load and store sequences as sometimes required by |
| the HP-UX 10 linker. This is equivalent to the @samp{+k} option to |
| the HP compilers. |
| |
| @item -mportable-runtime |
| @opindex mportable-runtime |
| Use the portable calling conventions proposed by HP for ELF systems. |
| |
| @item -mgas |
| @opindex mgas |
| Enable the use of assembler directives only GAS understands. |
| |
| @item -mschedule=@var{cpu-type} |
| @opindex mschedule |
| Schedule code according to the constraints for the machine type |
| @var{cpu-type}. The choices for @var{cpu-type} are @samp{700} |
| @samp{7100}, @samp{7100LC}, @samp{7200}, @samp{7300} and @samp{8000}. Refer |
| to @file{/usr/lib/sched.models} on an HP-UX system to determine the |
| proper scheduling option for your machine. The default scheduling is |
| @samp{8000}. |
| |
| @item -mlinker-opt |
| @opindex mlinker-opt |
| Enable the optimization pass in the HP-UX linker. Note this makes symbolic |
| debugging impossible. It also triggers a bug in the HP-UX 8 and HP-UX 9 |
| linkers in which they give bogus error messages when linking some programs. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Generate output containing library calls for floating point. |
| @strong{Warning:} the requisite libraries are not available for all HPPA |
| targets. Normally the facilities of the machine's usual C compiler are |
| used, but this cannot be done directly in cross-compilation. You must make |
| your own arrangements to provide suitable library functions for |
| cross-compilation. |
| |
| @option{-msoft-float} changes the calling convention in the output file; |
| therefore, it is only useful if you compile @emph{all} of a program with |
| this option. In particular, you need to compile @file{libgcc.a}, the |
| library that comes with GCC, with @option{-msoft-float} in order for |
| this to work. |
| |
| @item -msio |
| @opindex msio |
| Generate the predefine, @code{_SIO}, for server IO@. The default is |
| @option{-mwsio}. This generates the predefines, @code{__hp9000s700}, |
| @code{__hp9000s700__} and @code{_WSIO}, for workstation IO@. These |
| options are available under HP-UX and HI-UX@. |
| |
| @item -mgnu-ld |
| @opindex mgnu-ld |
| Use options specific to GNU @command{ld}. |
| This passes @option{-shared} to @command{ld} when |
| building a shared library. It is the default when GCC is configured, |
| explicitly or implicitly, with the GNU linker. This option does not |
| affect which @command{ld} is called; it only changes what parameters |
| are passed to that @command{ld}. |
| The @command{ld} that is called is determined by the |
| @option{--with-ld} configure option, GCC's program search path, and |
| finally by the user's @env{PATH}. The linker used by GCC can be printed |
| using @samp{which `gcc -print-prog-name=ld`}. This option is only available |
| on the 64-bit HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. |
| |
| @item -mhp-ld |
| @opindex mhp-ld |
| Use options specific to HP @command{ld}. |
| This passes @option{-b} to @command{ld} when building |
| a shared library and passes @option{+Accept TypeMismatch} to @command{ld} on all |
| links. It is the default when GCC is configured, explicitly or |
| implicitly, with the HP linker. This option does not affect |
| which @command{ld} is called; it only changes what parameters are passed to that |
| @command{ld}. |
| The @command{ld} that is called is determined by the @option{--with-ld} |
| configure option, GCC's program search path, and finally by the user's |
| @env{PATH}. The linker used by GCC can be printed using @samp{which |
| `gcc -print-prog-name=ld`}. This option is only available on the 64-bit |
| HP-UX GCC, i.e.@: configured with @samp{hppa*64*-*-hpux*}. |
| |
| @item -mlong-calls |
| @opindex mno-long-calls |
| Generate code that uses long call sequences. This ensures that a call |
| is always able to reach linker generated stubs. The default is to generate |
| long calls only when the distance from the call site to the beginning |
| of the function or translation unit, as the case may be, exceeds a |
| predefined limit set by the branch type being used. The limits for |
| normal calls are 7,600,000 and 240,000 bytes, respectively for the |
| PA 2.0 and PA 1.X architectures. Sibcalls are always limited at |
| 240,000 bytes. |
| |
| Distances are measured from the beginning of functions when using the |
| @option{-ffunction-sections} option, or when using the @option{-mgas} |
| and @option{-mno-portable-runtime} options together under HP-UX with |
| the SOM linker. |
| |
| It is normally not desirable to use this option as it degrades |
| performance. However, it may be useful in large applications, |
| particularly when partial linking is used to build the application. |
| |
| The types of long calls used depends on the capabilities of the |
| assembler and linker, and the type of code being generated. The |
| impact on systems that support long absolute calls, and long pic |
| symbol-difference or pc-relative calls should be relatively small. |
| However, an indirect call is used on 32-bit ELF systems in pic code |
| and it is quite long. |
| |
| @item -munix=@var{unix-std} |
| @opindex march |
| Generate compiler predefines and select a startfile for the specified |
| UNIX standard. The choices for @var{unix-std} are @samp{93}, @samp{95} |
| and @samp{98}. @samp{93} is supported on all HP-UX versions. @samp{95} |
| is available on HP-UX 10.10 and later. @samp{98} is available on HP-UX |
| 11.11 and later. The default values are @samp{93} for HP-UX 10.00, |
| @samp{95} for HP-UX 10.10 though to 11.00, and @samp{98} for HP-UX 11.11 |
| and later. |
| |
| @option{-munix=93} provides the same predefines as GCC 3.3 and 3.4. |
| @option{-munix=95} provides additional predefines for @code{XOPEN_UNIX} |
| and @code{_XOPEN_SOURCE_EXTENDED}, and the startfile @file{unix95.o}. |
| @option{-munix=98} provides additional predefines for @code{_XOPEN_UNIX}, |
| @code{_XOPEN_SOURCE_EXTENDED}, @code{_INCLUDE__STDC_A1_SOURCE} and |
| @code{_INCLUDE_XOPEN_SOURCE_500}, and the startfile @file{unix98.o}. |
| |
| It is @emph{important} to note that this option changes the interfaces |
| for various library routines. It also affects the operational behavior |
| of the C library. Thus, @emph{extreme} care is needed in using this |
| option. |
| |
| Library code that is intended to operate with more than one UNIX |
| standard must test, set and restore the variable @var{__xpg4_extended_mask} |
| as appropriate. Most GNU software doesn't provide this capability. |
| |
| @item -nolibdld |
| @opindex nolibdld |
| Suppress the generation of link options to search libdld.sl when the |
| @option{-static} option is specified on HP-UX 10 and later. |
| |
| @item -static |
| @opindex static |
| The HP-UX implementation of setlocale in libc has a dependency on |
| libdld.sl. There isn't an archive version of libdld.sl. Thus, |
| when the @option{-static} option is specified, special link options |
| are needed to resolve this dependency. |
| |
| On HP-UX 10 and later, the GCC driver adds the necessary options to |
| link with libdld.sl when the @option{-static} option is specified. |
| This causes the resulting binary to be dynamic. On the 64-bit port, |
| the linkers generate dynamic binaries by default in any case. The |
| @option{-nolibdld} option can be used to prevent the GCC driver from |
| adding these link options. |
| |
| @item -threads |
| @opindex threads |
| Add support for multithreading with the @dfn{dce thread} library |
| under HP-UX@. This option sets flags for both the preprocessor and |
| linker. |
| @end table |
| |
| @node i386 and x86-64 Options |
| @subsection Intel 386 and AMD x86-64 Options |
| @cindex i386 Options |
| @cindex x86-64 Options |
| @cindex Intel 386 Options |
| @cindex AMD x86-64 Options |
| |
| These @samp{-m} options are defined for the i386 and x86-64 family of |
| computers: |
| |
| @table @gcctabopt |
| |
| @item -march=@var{cpu-type} |
| @opindex march |
| Generate instructions for the machine type @var{cpu-type}. In contrast to |
| @option{-mtune=@var{cpu-type}}, which merely tunes the generated code |
| for the specified @var{cpu-type}, @option{-march=@var{cpu-type}} allows GCC |
| to generate code that may not run at all on processors other than the one |
| indicated. Specifying @option{-march=@var{cpu-type}} implies |
| @option{-mtune=@var{cpu-type}}. |
| |
| The choices for @var{cpu-type} are: |
| |
| @table @samp |
| @item native |
| This selects the CPU to generate code for at compilation time by determining |
| the processor type of the compiling machine. Using @option{-march=native} |
| enables all instruction subsets supported by the local machine (hence |
| the result might not run on different machines). Using @option{-mtune=native} |
| produces code optimized for the local machine under the constraints |
| of the selected instruction set. |
| |
| @item i386 |
| Original Intel i386 CPU@. |
| |
| @item i486 |
| Intel i486 CPU@. (No scheduling is implemented for this chip.) |
| |
| @item i586 |
| @itemx pentium |
| Intel Pentium CPU with no MMX support. |
| |
| @item pentium-mmx |
| Intel Pentium MMX CPU, based on Pentium core with MMX instruction set support. |
| |
| @item pentiumpro |
| Intel Pentium Pro CPU@. |
| |
| @item i686 |
| When used with @option{-march}, the Pentium Pro |
| instruction set is used, so the code runs on all i686 family chips. |
| When used with @option{-mtune}, it has the same meaning as @samp{generic}. |
| |
| @item pentium2 |
| Intel Pentium II CPU, based on Pentium Pro core with MMX instruction set |
| support. |
| |
| @item pentium3 |
| @itemx pentium3m |
| Intel Pentium III CPU, based on Pentium Pro core with MMX and SSE instruction |
| set support. |
| |
| @item pentium-m |
| Intel Pentium M; low-power version of Intel Pentium III CPU |
| with MMX, SSE and SSE2 instruction set support. Used by Centrino notebooks. |
| |
| @item pentium4 |
| @itemx pentium4m |
| Intel Pentium 4 CPU with MMX, SSE and SSE2 instruction set support. |
| |
| @item prescott |
| Improved version of Intel Pentium 4 CPU with MMX, SSE, SSE2 and SSE3 instruction |
| set support. |
| |
| @item nocona |
| Improved version of Intel Pentium 4 CPU with 64-bit extensions, MMX, SSE, |
| SSE2 and SSE3 instruction set support. |
| |
| @item core2 |
| Intel Core 2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 |
| instruction set support. |
| |
| @item corei7 |
| Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, SSE4.1 |
| and SSE4.2 instruction set support. |
| |
| @item corei7-avx |
| Intel Core i7 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, |
| SSE4.1, SSE4.2, AVX, AES and PCLMUL instruction set support. |
| |
| @item core-avx-i |
| Intel Core CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3, SSSE3, |
| SSE4.1, SSE4.2, AVX, AES, PCLMUL, FSGSBASE, RDRND and F16C instruction |
| set support. |
| |
| @item atom |
| Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3 |
| instruction set support. |
| |
| @item k6 |
| AMD K6 CPU with MMX instruction set support. |
| |
| @item k6-2 |
| @itemx k6-3 |
| Improved versions of AMD K6 CPU with MMX and 3DNow!@: instruction set support. |
| |
| @item athlon |
| @itemx athlon-tbird |
| AMD Athlon CPU with MMX, 3dNOW!, enhanced 3DNow!@: and SSE prefetch instructions |
| support. |
| |
| @item athlon-4 |
| @itemx athlon-xp |
| @itemx athlon-mp |
| Improved AMD Athlon CPU with MMX, 3DNow!, enhanced 3DNow!@: and full SSE |
| instruction set support. |
| |
| @item k8 |
| @itemx opteron |
| @itemx athlon64 |
| @itemx athlon-fx |
| Processors based on the AMD K8 core with x86-64 instruction set support, |
| including the AMD Opteron, Athlon 64, and Athlon 64 FX processors. |
| (This supersets MMX, SSE, SSE2, 3DNow!, enhanced 3DNow!@: and 64-bit |
| instruction set extensions.) |
| |
| @item k8-sse3 |
| @itemx opteron-sse3 |
| @itemx athlon64-sse3 |
| Improved versions of AMD K8 cores with SSE3 instruction set support. |
| |
| @item amdfam10 |
| @itemx barcelona |
| CPUs based on AMD Family 10h cores with x86-64 instruction set support. (This |
| supersets MMX, SSE, SSE2, SSE3, SSE4A, 3DNow!, enhanced 3DNow!, ABM and 64-bit |
| instruction set extensions.) |
| |
| @item bdver1 |
| CPUs based on AMD Family 15h cores with x86-64 instruction set support. (This |
| supersets FMA4, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, SSE2, SSE3, SSE4A, |
| SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set extensions.) |
| @item bdver2 |
| AMD Family 15h core based CPUs with x86-64 instruction set support. (This |
| supersets BMI, TBM, F16C, FMA, AVX, XOP, LWP, AES, PCL_MUL, CX16, MMX, SSE, |
| SSE2, SSE3, SSE4A, SSSE3, SSE4.1, SSE4.2, ABM and 64-bit instruction set |
| extensions.) |
| |
| @item btver1 |
| CPUs based on AMD Family 14h cores with x86-64 instruction set support. (This |
| supersets MMX, SSE, SSE2, SSE3, SSSE3, SSE4A, CX16, ABM and 64-bit |
| instruction set extensions.) |
| |
| @item btver2 |
| CPUs based on AMD Family 16h cores with x86-64 instruction set support. This |
| includes MOVBE, F16C, BMI, AVX, PCL_MUL, AES, SSE4.2, SSE4.1, CX16, ABM, |
| SSE4A, SSSE3, SSE3, SSE2, SSE, MMX and 64-bit instruction set extensions. |
| |
| @item winchip-c6 |
| IDT WinChip C6 CPU, dealt in same way as i486 with additional MMX instruction |
| set support. |
| |
| @item winchip2 |
| IDT WinChip 2 CPU, dealt in same way as i486 with additional MMX and 3DNow!@: |
| instruction set support. |
| |
| @item c3 |
| VIA C3 CPU with MMX and 3DNow!@: instruction set support. (No scheduling is |
| implemented for this chip.) |
| |
| @item c3-2 |
| VIA C3-2 (Nehemiah/C5XL) CPU with MMX and SSE instruction set support. |
| (No scheduling is |
| implemented for this chip.) |
| |
| @item geode |
| AMD Geode embedded processor with MMX and 3DNow!@: instruction set support. |
| @end table |
| |
| @item -mtune=@var{cpu-type} |
| @opindex mtune |
| Tune to @var{cpu-type} everything applicable about the generated code, except |
| for the ABI and the set of available instructions. |
| While picking a specific @var{cpu-type} schedules things appropriately |
| for that particular chip, the compiler does not generate any code that |
| cannot run on the default machine type unless you use a |
| @option{-march=@var{cpu-type}} option. |
| For example, if GCC is configured for i686-pc-linux-gnu |
| then @option{-mtune=pentium4} generates code that is tuned for Pentium 4 |
| but still runs on i686 machines. |
| |
| The choices for @var{cpu-type} are the same as for @option{-march}. |
| In addition, @option{-mtune} supports an extra choice for @var{cpu-type}: |
| |
| @table @samp |
| @item generic |
| Produce code optimized for the most common IA32/@/AMD64/@/EM64T processors. |
| If you know the CPU on which your code will run, then you should use |
| the corresponding @option{-mtune} or @option{-march} option instead of |
| @option{-mtune=generic}. But, if you do not know exactly what CPU users |
| of your application will have, then you should use this option. |
| |
| As new processors are deployed in the marketplace, the behavior of this |
| option will change. Therefore, if you upgrade to a newer version of |
| GCC, code generation controlled by this option will change to reflect |
| the processors |
| that are most common at the time that version of GCC is released. |
| |
| There is no @option{-march=generic} option because @option{-march} |
| indicates the instruction set the compiler can use, and there is no |
| generic instruction set applicable to all processors. In contrast, |
| @option{-mtune} indicates the processor (or, in this case, collection of |
| processors) for which the code is optimized. |
| @end table |
| |
| @item -mcpu=@var{cpu-type} |
| @opindex mcpu |
| A deprecated synonym for @option{-mtune}. |
| |
| @item -mfpmath=@var{unit} |
| @opindex mfpmath |
| Generate floating-point arithmetic for selected unit @var{unit}. The choices |
| for @var{unit} are: |
| |
| @table @samp |
| @item 387 |
| Use the standard 387 floating-point coprocessor present on the majority of chips and |
| emulated otherwise. Code compiled with this option runs almost everywhere. |
| The temporary results are computed in 80-bit precision instead of the precision |
| specified by the type, resulting in slightly different results compared to most |
| of other chips. See @option{-ffloat-store} for more detailed description. |
| |
| This is the default choice for i386 compiler. |
| |
| @item sse |
| Use scalar floating-point instructions present in the SSE instruction set. |
| This instruction set is supported by Pentium III and newer chips, |
| and in the AMD line |
| by Athlon-4, Athlon XP and Athlon MP chips. The earlier version of the SSE |
| instruction set supports only single-precision arithmetic, thus the double and |
| extended-precision arithmetic are still done using 387. A later version, present |
| only in Pentium 4 and AMD x86-64 chips, supports double-precision |
| arithmetic too. |
| |
| For the i386 compiler, you must use @option{-march=@var{cpu-type}}, @option{-msse} |
| or @option{-msse2} switches to enable SSE extensions and make this option |
| effective. For the x86-64 compiler, these extensions are enabled by default. |
| |
| The resulting code should be considerably faster in the majority of cases and avoid |
| the numerical instability problems of 387 code, but may break some existing |
| code that expects temporaries to be 80 bits. |
| |
| This is the default choice for the x86-64 compiler. |
| |
| @item sse,387 |
| @itemx sse+387 |
| @itemx both |
| Attempt to utilize both instruction sets at once. This effectively doubles the |
| amount of available registers, and on chips with separate execution units for |
| 387 and SSE the execution resources too. Use this option with care, as it is |
| still experimental, because the GCC register allocator does not model separate |
| functional units well, resulting in unstable performance. |
| @end table |
| |
| @item -masm=@var{dialect} |
| @opindex masm=@var{dialect} |
| Output assembly instructions using selected @var{dialect}. Supported |
| choices are @samp{intel} or @samp{att} (the default). Darwin does |
| not support @samp{intel}. |
| |
| @item -mieee-fp |
| @itemx -mno-ieee-fp |
| @opindex mieee-fp |
| @opindex mno-ieee-fp |
| Control whether or not the compiler uses IEEE floating-point |
| comparisons. These correctly handle the case where the result of a |
| comparison is unordered. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Generate output containing library calls for floating point. |
| |
| @strong{Warning:} the requisite libraries are not part of GCC@. |
| Normally the facilities of the machine's usual C compiler are used, but |
| this can't be done directly in cross-compilation. You must make your |
| own arrangements to provide suitable library functions for |
| cross-compilation. |
| |
| On machines where a function returns floating-point results in the 80387 |
| register stack, some floating-point opcodes may be emitted even if |
| @option{-msoft-float} is used. |
| |
| @item -mno-fp-ret-in-387 |
| @opindex mno-fp-ret-in-387 |
| Do not use the FPU registers for return values of functions. |
| |
| The usual calling convention has functions return values of types |
| @code{float} and @code{double} in an FPU register, even if there |
| is no FPU@. The idea is that the operating system should emulate |
| an FPU@. |
| |
| The option @option{-mno-fp-ret-in-387} causes such values to be returned |
| in ordinary CPU registers instead. |
| |
| @item -mno-fancy-math-387 |
| @opindex mno-fancy-math-387 |
| Some 387 emulators do not support the @code{sin}, @code{cos} and |
| @code{sqrt} instructions for the 387. Specify this option to avoid |
| generating those instructions. This option is the default on FreeBSD, |
| OpenBSD and NetBSD@. This option is overridden when @option{-march} |
| indicates that the target CPU always has an FPU and so the |
| instruction does not need emulation. These |
| instructions are not generated unless you also use the |
| @option{-funsafe-math-optimizations} switch. |
| |
| @item -malign-double |
| @itemx -mno-align-double |
| @opindex malign-double |
| @opindex mno-align-double |
| Control whether GCC aligns @code{double}, @code{long double}, and |
| @code{long long} variables on a two-word boundary or a one-word |
| boundary. Aligning @code{double} variables on a two-word boundary |
| produces code that runs somewhat faster on a Pentium at the |
| expense of more memory. |
| |
| On x86-64, @option{-malign-double} is enabled by default. |
| |
| @strong{Warning:} if you use the @option{-malign-double} switch, |
| structures containing the above types are aligned differently than |
| the published application binary interface specifications for the 386 |
| and are not binary compatible with structures in code compiled |
| without that switch. |
| |
| @item -m96bit-long-double |
| @itemx -m128bit-long-double |
| @opindex m96bit-long-double |
| @opindex m128bit-long-double |
| These switches control the size of @code{long double} type. The i386 |
| application binary interface specifies the size to be 96 bits, |
| so @option{-m96bit-long-double} is the default in 32-bit mode. |
| |
| Modern architectures (Pentium and newer) prefer @code{long double} |
| to be aligned to an 8- or 16-byte boundary. In arrays or structures |
| conforming to the ABI, this is not possible. So specifying |
| @option{-m128bit-long-double} aligns @code{long double} |
| to a 16-byte boundary by padding the @code{long double} with an additional |
| 32-bit zero. |
| |
| In the x86-64 compiler, @option{-m128bit-long-double} is the default choice as |
| its ABI specifies that @code{long double} is aligned on 16-byte boundary. |
| |
| Notice that neither of these options enable any extra precision over the x87 |
| standard of 80 bits for a @code{long double}. |
| |
| @strong{Warning:} if you override the default value for your target ABI, this |
| changes the size of |
| structures and arrays containing @code{long double} variables, |
| as well as modifying the function calling convention for functions taking |
| @code{long double}. Hence they are not binary-compatible |
| with code compiled without that switch. |
| |
| @item -mlong-double-64 |
| @itemx -mlong-double-80 |
| @opindex mlong-double-64 |
| @opindex mlong-double-80 |
| These switches control the size of @code{long double} type. A size |
| of 64 bits makes the @code{long double} type equivalent to the @code{double} |
| type. This is the default for Bionic C library. |
| |
| @strong{Warning:} if you override the default value for your target ABI, this |
| changes the size of |
| structures and arrays containing @code{long double} variables, |
| as well as modifying the function calling convention for functions taking |
| @code{long double}. Hence they are not binary-compatible |
| with code compiled without that switch. |
| |
| @item -mlarge-data-threshold=@var{threshold} |
| @opindex mlarge-data-threshold |
| When @option{-mcmodel=medium} is specified, data objects larger than |
| @var{threshold} are placed in the large data section. This value must be the |
| same across all objects linked into the binary, and defaults to 65535. |
| |
| @item -mrtd |
| @opindex mrtd |
| Use a different function-calling convention, in which functions that |
| take a fixed number of arguments return with the @code{ret @var{num}} |
| instruction, which pops their arguments while returning. This saves one |
| instruction in the caller since there is no need to pop the arguments |
| there. |
| |
| You can specify that an individual function is called with this calling |
| sequence with the function attribute @samp{stdcall}. You can also |
| override the @option{-mrtd} option by using the function attribute |
| @samp{cdecl}. @xref{Function Attributes}. |
| |
| @strong{Warning:} this calling convention is incompatible with the one |
| normally used on Unix, so you cannot use it if you need to call |
| libraries compiled with the Unix compiler. |
| |
| Also, you must provide function prototypes for all functions that |
| take variable numbers of arguments (including @code{printf}); |
| otherwise incorrect code is generated for calls to those |
| functions. |
| |
| In addition, seriously incorrect code results if you call a |
| function with too many arguments. (Normally, extra arguments are |
| harmlessly ignored.) |
| |
| @item -mregparm=@var{num} |
| @opindex mregparm |
| Control how many registers are used to pass integer arguments. By |
| default, no registers are used to pass arguments, and at most 3 |
| registers can be used. You can control this behavior for a specific |
| function by using the function attribute @samp{regparm}. |
| @xref{Function Attributes}. |
| |
| @strong{Warning:} if you use this switch, and |
| @var{num} is nonzero, then you must build all modules with the same |
| value, including any libraries. This includes the system libraries and |
| startup modules. |
| |
| @item -msseregparm |
| @opindex msseregparm |
| Use SSE register passing conventions for float and double arguments |
| and return values. You can control this behavior for a specific |
| function by using the function attribute @samp{sseregparm}. |
| @xref{Function Attributes}. |
| |
| @strong{Warning:} if you use this switch then you must build all |
| modules with the same value, including any libraries. This includes |
| the system libraries and startup modules. |
| |
| @item -mvect8-ret-in-mem |
| @opindex mvect8-ret-in-mem |
| Return 8-byte vectors in memory instead of MMX registers. This is the |
| default on Solaris@tie{}8 and 9 and VxWorks to match the ABI of the Sun |
| Studio compilers until version 12. Later compiler versions (starting |
| with Studio 12 Update@tie{}1) follow the ABI used by other x86 targets, which |
| is the default on Solaris@tie{}10 and later. @emph{Only} use this option if |
| you need to remain compatible with existing code produced by those |
| previous compiler versions or older versions of GCC@. |
| |
| @item -mpc32 |
| @itemx -mpc64 |
| @itemx -mpc80 |
| @opindex mpc32 |
| @opindex mpc64 |
| @opindex mpc80 |
| |
| Set 80387 floating-point precision to 32, 64 or 80 bits. When @option{-mpc32} |
| is specified, the significands of results of floating-point operations are |
| rounded to 24 bits (single precision); @option{-mpc64} rounds the |
| significands of results of floating-point operations to 53 bits (double |
| precision) and @option{-mpc80} rounds the significands of results of |
| floating-point operations to 64 bits (extended double precision), which is |
| the default. When this option is used, floating-point operations in higher |
| precisions are not available to the programmer without setting the FPU |
| control word explicitly. |
| |
| Setting the rounding of floating-point operations to less than the default |
| 80 bits can speed some programs by 2% or more. Note that some mathematical |
| libraries assume that extended-precision (80-bit) floating-point operations |
| are enabled by default; routines in such libraries could suffer significant |
| loss of accuracy, typically through so-called ``catastrophic cancellation'', |
| when this option is used to set the precision to less than extended precision. |
| |
| @item -mstackrealign |
| @opindex mstackrealign |
| Realign the stack at entry. On the Intel x86, the @option{-mstackrealign} |
| option generates an alternate prologue and epilogue that realigns the |
| run-time stack if necessary. This supports mixing legacy codes that keep |
| 4-byte stack alignment with modern codes that keep 16-byte stack alignment for |
| SSE compatibility. See also the attribute @code{force_align_arg_pointer}, |
| applicable to individual functions. |
| |
| @item -mpreferred-stack-boundary=@var{num} |
| @opindex mpreferred-stack-boundary |
| Attempt to keep the stack boundary aligned to a 2 raised to @var{num} |
| byte boundary. If @option{-mpreferred-stack-boundary} is not specified, |
| the default is 4 (16 bytes or 128 bits). |
| |
| @strong{Warning:} When generating code for the x86-64 architecture with |
| SSE extensions disabled, @option{-mpreferred-stack-boundary=3} can be |
| used to keep the stack boundary aligned to 8 byte boundary. Since |
| x86-64 ABI require 16 byte stack alignment, this is ABI incompatible and |
| intended to be used in controlled environment where stack space is |
| important limitation. This option will lead to wrong code when functions |
| compiled with 16 byte stack alignment (such as functions from a standard |
| library) are called with misaligned stack. In this case, SSE |
| instructions may lead to misaligned memory access traps. In addition, |
| variable arguments will be handled incorrectly for 16 byte aligned |
| objects (including x87 long double and __int128), leading to wrong |
| results. You must build all modules with |
| @option{-mpreferred-stack-boundary=3}, including any libraries. This |
| includes the system libraries and startup modules. |
| |
| @item -mincoming-stack-boundary=@var{num} |
| @opindex mincoming-stack-boundary |
| Assume the incoming stack is aligned to a 2 raised to @var{num} byte |
| boundary. If @option{-mincoming-stack-boundary} is not specified, |
| the one specified by @option{-mpreferred-stack-boundary} is used. |
| |
| On Pentium and Pentium Pro, @code{double} and @code{long double} values |
| should be aligned to an 8-byte boundary (see @option{-malign-double}) or |
| suffer significant run time performance penalties. On Pentium III, the |
| Streaming SIMD Extension (SSE) data type @code{__m128} may not work |
| properly if it is not 16-byte aligned. |
| |
| To ensure proper alignment of this values on the stack, the stack boundary |
| must be as aligned as that required by any value stored on the stack. |
| Further, every function must be generated such that it keeps the stack |
| aligned. Thus calling a function compiled with a higher preferred |
| stack boundary from a function compiled with a lower preferred stack |
| boundary most likely misaligns the stack. It is recommended that |
| libraries that use callbacks always use the default setting. |
| |
| This extra alignment does consume extra stack space, and generally |
| increases code size. Code that is sensitive to stack space usage, such |
| as embedded systems and operating system kernels, may want to reduce the |
| preferred alignment to @option{-mpreferred-stack-boundary=2}. |
| |
| @item -mmmx |
| @itemx -mno-mmx |
| @itemx -msse |
| @itemx -mno-sse |
| @itemx -msse2 |
| @itemx -mno-sse2 |
| @itemx -msse3 |
| @itemx -mno-sse3 |
| @itemx -mssse3 |
| @itemx -mno-ssse3 |
| @itemx -msse4.1 |
| @need 800 |
| @itemx -mno-sse4.1 |
| @itemx -msse4.2 |
| @itemx -mno-sse4.2 |
| @itemx -msse4 |
| @itemx -mno-sse4 |
| @itemx -mavx |
| @itemx -mno-avx |
| @itemx -mavx2 |
| @itemx -mno-avx2 |
| @itemx -maes |
| @itemx -mno-aes |
| @itemx -mpclmul |
| @need 800 |
| @itemx -mno-pclmul |
| @itemx -mfsgsbase |
| @itemx -mno-fsgsbase |
| @itemx -mrdrnd |
| @itemx -mno-rdrnd |
| @itemx -mf16c |
| @itemx -mno-f16c |
| @itemx -mfma |
| @itemx -mno-fma |
| @itemx -msse4a |
| @itemx -mno-sse4a |
| @itemx -mfma4 |
| @need 800 |
| @itemx -mno-fma4 |
| @itemx -mxop |
| @itemx -mno-xop |
| @itemx -mlwp |
| @itemx -mno-lwp |
| @itemx -m3dnow |
| @itemx -mno-3dnow |
| @itemx -mpopcnt |
| @itemx -mno-popcnt |
| @itemx -mabm |
| @itemx -mno-abm |
| @itemx -mbmi |
| @itemx -mbmi2 |
| @itemx -mno-bmi |
| @itemx -mno-bmi2 |
| @itemx -mlzcnt |
| @itemx -mno-lzcnt |
| @itemx -mrtm |
| @itemx -mtbm |
| @itemx -mno-tbm |
| @opindex mmmx |
| @opindex mno-mmx |
| @opindex msse |
| @opindex mno-sse |
| @opindex m3dnow |
| @opindex mno-3dnow |
| These switches enable or disable the use of instructions in the MMX, SSE, |
| SSE2, SSE3, SSSE3, SSE4.1, AVX, AVX2, AES, PCLMUL, FSGSBASE, RDRND, F16C, |
| FMA, SSE4A, FMA4, XOP, LWP, ABM, BMI, BMI2, LZCNT, RTM or 3DNow!@: |
| extended instruction sets. |
| These extensions are also available as built-in functions: see |
| @ref{X86 Built-in Functions}, for details of the functions enabled and |
| disabled by these switches. |
| |
| To generate SSE/SSE2 instructions automatically from floating-point |
| code (as opposed to 387 instructions), see @option{-mfpmath=sse}. |
| |
| GCC depresses SSEx instructions when @option{-mavx} is used. Instead, it |
| generates new AVX instructions or AVX equivalence for all SSEx instructions |
| when needed. |
| |
| These options enable GCC to use these extended instructions in |
| generated code, even without @option{-mfpmath=sse}. Applications that |
| perform run-time CPU detection must compile separate files for each |
| supported architecture, using the appropriate flags. In particular, |
| the file containing the CPU detection code should be compiled without |
| these options. |
| |
| @item -mcld |
| @opindex mcld |
| This option instructs GCC to emit a @code{cld} instruction in the prologue |
| of functions that use string instructions. String instructions depend on |
| the DF flag to select between autoincrement or autodecrement mode. While the |
| ABI specifies the DF flag to be cleared on function entry, some operating |
| systems violate this specification by not clearing the DF flag in their |
| exception dispatchers. The exception handler can be invoked with the DF flag |
| set, which leads to wrong direction mode when string instructions are used. |
| This option can be enabled by default on 32-bit x86 targets by configuring |
| GCC with the @option{--enable-cld} configure option. Generation of @code{cld} |
| instructions can be suppressed with the @option{-mno-cld} compiler option |
| in this case. |
| |
| @item -mvzeroupper |
| @opindex mvzeroupper |
| This option instructs GCC to emit a @code{vzeroupper} instruction |
| before a transfer of control flow out of the function to minimize |
| the AVX to SSE transition penalty as well as remove unnecessary @code{zeroupper} |
| intrinsics. |
| |
| @item -mcx16 |
| @opindex mcx16 |
| This option enables GCC to generate @code{CMPXCHG16B} instructions. |
| @code{CMPXCHG16B} allows for atomic operations on 128-bit double quadword |
| (or oword) data types. |
| This is useful for high-resolution counters that can be updated |
| by multiple processors (or cores). This instruction is generated as part of |
| atomic built-in functions: see @ref{__sync Builtins} or |
| @ref{__atomic Builtins} for details. |
| |
| @item -msahf |
| @opindex msahf |
| This option enables generation of @code{SAHF} instructions in 64-bit code. |
| Early Intel Pentium 4 CPUs with Intel 64 support, |
| prior to the introduction of Pentium 4 G1 step in December 2005, |
| lacked the @code{LAHF} and @code{SAHF} instructions |
| which were supported by AMD64. |
| These are load and store instructions, respectively, for certain status flags. |
| In 64-bit mode, the @code{SAHF} instruction is used to optimize @code{fmod}, |
| @code{drem}, and @code{remainder} built-in functions; |
| see @ref{Other Builtins} for details. |
| |
| @item -mmovbe |
| @opindex mmovbe |
| This option enables use of the @code{movbe} instruction to implement |
| @code{__builtin_bswap32} and @code{__builtin_bswap64}. |
| |
| @item -mcrc32 |
| @opindex mcrc32 |
| This option enables built-in functions @code{__builtin_ia32_crc32qi}, |
| @code{__builtin_ia32_crc32hi}, @code{__builtin_ia32_crc32si} and |
| @code{__builtin_ia32_crc32di} to generate the @code{crc32} machine instruction. |
| |
| @item -mrecip |
| @opindex mrecip |
| This option enables use of @code{RCPSS} and @code{RSQRTSS} instructions |
| (and their vectorized variants @code{RCPPS} and @code{RSQRTPS}) |
| with an additional Newton-Raphson step |
| to increase precision instead of @code{DIVSS} and @code{SQRTSS} |
| (and their vectorized |
| variants) for single-precision floating-point arguments. These instructions |
| are generated only when @option{-funsafe-math-optimizations} is enabled |
| together with @option{-finite-math-only} and @option{-fno-trapping-math}. |
| Note that while the throughput of the sequence is higher than the throughput |
| of the non-reciprocal instruction, the precision of the sequence can be |
| decreased by up to 2 ulp (i.e. the inverse of 1.0 equals 0.99999994). |
| |
| Note that GCC implements @code{1.0f/sqrtf(@var{x})} in terms of @code{RSQRTSS} |
| (or @code{RSQRTPS}) already with @option{-ffast-math} (or the above option |
| combination), and doesn't need @option{-mrecip}. |
| |
| Also note that GCC emits the above sequence with additional Newton-Raphson step |
| for vectorized single-float division and vectorized @code{sqrtf(@var{x})} |
| already with @option{-ffast-math} (or the above option combination), and |
| doesn't need @option{-mrecip}. |
| |
| @item -mrecip=@var{opt} |
| @opindex mrecip=opt |
| This option controls which reciprocal estimate instructions |
| may be used. @var{opt} is a comma-separated list of options, which may |
| be preceded by a @samp{!} to invert the option: |
| |
| @table @samp |
| @item all |
| Enable all estimate instructions. |
| |
| @item default |
| Enable the default instructions, equivalent to @option{-mrecip}. |
| |
| @item none |
| Disable all estimate instructions, equivalent to @option{-mno-recip}. |
| |
| @item div |
| Enable the approximation for scalar division. |
| |
| @item vec-div |
| Enable the approximation for vectorized division. |
| |
| @item sqrt |
| Enable the approximation for scalar square root. |
| |
| @item vec-sqrt |
| Enable the approximation for vectorized square root. |
| @end table |
| |
| So, for example, @option{-mrecip=all,!sqrt} enables |
| all of the reciprocal approximations, except for square root. |
| |
| @item -mveclibabi=@var{type} |
| @opindex mveclibabi |
| Specifies the ABI type to use for vectorizing intrinsics using an |
| external library. Supported values for @var{type} are @samp{svml} |
| for the Intel short |
| vector math library and @samp{acml} for the AMD math core library. |
| To use this option, both @option{-ftree-vectorize} and |
| @option{-funsafe-math-optimizations} have to be enabled, and an SVML or ACML |
| ABI-compatible library must be specified at link time. |
| |
| GCC currently emits calls to @code{vmldExp2}, |
| @code{vmldLn2}, @code{vmldLog102}, @code{vmldLog102}, @code{vmldPow2}, |
| @code{vmldTanh2}, @code{vmldTan2}, @code{vmldAtan2}, @code{vmldAtanh2}, |
| @code{vmldCbrt2}, @code{vmldSinh2}, @code{vmldSin2}, @code{vmldAsinh2}, |
| @code{vmldAsin2}, @code{vmldCosh2}, @code{vmldCos2}, @code{vmldAcosh2}, |
| @code{vmldAcos2}, @code{vmlsExp4}, @code{vmlsLn4}, @code{vmlsLog104}, |
| @code{vmlsLog104}, @code{vmlsPow4}, @code{vmlsTanh4}, @code{vmlsTan4}, |
| @code{vmlsAtan4}, @code{vmlsAtanh4}, @code{vmlsCbrt4}, @code{vmlsSinh4}, |
| @code{vmlsSin4}, @code{vmlsAsinh4}, @code{vmlsAsin4}, @code{vmlsCosh4}, |
| @code{vmlsCos4}, @code{vmlsAcosh4} and @code{vmlsAcos4} for corresponding |
| function type when @option{-mveclibabi=svml} is used, and @code{__vrd2_sin}, |
| @code{__vrd2_cos}, @code{__vrd2_exp}, @code{__vrd2_log}, @code{__vrd2_log2}, |
| @code{__vrd2_log10}, @code{__vrs4_sinf}, @code{__vrs4_cosf}, |
| @code{__vrs4_expf}, @code{__vrs4_logf}, @code{__vrs4_log2f}, |
| @code{__vrs4_log10f} and @code{__vrs4_powf} for the corresponding function type |
| when @option{-mveclibabi=acml} is used. |
| |
| @item -mabi=@var{name} |
| @opindex mabi |
| Generate code for the specified calling convention. Permissible values |
| are @samp{sysv} for the ABI used on GNU/Linux and other systems, and |
| @samp{ms} for the Microsoft ABI. The default is to use the Microsoft |
| ABI when targeting Microsoft Windows and the SysV ABI on all other systems. |
| You can control this behavior for a specific function by |
| using the function attribute @samp{ms_abi}/@samp{sysv_abi}. |
| @xref{Function Attributes}. |
| |
| @item -mtls-dialect=@var{type} |
| @opindex mtls-dialect |
| Generate code to access thread-local storage using the @samp{gnu} or |
| @samp{gnu2} conventions. @samp{gnu} is the conservative default; |
| @samp{gnu2} is more efficient, but it may add compile- and run-time |
| requirements that cannot be satisfied on all systems. |
| |
| @item -mpush-args |
| @itemx -mno-push-args |
| @opindex mpush-args |
| @opindex mno-push-args |
| Use PUSH operations to store outgoing parameters. This method is shorter |
| and usually equally fast as method using SUB/MOV operations and is enabled |
| by default. In some cases disabling it may improve performance because of |
| improved scheduling and reduced dependencies. |
| |
| @item -maccumulate-outgoing-args |
| @opindex maccumulate-outgoing-args |
| If enabled, the maximum amount of space required for outgoing arguments is |
| computed in the function prologue. This is faster on most modern CPUs |
| because of reduced dependencies, improved scheduling and reduced stack usage |
| when the preferred stack boundary is not equal to 2. The drawback is a notable |
| increase in code size. This switch implies @option{-mno-push-args}. |
| |
| @item -mthreads |
| @opindex mthreads |
| Support thread-safe exception handling on MinGW. Programs that rely |
| on thread-safe exception handling must compile and link all code with the |
| @option{-mthreads} option. When compiling, @option{-mthreads} defines |
| @code{-D_MT}; when linking, it links in a special thread helper library |
| @option{-lmingwthrd} which cleans up per-thread exception-handling data. |
| |
| @item -mno-align-stringops |
| @opindex mno-align-stringops |
| Do not align the destination of inlined string operations. This switch reduces |
| code size and improves performance in case the destination is already aligned, |
| but GCC doesn't know about it. |
| |
| @item -minline-all-stringops |
| @opindex minline-all-stringops |
| By default GCC inlines string operations only when the destination is |
| known to be aligned to least a 4-byte boundary. |
| This enables more inlining and increases code |
| size, but may improve performance of code that depends on fast |
| @code{memcpy}, @code{strlen}, |
| and @code{memset} for short lengths. |
| |
| @item -minline-stringops-dynamically |
| @opindex minline-stringops-dynamically |
| For string operations of unknown size, use run-time checks with |
| inline code for small blocks and a library call for large blocks. |
| |
| @item -mstringop-strategy=@var{alg} |
| @opindex mstringop-strategy=@var{alg} |
| Override the internal decision heuristic for the particular algorithm to use |
| for inlining string operations. The allowed values for @var{alg} are: |
| |
| @table @samp |
| @item rep_byte |
| @itemx rep_4byte |
| @itemx rep_8byte |
| Expand using i386 @code{rep} prefix of the specified size. |
| |
| @item byte_loop |
| @itemx loop |
| @itemx unrolled_loop |
| Expand into an inline loop. |
| |
| @item libcall |
| Always use a library call. |
| @end table |
| |
| @item -momit-leaf-frame-pointer |
| @opindex momit-leaf-frame-pointer |
| Don't keep the frame pointer in a register for leaf functions. This |
| avoids the instructions to save, set up, and restore frame pointers and |
| makes an extra register available in leaf functions. The option |
| @option{-fomit-leaf-frame-pointer} removes the frame pointer for leaf functions, |
| which might make debugging harder. |
| |
| @item -mtls-direct-seg-refs |
| @itemx -mno-tls-direct-seg-refs |
| @opindex mtls-direct-seg-refs |
| Controls whether TLS variables may be accessed with offsets from the |
| TLS segment register (@code{%gs} for 32-bit, @code{%fs} for 64-bit), |
| or whether the thread base pointer must be added. Whether or not this |
| is valid depends on the operating system, and whether it maps the |
| segment to cover the entire TLS area. |
| |
| For systems that use the GNU C Library, the default is on. |
| |
| @item -msse2avx |
| @itemx -mno-sse2avx |
| @opindex msse2avx |
| Specify that the assembler should encode SSE instructions with VEX |
| prefix. The option @option{-mavx} turns this on by default. |
| |
| @item -mfentry |
| @itemx -mno-fentry |
| @opindex mfentry |
| If profiling is active (@option{-pg}), put the profiling |
| counter call before the prologue. |
| Note: On x86 architectures the attribute @code{ms_hook_prologue} |
| isn't possible at the moment for @option{-mfentry} and @option{-pg}. |
| |
| @item -m8bit-idiv |
| @itemx -mno-8bit-idiv |
| @opindex 8bit-idiv |
| On some processors, like Intel Atom, 8-bit unsigned integer divide is |
| much faster than 32-bit/64-bit integer divide. This option generates a |
| run-time check. If both dividend and divisor are within range of 0 |
| to 255, 8-bit unsigned integer divide is used instead of |
| 32-bit/64-bit integer divide. |
| |
| @item -mavx256-split-unaligned-load |
| @itemx -mavx256-split-unaligned-store |
| @opindex avx256-split-unaligned-load |
| @opindex avx256-split-unaligned-store |
| Split 32-byte AVX unaligned load and store. |
| |
| @end table |
| |
| These @samp{-m} switches are supported in addition to the above |
| on x86-64 processors in 64-bit environments. |
| |
| @table @gcctabopt |
| @item -m32 |
| @itemx -m64 |
| @itemx -mx32 |
| @opindex m32 |
| @opindex m64 |
| @opindex mx32 |
| Generate code for a 32-bit or 64-bit environment. |
| The @option{-m32} option sets @code{int}, @code{long}, and pointer types |
| to 32 bits, and |
| generates code that runs on any i386 system. |
| |
| The @option{-m64} option sets @code{int} to 32 bits and @code{long} and pointer |
| types to 64 bits, and generates code for the x86-64 architecture. |
| For Darwin only the @option{-m64} option also turns off the @option{-fno-pic} |
| and @option{-mdynamic-no-pic} options. |
| |
| The @option{-mx32} option sets @code{int}, @code{long}, and pointer types |
| to 32 bits, and |
| generates code for the x86-64 architecture. |
| |
| @item -mno-red-zone |
| @opindex mno-red-zone |
| Do not use a so-called ``red zone'' for x86-64 code. The red zone is mandated |
| by the x86-64 ABI; it is a 128-byte area beyond the location of the |
| stack pointer that is not modified by signal or interrupt handlers |
| and therefore can be used for temporary data without adjusting the stack |
| pointer. The flag @option{-mno-red-zone} disables this red zone. |
| |
| @item -mcmodel=small |
| @opindex mcmodel=small |
| Generate code for the small code model: the program and its symbols must |
| be linked in the lower 2 GB of the address space. Pointers are 64 bits. |
| Programs can be statically or dynamically linked. This is the default |
| code model. |
| |
| @item -mcmodel=kernel |
| @opindex mcmodel=kernel |
| Generate code for the kernel code model. The kernel runs in the |
| negative 2 GB of the address space. |
| This model has to be used for Linux kernel code. |
| |
| @item -mcmodel=medium |
| @opindex mcmodel=medium |
| Generate code for the medium model: the program is linked in the lower 2 |
| GB of the address space. Small symbols are also placed there. Symbols |
| with sizes larger than @option{-mlarge-data-threshold} are put into |
| large data or BSS sections and can be located above 2GB. Programs can |
| be statically or dynamically linked. |
| |
| @item -mcmodel=large |
| @opindex mcmodel=large |
| Generate code for the large model. This model makes no assumptions |
| about addresses and sizes of sections. |
| |
| @item -maddress-mode=long |
| @opindex maddress-mode=long |
| Generate code for long address mode. This is only supported for 64-bit |
| and x32 environments. It is the default address mode for 64-bit |
| environments. |
| |
| @item -maddress-mode=short |
| @opindex maddress-mode=short |
| Generate code for short address mode. This is only supported for 32-bit |
| and x32 environments. It is the default address mode for 32-bit and |
| x32 environments. |
| @end table |
| |
| @node i386 and x86-64 Windows Options |
| @subsection i386 and x86-64 Windows Options |
| @cindex i386 and x86-64 Windows Options |
| |
| These additional options are available for Microsoft Windows targets: |
| |
| @table @gcctabopt |
| @item -mconsole |
| @opindex mconsole |
| This option |
| specifies that a console application is to be generated, by |
| instructing the linker to set the PE header subsystem type |
| required for console applications. |
| This option is available for Cygwin and MinGW targets and is |
| enabled by default on those targets. |
| |
| @item -mdll |
| @opindex mdll |
| This option is available for Cygwin and MinGW targets. It |
| specifies that a DLL---a dynamic link library---is to be |
| generated, enabling the selection of the required runtime |
| startup object and entry point. |
| |
| @item -mnop-fun-dllimport |
| @opindex mnop-fun-dllimport |
| This option is available for Cygwin and MinGW targets. It |
| specifies that the @code{dllimport} attribute should be ignored. |
| |
| @item -mthread |
| @opindex mthread |
| This option is available for MinGW targets. It specifies |
| that MinGW-specific thread support is to be used. |
| |
| @item -municode |
| @opindex municode |
| This option is available for MinGW-w64 targets. It causes |
| the @code{UNICODE} preprocessor macro to be predefined, and |
| chooses Unicode-capable runtime startup code. |
| |
| @item -mwin32 |
| @opindex mwin32 |
| This option is available for Cygwin and MinGW targets. It |
| specifies that the typical Microsoft Windows predefined macros are to |
| be set in the pre-processor, but does not influence the choice |
| of runtime library/startup code. |
| |
| @item -mwindows |
| @opindex mwindows |
| This option is available for Cygwin and MinGW targets. It |
| specifies that a GUI application is to be generated by |
| instructing the linker to set the PE header subsystem type |
| appropriately. |
| |
| @item -fno-set-stack-executable |
| @opindex fno-set-stack-executable |
| This option is available for MinGW targets. It specifies that |
| the executable flag for the stack used by nested functions isn't |
| set. This is necessary for binaries running in kernel mode of |
| Microsoft Windows, as there the User32 API, which is used to set executable |
| privileges, isn't available. |
| |
| @item -fwritable-relocated-rdata |
| @opindex fno-writable-relocated-rdata |
| This option is available for MinGW and Cygwin targets. It specifies |
| that relocated-data in read-only section is put into .data |
| section. This is a necessary for older runtimes not supporting |
| modification of .rdata sections for pseudo-relocation. |
| |
| @item -mpe-aligned-commons |
| @opindex mpe-aligned-commons |
| This option is available for Cygwin and MinGW targets. It |
| specifies that the GNU extension to the PE file format that |
| permits the correct alignment of COMMON variables should be |
| used when generating code. It is enabled by default if |
| GCC detects that the target assembler found during configuration |
| supports the feature. |
| @end table |
| |
| See also under @ref{i386 and x86-64 Options} for standard options. |
| |
| @node IA-64 Options |
| @subsection IA-64 Options |
| @cindex IA-64 Options |
| |
| These are the @samp{-m} options defined for the Intel IA-64 architecture. |
| |
| @table @gcctabopt |
| @item -mbig-endian |
| @opindex mbig-endian |
| Generate code for a big-endian target. This is the default for HP-UX@. |
| |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate code for a little-endian target. This is the default for AIX5 |
| and GNU/Linux. |
| |
| @item -mgnu-as |
| @itemx -mno-gnu-as |
| @opindex mgnu-as |
| @opindex mno-gnu-as |
| Generate (or don't) code for the GNU assembler. This is the default. |
| @c Also, this is the default if the configure option @option{--with-gnu-as} |
| @c is used. |
| |
| @item -mgnu-ld |
| @itemx -mno-gnu-ld |
| @opindex mgnu-ld |
| @opindex mno-gnu-ld |
| Generate (or don't) code for the GNU linker. This is the default. |
| @c Also, this is the default if the configure option @option{--with-gnu-ld} |
| @c is used. |
| |
| @item -mno-pic |
| @opindex mno-pic |
| Generate code that does not use a global pointer register. The result |
| is not position independent code, and violates the IA-64 ABI@. |
| |
| @item -mvolatile-asm-stop |
| @itemx -mno-volatile-asm-stop |
| @opindex mvolatile-asm-stop |
| @opindex mno-volatile-asm-stop |
| Generate (or don't) a stop bit immediately before and after volatile asm |
| statements. |
| |
| @item -mregister-names |
| @itemx -mno-register-names |
| @opindex mregister-names |
| @opindex mno-register-names |
| Generate (or don't) @samp{in}, @samp{loc}, and @samp{out} register names for |
| the stacked registers. This may make assembler output more readable. |
| |
| @item -mno-sdata |
| @itemx -msdata |
| @opindex mno-sdata |
| @opindex msdata |
| Disable (or enable) optimizations that use the small data section. This may |
| be useful for working around optimizer bugs. |
| |
| @item -mconstant-gp |
| @opindex mconstant-gp |
| Generate code that uses a single constant global pointer value. This is |
| useful when compiling kernel code. |
| |
| @item -mauto-pic |
| @opindex mauto-pic |
| Generate code that is self-relocatable. This implies @option{-mconstant-gp}. |
| This is useful when compiling firmware code. |
| |
| @item -minline-float-divide-min-latency |
| @opindex minline-float-divide-min-latency |
| Generate code for inline divides of floating-point values |
| using the minimum latency algorithm. |
| |
| @item -minline-float-divide-max-throughput |
| @opindex minline-float-divide-max-throughput |
| Generate code for inline divides of floating-point values |
| using the maximum throughput algorithm. |
| |
| @item -mno-inline-float-divide |
| @opindex mno-inline-float-divide |
| Do not generate inline code for divides of floating-point values. |
| |
| @item -minline-int-divide-min-latency |
| @opindex minline-int-divide-min-latency |
| Generate code for inline divides of integer values |
| using the minimum latency algorithm. |
| |
| @item -minline-int-divide-max-throughput |
| @opindex minline-int-divide-max-throughput |
| Generate code for inline divides of integer values |
| using the maximum throughput algorithm. |
| |
| @item -mno-inline-int-divide |
| @opindex mno-inline-int-divide |
| Do not generate inline code for divides of integer values. |
| |
| @item -minline-sqrt-min-latency |
| @opindex minline-sqrt-min-latency |
| Generate code for inline square roots |
| using the minimum latency algorithm. |
| |
| @item -minline-sqrt-max-throughput |
| @opindex minline-sqrt-max-throughput |
| Generate code for inline square roots |
| using the maximum throughput algorithm. |
| |
| @item -mno-inline-sqrt |
| @opindex mno-inline-sqrt |
| Do not generate inline code for @code{sqrt}. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Do (don't) generate code that uses the fused multiply/add or multiply/subtract |
| instructions. The default is to use these instructions. |
| |
| @item -mno-dwarf2-asm |
| @itemx -mdwarf2-asm |
| @opindex mno-dwarf2-asm |
| @opindex mdwarf2-asm |
| Don't (or do) generate assembler code for the DWARF 2 line number debugging |
| info. This may be useful when not using the GNU assembler. |
| |
| @item -mearly-stop-bits |
| @itemx -mno-early-stop-bits |
| @opindex mearly-stop-bits |
| @opindex mno-early-stop-bits |
| Allow stop bits to be placed earlier than immediately preceding the |
| instruction that triggered the stop bit. This can improve instruction |
| scheduling, but does not always do so. |
| |
| @item -mfixed-range=@var{register-range} |
| @opindex mfixed-range |
| Generate code treating the given register range as fixed registers. |
| A fixed register is one that the register allocator cannot use. This is |
| useful when compiling kernel code. A register range is specified as |
| two registers separated by a dash. Multiple register ranges can be |
| specified separated by a comma. |
| |
| @item -mtls-size=@var{tls-size} |
| @opindex mtls-size |
| Specify bit size of immediate TLS offsets. Valid values are 14, 22, and |
| 64. |
| |
| @item -mtune=@var{cpu-type} |
| @opindex mtune |
| Tune the instruction scheduling for a particular CPU, Valid values are |
| @samp{itanium}, @samp{itanium1}, @samp{merced}, @samp{itanium2}, |
| and @samp{mckinley}. |
| |
| @item -milp32 |
| @itemx -mlp64 |
| @opindex milp32 |
| @opindex mlp64 |
| Generate code for a 32-bit or 64-bit environment. |
| The 32-bit environment sets int, long and pointer to 32 bits. |
| The 64-bit environment sets int to 32 bits and long and pointer |
| to 64 bits. These are HP-UX specific flags. |
| |
| @item -mno-sched-br-data-spec |
| @itemx -msched-br-data-spec |
| @opindex mno-sched-br-data-spec |
| @opindex msched-br-data-spec |
| (Dis/En)able data speculative scheduling before reload. |
| This results in generation of @code{ld.a} instructions and |
| the corresponding check instructions (@code{ld.c} / @code{chk.a}). |
| The default is 'disable'. |
| |
| @item -msched-ar-data-spec |
| @itemx -mno-sched-ar-data-spec |
| @opindex msched-ar-data-spec |
| @opindex mno-sched-ar-data-spec |
| (En/Dis)able data speculative scheduling after reload. |
| This results in generation of @code{ld.a} instructions and |
| the corresponding check instructions (@code{ld.c} / @code{chk.a}). |
| The default is 'enable'. |
| |
| @item -mno-sched-control-spec |
| @itemx -msched-control-spec |
| @opindex mno-sched-control-spec |
| @opindex msched-control-spec |
| (Dis/En)able control speculative scheduling. This feature is |
| available only during region scheduling (i.e.@: before reload). |
| This results in generation of the @code{ld.s} instructions and |
| the corresponding check instructions @code{chk.s}. |
| The default is 'disable'. |
| |
| @item -msched-br-in-data-spec |
| @itemx -mno-sched-br-in-data-spec |
| @opindex msched-br-in-data-spec |
| @opindex mno-sched-br-in-data-spec |
| (En/Dis)able speculative scheduling of the instructions that |
| are dependent on the data speculative loads before reload. |
| This is effective only with @option{-msched-br-data-spec} enabled. |
| The default is 'enable'. |
| |
| @item -msched-ar-in-data-spec |
| @itemx -mno-sched-ar-in-data-spec |
| @opindex msched-ar-in-data-spec |
| @opindex mno-sched-ar-in-data-spec |
| (En/Dis)able speculative scheduling of the instructions that |
| are dependent on the data speculative loads after reload. |
| This is effective only with @option{-msched-ar-data-spec} enabled. |
| The default is 'enable'. |
| |
| @item -msched-in-control-spec |
| @itemx -mno-sched-in-control-spec |
| @opindex msched-in-control-spec |
| @opindex mno-sched-in-control-spec |
| (En/Dis)able speculative scheduling of the instructions that |
| are dependent on the control speculative loads. |
| This is effective only with @option{-msched-control-spec} enabled. |
| The default is 'enable'. |
| |
| @item -mno-sched-prefer-non-data-spec-insns |
| @itemx -msched-prefer-non-data-spec-insns |
| @opindex mno-sched-prefer-non-data-spec-insns |
| @opindex msched-prefer-non-data-spec-insns |
| If enabled, data-speculative instructions are chosen for schedule |
| only if there are no other choices at the moment. This makes |
| the use of the data speculation much more conservative. |
| The default is 'disable'. |
| |
| @item -mno-sched-prefer-non-control-spec-insns |
| @itemx -msched-prefer-non-control-spec-insns |
| @opindex mno-sched-prefer-non-control-spec-insns |
| @opindex msched-prefer-non-control-spec-insns |
| If enabled, control-speculative instructions are chosen for schedule |
| only if there are no other choices at the moment. This makes |
| the use of the control speculation much more conservative. |
| The default is 'disable'. |
| |
| @item -mno-sched-count-spec-in-critical-path |
| @itemx -msched-count-spec-in-critical-path |
| @opindex mno-sched-count-spec-in-critical-path |
| @opindex msched-count-spec-in-critical-path |
| If enabled, speculative dependencies are considered during |
| computation of the instructions priorities. This makes the use of the |
| speculation a bit more conservative. |
| The default is 'disable'. |
| |
| @item -msched-spec-ldc |
| @opindex msched-spec-ldc |
| Use a simple data speculation check. This option is on by default. |
| |
| @item -msched-control-spec-ldc |
| @opindex msched-spec-ldc |
| Use a simple check for control speculation. This option is on by default. |
| |
| @item -msched-stop-bits-after-every-cycle |
| @opindex msched-stop-bits-after-every-cycle |
| Place a stop bit after every cycle when scheduling. This option is on |
| by default. |
| |
| @item -msched-fp-mem-deps-zero-cost |
| @opindex msched-fp-mem-deps-zero-cost |
| Assume that floating-point stores and loads are not likely to cause a conflict |
| when placed into the same instruction group. This option is disabled by |
| default. |
| |
| @item -msel-sched-dont-check-control-spec |
| @opindex msel-sched-dont-check-control-spec |
| Generate checks for control speculation in selective scheduling. |
| This flag is disabled by default. |
| |
| @item -msched-max-memory-insns=@var{max-insns} |
| @opindex msched-max-memory-insns |
| Limit on the number of memory insns per instruction group, giving lower |
| priority to subsequent memory insns attempting to schedule in the same |
| instruction group. Frequently useful to prevent cache bank conflicts. |
| The default value is 1. |
| |
| @item -msched-max-memory-insns-hard-limit |
| @opindex msched-max-memory-insns-hard-limit |
| Makes the limit specified by @option{msched-max-memory-insns} a hard limit, |
| disallowing more than that number in an instruction group. |
| Otherwise, the limit is ``soft'', meaning that non-memory operations |
| are preferred when the limit is reached, but memory operations may still |
| be scheduled. |
| |
| @end table |
| |
| @node LM32 Options |
| @subsection LM32 Options |
| @cindex LM32 options |
| |
| These @option{-m} options are defined for the LatticeMico32 architecture: |
| |
| @table @gcctabopt |
| @item -mbarrel-shift-enabled |
| @opindex mbarrel-shift-enabled |
| Enable barrel-shift instructions. |
| |
| @item -mdivide-enabled |
| @opindex mdivide-enabled |
| Enable divide and modulus instructions. |
| |
| @item -mmultiply-enabled |
| @opindex multiply-enabled |
| Enable multiply instructions. |
| |
| @item -msign-extend-enabled |
| @opindex msign-extend-enabled |
| Enable sign extend instructions. |
| |
| @item -muser-enabled |
| @opindex muser-enabled |
| Enable user-defined instructions. |
| |
| @end table |
| |
| @node M32C Options |
| @subsection M32C Options |
| @cindex M32C options |
| |
| @table @gcctabopt |
| @item -mcpu=@var{name} |
| @opindex mcpu= |
| Select the CPU for which code is generated. @var{name} may be one of |
| @samp{r8c} for the R8C/Tiny series, @samp{m16c} for the M16C (up to |
| /60) series, @samp{m32cm} for the M16C/80 series, or @samp{m32c} for |
| the M32C/80 series. |
| |
| @item -msim |
| @opindex msim |
| Specifies that the program will be run on the simulator. This causes |
| an alternate runtime library to be linked in which supports, for |
| example, file I/O@. You must not use this option when generating |
| programs that will run on real hardware; you must provide your own |
| runtime library for whatever I/O functions are needed. |
| |
| @item -memregs=@var{number} |
| @opindex memregs= |
| Specifies the number of memory-based pseudo-registers GCC uses |
| during code generation. These pseudo-registers are used like real |
| registers, so there is a tradeoff between GCC's ability to fit the |
| code into available registers, and the performance penalty of using |
| memory instead of registers. Note that all modules in a program must |
| be compiled with the same value for this option. Because of that, you |
| must not use this option with GCC's default runtime libraries. |
| |
| @end table |
| |
| @node M32R/D Options |
| @subsection M32R/D Options |
| @cindex M32R/D options |
| |
| These @option{-m} options are defined for Renesas M32R/D architectures: |
| |
| @table @gcctabopt |
| @item -m32r2 |
| @opindex m32r2 |
| Generate code for the M32R/2@. |
| |
| @item -m32rx |
| @opindex m32rx |
| Generate code for the M32R/X@. |
| |
| @item -m32r |
| @opindex m32r |
| Generate code for the M32R@. This is the default. |
| |
| @item -mmodel=small |
| @opindex mmodel=small |
| Assume all objects live in the lower 16MB of memory (so that their addresses |
| can be loaded with the @code{ld24} instruction), and assume all subroutines |
| are reachable with the @code{bl} instruction. |
| This is the default. |
| |
| The addressability of a particular object can be set with the |
| @code{model} attribute. |
| |
| @item -mmodel=medium |
| @opindex mmodel=medium |
| Assume objects may be anywhere in the 32-bit address space (the compiler |
| generates @code{seth/add3} instructions to load their addresses), and |
| assume all subroutines are reachable with the @code{bl} instruction. |
| |
| @item -mmodel=large |
| @opindex mmodel=large |
| Assume objects may be anywhere in the 32-bit address space (the compiler |
| generates @code{seth/add3} instructions to load their addresses), and |
| assume subroutines may not be reachable with the @code{bl} instruction |
| (the compiler generates the much slower @code{seth/add3/jl} |
| instruction sequence). |
| |
| @item -msdata=none |
| @opindex msdata=none |
| Disable use of the small data area. Variables are put into |
| one of @samp{.data}, @samp{.bss}, or @samp{.rodata} (unless the |
| @code{section} attribute has been specified). |
| This is the default. |
| |
| The small data area consists of sections @samp{.sdata} and @samp{.sbss}. |
| Objects may be explicitly put in the small data area with the |
| @code{section} attribute using one of these sections. |
| |
| @item -msdata=sdata |
| @opindex msdata=sdata |
| Put small global and static data in the small data area, but do not |
| generate special code to reference them. |
| |
| @item -msdata=use |
| @opindex msdata=use |
| Put small global and static data in the small data area, and generate |
| special instructions to reference them. |
| |
| @item -G @var{num} |
| @opindex G |
| @cindex smaller data references |
| Put global and static objects less than or equal to @var{num} bytes |
| into the small data or BSS sections instead of the normal data or BSS |
| sections. The default value of @var{num} is 8. |
| The @option{-msdata} option must be set to one of @samp{sdata} or @samp{use} |
| for this option to have any effect. |
| |
| All modules should be compiled with the same @option{-G @var{num}} value. |
| Compiling with different values of @var{num} may or may not work; if it |
| doesn't the linker gives an error message---incorrect code is not |
| generated. |
| |
| @item -mdebug |
| @opindex mdebug |
| Makes the M32R-specific code in the compiler display some statistics |
| that might help in debugging programs. |
| |
| @item -malign-loops |
| @opindex malign-loops |
| Align all loops to a 32-byte boundary. |
| |
| @item -mno-align-loops |
| @opindex mno-align-loops |
| Do not enforce a 32-byte alignment for loops. This is the default. |
| |
| @item -missue-rate=@var{number} |
| @opindex missue-rate=@var{number} |
| Issue @var{number} instructions per cycle. @var{number} can only be 1 |
| or 2. |
| |
| @item -mbranch-cost=@var{number} |
| @opindex mbranch-cost=@var{number} |
| @var{number} can only be 1 or 2. If it is 1 then branches are |
| preferred over conditional code, if it is 2, then the opposite applies. |
| |
| @item -mflush-trap=@var{number} |
| @opindex mflush-trap=@var{number} |
| Specifies the trap number to use to flush the cache. The default is |
| 12. Valid numbers are between 0 and 15 inclusive. |
| |
| @item -mno-flush-trap |
| @opindex mno-flush-trap |
| Specifies that the cache cannot be flushed by using a trap. |
| |
| @item -mflush-func=@var{name} |
| @opindex mflush-func=@var{name} |
| Specifies the name of the operating system function to call to flush |
| the cache. The default is @emph{_flush_cache}, but a function call |
| is only used if a trap is not available. |
| |
| @item -mno-flush-func |
| @opindex mno-flush-func |
| Indicates that there is no OS function for flushing the cache. |
| |
| @end table |
| |
| @node M680x0 Options |
| @subsection M680x0 Options |
| @cindex M680x0 options |
| |
| These are the @samp{-m} options defined for M680x0 and ColdFire processors. |
| The default settings depend on which architecture was selected when |
| the compiler was configured; the defaults for the most common choices |
| are given below. |
| |
| @table @gcctabopt |
| @item -march=@var{arch} |
| @opindex march |
| Generate code for a specific M680x0 or ColdFire instruction set |
| architecture. Permissible values of @var{arch} for M680x0 |
| architectures are: @samp{68000}, @samp{68010}, @samp{68020}, |
| @samp{68030}, @samp{68040}, @samp{68060} and @samp{cpu32}. ColdFire |
| architectures are selected according to Freescale's ISA classification |
| and the permissible values are: @samp{isaa}, @samp{isaaplus}, |
| @samp{isab} and @samp{isac}. |
| |
| GCC defines a macro @samp{__mcf@var{arch}__} whenever it is generating |
| code for a ColdFire target. The @var{arch} in this macro is one of the |
| @option{-march} arguments given above. |
| |
| When used together, @option{-march} and @option{-mtune} select code |
| that runs on a family of similar processors but that is optimized |
| for a particular microarchitecture. |
| |
| @item -mcpu=@var{cpu} |
| @opindex mcpu |
| Generate code for a specific M680x0 or ColdFire processor. |
| The M680x0 @var{cpu}s are: @samp{68000}, @samp{68010}, @samp{68020}, |
| @samp{68030}, @samp{68040}, @samp{68060}, @samp{68302}, @samp{68332} |
| and @samp{cpu32}. The ColdFire @var{cpu}s are given by the table |
| below, which also classifies the CPUs into families: |
| |
| @multitable @columnfractions 0.20 0.80 |
| @item @strong{Family} @tab @strong{@samp{-mcpu} arguments} |
| @item @samp{51} @tab @samp{51} @samp{51ac} @samp{51ag} @samp{51cn} @samp{51em} @samp{51je} @samp{51jf} @samp{51jg} @samp{51jm} @samp{51mm} @samp{51qe} @samp{51qm} |
| @item @samp{5206} @tab @samp{5202} @samp{5204} @samp{5206} |
| @item @samp{5206e} @tab @samp{5206e} |
| @item @samp{5208} @tab @samp{5207} @samp{5208} |
| @item @samp{5211a} @tab @samp{5210a} @samp{5211a} |
| @item @samp{5213} @tab @samp{5211} @samp{5212} @samp{5213} |
| @item @samp{5216} @tab @samp{5214} @samp{5216} |
| @item @samp{52235} @tab @samp{52230} @samp{52231} @samp{52232} @samp{52233} @samp{52234} @samp{52235} |
| @item @samp{5225} @tab @samp{5224} @samp{5225} |
| @item @samp{52259} @tab @samp{52252} @samp{52254} @samp{52255} @samp{52256} @samp{52258} @samp{52259} |
| @item @samp{5235} @tab @samp{5232} @samp{5233} @samp{5234} @samp{5235} @samp{523x} |
| @item @samp{5249} @tab @samp{5249} |
| @item @samp{5250} @tab @samp{5250} |
| @item @samp{5271} @tab @samp{5270} @samp{5271} |
| @item @samp{5272} @tab @samp{5272} |
| @item @samp{5275} @tab @samp{5274} @samp{5275} |
| @item @samp{5282} @tab @samp{5280} @samp{5281} @samp{5282} @samp{528x} |
| @item @samp{53017} @tab @samp{53011} @samp{53012} @samp{53013} @samp{53014} @samp{53015} @samp{53016} @samp{53017} |
| @item @samp{5307} @tab @samp{5307} |
| @item @samp{5329} @tab @samp{5327} @samp{5328} @samp{5329} @samp{532x} |
| @item @samp{5373} @tab @samp{5372} @samp{5373} @samp{537x} |
| @item @samp{5407} @tab @samp{5407} |
| @item @samp{5475} @tab @samp{5470} @samp{5471} @samp{5472} @samp{5473} @samp{5474} @samp{5475} @samp{547x} @samp{5480} @samp{5481} @samp{5482} @samp{5483} @samp{5484} @samp{5485} |
| @end multitable |
| |
| @option{-mcpu=@var{cpu}} overrides @option{-march=@var{arch}} if |
| @var{arch} is compatible with @var{cpu}. Other combinations of |
| @option{-mcpu} and @option{-march} are rejected. |
| |
| GCC defines the macro @samp{__mcf_cpu_@var{cpu}} when ColdFire target |
| @var{cpu} is selected. It also defines @samp{__mcf_family_@var{family}}, |
| where the value of @var{family} is given by the table above. |
| |
| @item -mtune=@var{tune} |
| @opindex mtune |
| Tune the code for a particular microarchitecture within the |
| constraints set by @option{-march} and @option{-mcpu}. |
| The M680x0 microarchitectures are: @samp{68000}, @samp{68010}, |
| @samp{68020}, @samp{68030}, @samp{68040}, @samp{68060} |
| and @samp{cpu32}. The ColdFire microarchitectures |
| are: @samp{cfv1}, @samp{cfv2}, @samp{cfv3}, @samp{cfv4} and @samp{cfv4e}. |
| |
| You can also use @option{-mtune=68020-40} for code that needs |
| to run relatively well on 68020, 68030 and 68040 targets. |
| @option{-mtune=68020-60} is similar but includes 68060 targets |
| as well. These two options select the same tuning decisions as |
| @option{-m68020-40} and @option{-m68020-60} respectively. |
| |
| GCC defines the macros @samp{__mc@var{arch}} and @samp{__mc@var{arch}__} |
| when tuning for 680x0 architecture @var{arch}. It also defines |
| @samp{mc@var{arch}} unless either @option{-ansi} or a non-GNU @option{-std} |
| option is used. If GCC is tuning for a range of architectures, |
| as selected by @option{-mtune=68020-40} or @option{-mtune=68020-60}, |
| it defines the macros for every architecture in the range. |
| |
| GCC also defines the macro @samp{__m@var{uarch}__} when tuning for |
| ColdFire microarchitecture @var{uarch}, where @var{uarch} is one |
| of the arguments given above. |
| |
| @item -m68000 |
| @itemx -mc68000 |
| @opindex m68000 |
| @opindex mc68000 |
| Generate output for a 68000. This is the default |
| when the compiler is configured for 68000-based systems. |
| It is equivalent to @option{-march=68000}. |
| |
| Use this option for microcontrollers with a 68000 or EC000 core, |
| including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356. |
| |
| @item -m68010 |
| @opindex m68010 |
| Generate output for a 68010. This is the default |
| when the compiler is configured for 68010-based systems. |
| It is equivalent to @option{-march=68010}. |
| |
| @item -m68020 |
| @itemx -mc68020 |
| @opindex m68020 |
| @opindex mc68020 |
| Generate output for a 68020. This is the default |
| when the compiler is configured for 68020-based systems. |
| It is equivalent to @option{-march=68020}. |
| |
| @item -m68030 |
| @opindex m68030 |
| Generate output for a 68030. This is the default when the compiler is |
| configured for 68030-based systems. It is equivalent to |
| @option{-march=68030}. |
| |
| @item -m68040 |
| @opindex m68040 |
| Generate output for a 68040. This is the default when the compiler is |
| configured for 68040-based systems. It is equivalent to |
| @option{-march=68040}. |
| |
| This option inhibits the use of 68881/68882 instructions that have to be |
| emulated by software on the 68040. Use this option if your 68040 does not |
| have code to emulate those instructions. |
| |
| @item -m68060 |
| @opindex m68060 |
| Generate output for a 68060. This is the default when the compiler is |
| configured for 68060-based systems. It is equivalent to |
| @option{-march=68060}. |
| |
| This option inhibits the use of 68020 and 68881/68882 instructions that |
| have to be emulated by software on the 68060. Use this option if your 68060 |
| does not have code to emulate those instructions. |
| |
| @item -mcpu32 |
| @opindex mcpu32 |
| Generate output for a CPU32. This is the default |
| when the compiler is configured for CPU32-based systems. |
| It is equivalent to @option{-march=cpu32}. |
| |
| Use this option for microcontrollers with a |
| CPU32 or CPU32+ core, including the 68330, 68331, 68332, 68333, 68334, |
| 68336, 68340, 68341, 68349 and 68360. |
| |
| @item -m5200 |
| @opindex m5200 |
| Generate output for a 520X ColdFire CPU@. This is the default |
| when the compiler is configured for 520X-based systems. |
| It is equivalent to @option{-mcpu=5206}, and is now deprecated |
| in favor of that option. |
| |
| Use this option for microcontroller with a 5200 core, including |
| the MCF5202, MCF5203, MCF5204 and MCF5206. |
| |
| @item -m5206e |
| @opindex m5206e |
| Generate output for a 5206e ColdFire CPU@. The option is now |
| deprecated in favor of the equivalent @option{-mcpu=5206e}. |
| |
| @item -m528x |
| @opindex m528x |
| Generate output for a member of the ColdFire 528X family. |
| The option is now deprecated in favor of the equivalent |
| @option{-mcpu=528x}. |
| |
| @item -m5307 |
| @opindex m5307 |
| Generate output for a ColdFire 5307 CPU@. The option is now deprecated |
| in favor of the equivalent @option{-mcpu=5307}. |
| |
| @item -m5407 |
| @opindex m5407 |
| Generate output for a ColdFire 5407 CPU@. The option is now deprecated |
| in favor of the equivalent @option{-mcpu=5407}. |
| |
| @item -mcfv4e |
| @opindex mcfv4e |
| Generate output for a ColdFire V4e family CPU (e.g.@: 547x/548x). |
| This includes use of hardware floating-point instructions. |
| The option is equivalent to @option{-mcpu=547x}, and is now |
| deprecated in favor of that option. |
| |
| @item -m68020-40 |
| @opindex m68020-40 |
| Generate output for a 68040, without using any of the new instructions. |
| This results in code that can run relatively efficiently on either a |
| 68020/68881 or a 68030 or a 68040. The generated code does use the |
| 68881 instructions that are emulated on the 68040. |
| |
| The option is equivalent to @option{-march=68020} @option{-mtune=68020-40}. |
| |
| @item -m68020-60 |
| @opindex m68020-60 |
| Generate output for a 68060, without using any of the new instructions. |
| This results in code that can run relatively efficiently on either a |
| 68020/68881 or a 68030 or a 68040. The generated code does use the |
| 68881 instructions that are emulated on the 68060. |
| |
| The option is equivalent to @option{-march=68020} @option{-mtune=68020-60}. |
| |
| @item -mhard-float |
| @itemx -m68881 |
| @opindex mhard-float |
| @opindex m68881 |
| Generate floating-point instructions. This is the default for 68020 |
| and above, and for ColdFire devices that have an FPU@. It defines the |
| macro @samp{__HAVE_68881__} on M680x0 targets and @samp{__mcffpu__} |
| on ColdFire targets. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Do not generate floating-point instructions; use library calls instead. |
| This is the default for 68000, 68010, and 68832 targets. It is also |
| the default for ColdFire devices that have no FPU. |
| |
| @item -mdiv |
| @itemx -mno-div |
| @opindex mdiv |
| @opindex mno-div |
| Generate (do not generate) ColdFire hardware divide and remainder |
| instructions. If @option{-march} is used without @option{-mcpu}, |
| the default is ``on'' for ColdFire architectures and ``off'' for M680x0 |
| architectures. Otherwise, the default is taken from the target CPU |
| (either the default CPU, or the one specified by @option{-mcpu}). For |
| example, the default is ``off'' for @option{-mcpu=5206} and ``on'' for |
| @option{-mcpu=5206e}. |
| |
| GCC defines the macro @samp{__mcfhwdiv__} when this option is enabled. |
| |
| @item -mshort |
| @opindex mshort |
| Consider type @code{int} to be 16 bits wide, like @code{short int}. |
| Additionally, parameters passed on the stack are also aligned to a |
| 16-bit boundary even on targets whose API mandates promotion to 32-bit. |
| |
| @item -mno-short |
| @opindex mno-short |
| Do not consider type @code{int} to be 16 bits wide. This is the default. |
| |
| @item -mnobitfield |
| @itemx -mno-bitfield |
| @opindex mnobitfield |
| @opindex mno-bitfield |
| Do not use the bit-field instructions. The @option{-m68000}, @option{-mcpu32} |
| and @option{-m5200} options imply @w{@option{-mnobitfield}}. |
| |
| @item -mbitfield |
| @opindex mbitfield |
| Do use the bit-field instructions. The @option{-m68020} option implies |
| @option{-mbitfield}. This is the default if you use a configuration |
| designed for a 68020. |
| |
| @item -mrtd |
| @opindex mrtd |
| Use a different function-calling convention, in which functions |
| that take a fixed number of arguments return with the @code{rtd} |
| instruction, which pops their arguments while returning. This |
| saves one instruction in the caller since there is no need to pop |
| the arguments there. |
| |
| This calling convention is incompatible with the one normally |
| used on Unix, so you cannot use it if you need to call libraries |
| compiled with the Unix compiler. |
| |
| Also, you must provide function prototypes for all functions that |
| take variable numbers of arguments (including @code{printf}); |
| otherwise incorrect code is generated for calls to those |
| functions. |
| |
| In addition, seriously incorrect code results if you call a |
| function with too many arguments. (Normally, extra arguments are |
| harmlessly ignored.) |
| |
| The @code{rtd} instruction is supported by the 68010, 68020, 68030, |
| 68040, 68060 and CPU32 processors, but not by the 68000 or 5200. |
| |
| @item -mno-rtd |
| @opindex mno-rtd |
| Do not use the calling conventions selected by @option{-mrtd}. |
| This is the default. |
| |
| @item -malign-int |
| @itemx -mno-align-int |
| @opindex malign-int |
| @opindex mno-align-int |
| Control whether GCC aligns @code{int}, @code{long}, @code{long long}, |
| @code{float}, @code{double}, and @code{long double} variables on a 32-bit |
| boundary (@option{-malign-int}) or a 16-bit boundary (@option{-mno-align-int}). |
| Aligning variables on 32-bit boundaries produces code that runs somewhat |
| faster on processors with 32-bit busses at the expense of more memory. |
| |
| @strong{Warning:} if you use the @option{-malign-int} switch, GCC |
| aligns structures containing the above types differently than |
| most published application binary interface specifications for the m68k. |
| |
| @item -mpcrel |
| @opindex mpcrel |
| Use the pc-relative addressing mode of the 68000 directly, instead of |
| using a global offset table. At present, this option implies @option{-fpic}, |
| allowing at most a 16-bit offset for pc-relative addressing. @option{-fPIC} is |
| not presently supported with @option{-mpcrel}, though this could be supported for |
| 68020 and higher processors. |
| |
| @item -mno-strict-align |
| @itemx -mstrict-align |
| @opindex mno-strict-align |
| @opindex mstrict-align |
| Do not (do) assume that unaligned memory references are handled by |
| the system. |
| |
| @item -msep-data |
| Generate code that allows the data segment to be located in a different |
| area of memory from the text segment. This allows for execute-in-place in |
| an environment without virtual memory management. This option implies |
| @option{-fPIC}. |
| |
| @item -mno-sep-data |
| Generate code that assumes that the data segment follows the text segment. |
| This is the default. |
| |
| @item -mid-shared-library |
| Generate code that supports shared libraries via the library ID method. |
| This allows for execute-in-place and shared libraries in an environment |
| without virtual memory management. This option implies @option{-fPIC}. |
| |
| @item -mno-id-shared-library |
| Generate code that doesn't assume ID-based shared libraries are being used. |
| This is the default. |
| |
| @item -mshared-library-id=n |
| Specifies the identification number of the ID-based shared library being |
| compiled. Specifying a value of 0 generates more compact code; specifying |
| other values forces the allocation of that number to the current |
| library, but is no more space- or time-efficient than omitting this option. |
| |
| @item -mxgot |
| @itemx -mno-xgot |
| @opindex mxgot |
| @opindex mno-xgot |
| When generating position-independent code for ColdFire, generate code |
| that works if the GOT has more than 8192 entries. This code is |
| larger and slower than code generated without this option. On M680x0 |
| processors, this option is not needed; @option{-fPIC} suffices. |
| |
| GCC normally uses a single instruction to load values from the GOT@. |
| While this is relatively efficient, it only works if the GOT |
| is smaller than about 64k. Anything larger causes the linker |
| to report an error such as: |
| |
| @cindex relocation truncated to fit (ColdFire) |
| @smallexample |
| relocation truncated to fit: R_68K_GOT16O foobar |
| @end smallexample |
| |
| If this happens, you should recompile your code with @option{-mxgot}. |
| It should then work with very large GOTs. However, code generated with |
| @option{-mxgot} is less efficient, since it takes 4 instructions to fetch |
| the value of a global symbol. |
| |
| Note that some linkers, including newer versions of the GNU linker, |
| can create multiple GOTs and sort GOT entries. If you have such a linker, |
| you should only need to use @option{-mxgot} when compiling a single |
| object file that accesses more than 8192 GOT entries. Very few do. |
| |
| These options have no effect unless GCC is generating |
| position-independent code. |
| |
| @end table |
| |
| @node MCore Options |
| @subsection MCore Options |
| @cindex MCore options |
| |
| These are the @samp{-m} options defined for the Motorola M*Core |
| processors. |
| |
| @table @gcctabopt |
| |
| @item -mhardlit |
| @itemx -mno-hardlit |
| @opindex mhardlit |
| @opindex mno-hardlit |
| Inline constants into the code stream if it can be done in two |
| instructions or less. |
| |
| @item -mdiv |
| @itemx -mno-div |
| @opindex mdiv |
| @opindex mno-div |
| Use the divide instruction. (Enabled by default). |
| |
| @item -mrelax-immediate |
| @itemx -mno-relax-immediate |
| @opindex mrelax-immediate |
| @opindex mno-relax-immediate |
| Allow arbitrary-sized immediates in bit operations. |
| |
| @item -mwide-bitfields |
| @itemx -mno-wide-bitfields |
| @opindex mwide-bitfields |
| @opindex mno-wide-bitfields |
| Always treat bit-fields as @code{int}-sized. |
| |
| @item -m4byte-functions |
| @itemx -mno-4byte-functions |
| @opindex m4byte-functions |
| @opindex mno-4byte-functions |
| Force all functions to be aligned to a 4-byte boundary. |
| |
| @item -mcallgraph-data |
| @itemx -mno-callgraph-data |
| @opindex mcallgraph-data |
| @opindex mno-callgraph-data |
| Emit callgraph information. |
| |
| @item -mslow-bytes |
| @itemx -mno-slow-bytes |
| @opindex mslow-bytes |
| @opindex mno-slow-bytes |
| Prefer word access when reading byte quantities. |
| |
| @item -mlittle-endian |
| @itemx -mbig-endian |
| @opindex mlittle-endian |
| @opindex mbig-endian |
| Generate code for a little-endian target. |
| |
| @item -m210 |
| @itemx -m340 |
| @opindex m210 |
| @opindex m340 |
| Generate code for the 210 processor. |
| |
| @item -mno-lsim |
| @opindex mno-lsim |
| Assume that runtime support has been provided and so omit the |
| simulator library (@file{libsim.a)} from the linker command line. |
| |
| @item -mstack-increment=@var{size} |
| @opindex mstack-increment |
| Set the maximum amount for a single stack increment operation. Large |
| values can increase the speed of programs that contain functions |
| that need a large amount of stack space, but they can also trigger a |
| segmentation fault if the stack is extended too much. The default |
| value is 0x1000. |
| |
| @end table |
| |
| @node MeP Options |
| @subsection MeP Options |
| @cindex MeP options |
| |
| @table @gcctabopt |
| |
| @item -mabsdiff |
| @opindex mabsdiff |
| Enables the @code{abs} instruction, which is the absolute difference |
| between two registers. |
| |
| @item -mall-opts |
| @opindex mall-opts |
| Enables all the optional instructions---average, multiply, divide, bit |
| operations, leading zero, absolute difference, min/max, clip, and |
| saturation. |
| |
| |
| @item -maverage |
| @opindex maverage |
| Enables the @code{ave} instruction, which computes the average of two |
| registers. |
| |
| @item -mbased=@var{n} |
| @opindex mbased= |
| Variables of size @var{n} bytes or smaller are placed in the |
| @code{.based} section by default. Based variables use the @code{$tp} |
| register as a base register, and there is a 128-byte limit to the |
| @code{.based} section. |
| |
| @item -mbitops |
| @opindex mbitops |
| Enables the bit operation instructions---bit test (@code{btstm}), set |
| (@code{bsetm}), clear (@code{bclrm}), invert (@code{bnotm}), and |
| test-and-set (@code{tas}). |
| |
| @item -mc=@var{name} |
| @opindex mc= |
| Selects which section constant data is placed in. @var{name} may |
| be @code{tiny}, @code{near}, or @code{far}. |
| |
| @item -mclip |
| @opindex mclip |
| Enables the @code{clip} instruction. Note that @code{-mclip} is not |
| useful unless you also provide @code{-mminmax}. |
| |
| @item -mconfig=@var{name} |
| @opindex mconfig= |
| Selects one of the built-in core configurations. Each MeP chip has |
| one or more modules in it; each module has a core CPU and a variety of |
| coprocessors, optional instructions, and peripherals. The |
| @code{MeP-Integrator} tool, not part of GCC, provides these |
| configurations through this option; using this option is the same as |
| using all the corresponding command-line options. The default |
| configuration is @code{default}. |
| |
| @item -mcop |
| @opindex mcop |
| Enables the coprocessor instructions. By default, this is a 32-bit |
| coprocessor. Note that the coprocessor is normally enabled via the |
| @code{-mconfig=} option. |
| |
| @item -mcop32 |
| @opindex mcop32 |
| Enables the 32-bit coprocessor's instructions. |
| |
| @item -mcop64 |
| @opindex mcop64 |
| Enables the 64-bit coprocessor's instructions. |
| |
| @item -mivc2 |
| @opindex mivc2 |
| Enables IVC2 scheduling. IVC2 is a 64-bit VLIW coprocessor. |
| |
| @item -mdc |
| @opindex mdc |
| Causes constant variables to be placed in the @code{.near} section. |
| |
| @item -mdiv |
| @opindex mdiv |
| Enables the @code{div} and @code{divu} instructions. |
| |
| @item -meb |
| @opindex meb |
| Generate big-endian code. |
| |
| @item -mel |
| @opindex mel |
| Generate little-endian code. |
| |
| @item -mio-volatile |
| @opindex mio-volatile |
| Tells the compiler that any variable marked with the @code{io} |
| attribute is to be considered volatile. |
| |
| @item -ml |
| @opindex ml |
| Causes variables to be assigned to the @code{.far} section by default. |
| |
| @item -mleadz |
| @opindex mleadz |
| Enables the @code{leadz} (leading zero) instruction. |
| |
| @item -mm |
| @opindex mm |
| Causes variables to be assigned to the @code{.near} section by default. |
| |
| @item -mminmax |
| @opindex mminmax |
| Enables the @code{min} and @code{max} instructions. |
| |
| @item -mmult |
| @opindex mmult |
| Enables the multiplication and multiply-accumulate instructions. |
| |
| @item -mno-opts |
| @opindex mno-opts |
| Disables all the optional instructions enabled by @code{-mall-opts}. |
| |
| @item -mrepeat |
| @opindex mrepeat |
| Enables the @code{repeat} and @code{erepeat} instructions, used for |
| low-overhead looping. |
| |
| @item -ms |
| @opindex ms |
| Causes all variables to default to the @code{.tiny} section. Note |
| that there is a 65536-byte limit to this section. Accesses to these |
| variables use the @code{%gp} base register. |
| |
| @item -msatur |
| @opindex msatur |
| Enables the saturation instructions. Note that the compiler does not |
| currently generate these itself, but this option is included for |
| compatibility with other tools, like @code{as}. |
| |
| @item -msdram |
| @opindex msdram |
| Link the SDRAM-based runtime instead of the default ROM-based runtime. |
| |
| @item -msim |
| @opindex msim |
| Link the simulator runtime libraries. |
| |
| @item -msimnovec |
| @opindex msimnovec |
| Link the simulator runtime libraries, excluding built-in support |
| for reset and exception vectors and tables. |
| |
| @item -mtf |
| @opindex mtf |
| Causes all functions to default to the @code{.far} section. Without |
| this option, functions default to the @code{.near} section. |
| |
| @item -mtiny=@var{n} |
| @opindex mtiny= |
| Variables that are @var{n} bytes or smaller are allocated to the |
| @code{.tiny} section. These variables use the @code{$gp} base |
| register. The default for this option is 4, but note that there's a |
| 65536-byte limit to the @code{.tiny} section. |
| |
| @end table |
| |
| @node MicroBlaze Options |
| @subsection MicroBlaze Options |
| @cindex MicroBlaze Options |
| |
| @table @gcctabopt |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Use software emulation for floating point (default). |
| |
| @item -mhard-float |
| @opindex mhard-float |
| Use hardware floating-point instructions. |
| |
| @item -mmemcpy |
| @opindex mmemcpy |
| Do not optimize block moves, use @code{memcpy}. |
| |
| @item -mno-clearbss |
| @opindex mno-clearbss |
| This option is deprecated. Use @option{-fno-zero-initialized-in-bss} instead. |
| |
| @item -mcpu=@var{cpu-type} |
| @opindex mcpu= |
| Use features of, and schedule code for, the given CPU. |
| Supported values are in the format @samp{v@var{X}.@var{YY}.@var{Z}}, |
| where @var{X} is a major version, @var{YY} is the minor version, and |
| @var{Z} is compatibility code. Example values are @samp{v3.00.a}, |
| @samp{v4.00.b}, @samp{v5.00.a}, @samp{v5.00.b}, @samp{v5.00.b}, @samp{v6.00.a}. |
| |
| @item -mxl-soft-mul |
| @opindex mxl-soft-mul |
| Use software multiply emulation (default). |
| |
| @item -mxl-soft-div |
| @opindex mxl-soft-div |
| Use software emulation for divides (default). |
| |
| @item -mxl-barrel-shift |
| @opindex mxl-barrel-shift |
| Use the hardware barrel shifter. |
| |
| @item -mxl-pattern-compare |
| @opindex mxl-pattern-compare |
| Use pattern compare instructions. |
| |
| @item -msmall-divides |
| @opindex msmall-divides |
| Use table lookup optimization for small signed integer divisions. |
| |
| @item -mxl-stack-check |
| @opindex mxl-stack-check |
| This option is deprecated. Use @option{-fstack-check} instead. |
| |
| @item -mxl-gp-opt |
| @opindex mxl-gp-opt |
| Use GP-relative @code{.sdata}/@code{.sbss} sections. |
| |
| @item -mxl-multiply-high |
| @opindex mxl-multiply-high |
| Use multiply high instructions for high part of 32x32 multiply. |
| |
| @item -mxl-float-convert |
| @opindex mxl-float-convert |
| Use hardware floating-point conversion instructions. |
| |
| @item -mxl-float-sqrt |
| @opindex mxl-float-sqrt |
| Use hardware floating-point square root instruction. |
| |
| @item -mxl-mode-@var{app-model} |
| Select application model @var{app-model}. Valid models are |
| @table @samp |
| @item executable |
| normal executable (default), uses startup code @file{crt0.o}. |
| |
| @item xmdstub |
| for use with Xilinx Microprocessor Debugger (XMD) based |
| software intrusive debug agent called xmdstub. This uses startup file |
| @file{crt1.o} and sets the start address of the program to 0x800. |
| |
| @item bootstrap |
| for applications that are loaded using a bootloader. |
| This model uses startup file @file{crt2.o} which does not contain a processor |
| reset vector handler. This is suitable for transferring control on a |
| processor reset to the bootloader rather than the application. |
| |
| @item novectors |
| for applications that do not require any of the |
| MicroBlaze vectors. This option may be useful for applications running |
| within a monitoring application. This model uses @file{crt3.o} as a startup file. |
| @end table |
| |
| Option @option{-xl-mode-@var{app-model}} is a deprecated alias for |
| @option{-mxl-mode-@var{app-model}}. |
| |
| @end table |
| |
| @node MIPS Options |
| @subsection MIPS Options |
| @cindex MIPS options |
| |
| @table @gcctabopt |
| |
| @item -EB |
| @opindex EB |
| Generate big-endian code. |
| |
| @item -EL |
| @opindex EL |
| Generate little-endian code. This is the default for @samp{mips*el-*-*} |
| configurations. |
| |
| @item -march=@var{arch} |
| @opindex march |
| Generate code that runs on @var{arch}, which can be the name of a |
| generic MIPS ISA, or the name of a particular processor. |
| The ISA names are: |
| @samp{mips1}, @samp{mips2}, @samp{mips3}, @samp{mips4}, |
| @samp{mips32}, @samp{mips32r2}, @samp{mips64} and @samp{mips64r2}. |
| The processor names are: |
| @samp{4kc}, @samp{4km}, @samp{4kp}, @samp{4ksc}, |
| @samp{4kec}, @samp{4kem}, @samp{4kep}, @samp{4ksd}, |
| @samp{5kc}, @samp{5kf}, |
| @samp{20kc}, |
| @samp{24kc}, @samp{24kf2_1}, @samp{24kf1_1}, |
| @samp{24kec}, @samp{24kef2_1}, @samp{24kef1_1}, |
| @samp{34kc}, @samp{34kf2_1}, @samp{34kf1_1}, @samp{34kn}, |
| @samp{74kc}, @samp{74kf2_1}, @samp{74kf1_1}, @samp{74kf3_2}, |
| @samp{1004kc}, @samp{1004kf2_1}, @samp{1004kf1_1}, |
| @samp{loongson2e}, @samp{loongson2f}, @samp{loongson3a}, |
| @samp{m4k}, |
| @samp{octeon}, @samp{octeon+}, @samp{octeon2}, |
| @samp{orion}, |
| @samp{r2000}, @samp{r3000}, @samp{r3900}, @samp{r4000}, @samp{r4400}, |
| @samp{r4600}, @samp{r4650}, @samp{r6000}, @samp{r8000}, |
| @samp{rm7000}, @samp{rm9000}, |
| @samp{r10000}, @samp{r12000}, @samp{r14000}, @samp{r16000}, |
| @samp{sb1}, |
| @samp{sr71000}, |
| @samp{vr4100}, @samp{vr4111}, @samp{vr4120}, @samp{vr4130}, @samp{vr4300}, |
| @samp{vr5000}, @samp{vr5400}, @samp{vr5500}, |
| @samp{xlr} and @samp{xlp}. |
| The special value @samp{from-abi} selects the |
| most compatible architecture for the selected ABI (that is, |
| @samp{mips1} for 32-bit ABIs and @samp{mips3} for 64-bit ABIs)@. |
| |
| The native Linux/GNU toolchain also supports the value @samp{native}, |
| which selects the best architecture option for the host processor. |
| @option{-march=native} has no effect if GCC does not recognize |
| the processor. |
| |
| In processor names, a final @samp{000} can be abbreviated as @samp{k} |
| (for example, @option{-march=r2k}). Prefixes are optional, and |
| @samp{vr} may be written @samp{r}. |
| |
| Names of the form @samp{@var{n}f2_1} refer to processors with |
| FPUs clocked at half the rate of the core, names of the form |
| @samp{@var{n}f1_1} refer to processors with FPUs clocked at the same |
| rate as the core, and names of the form @samp{@var{n}f3_2} refer to |
| processors with FPUs clocked a ratio of 3:2 with respect to the core. |
| For compatibility reasons, @samp{@var{n}f} is accepted as a synonym |
| for @samp{@var{n}f2_1} while @samp{@var{n}x} and @samp{@var{b}fx} are |
| accepted as synonyms for @samp{@var{n}f1_1}. |
| |
| GCC defines two macros based on the value of this option. The first |
| is @samp{_MIPS_ARCH}, which gives the name of target architecture, as |
| a string. The second has the form @samp{_MIPS_ARCH_@var{foo}}, |
| where @var{foo} is the capitalized value of @samp{_MIPS_ARCH}@. |
| For example, @option{-march=r2000} sets @samp{_MIPS_ARCH} |
| to @samp{"r2000"} and defines the macro @samp{_MIPS_ARCH_R2000}. |
| |
| Note that the @samp{_MIPS_ARCH} macro uses the processor names given |
| above. In other words, it has the full prefix and does not |
| abbreviate @samp{000} as @samp{k}. In the case of @samp{from-abi}, |
| the macro names the resolved architecture (either @samp{"mips1"} or |
| @samp{"mips3"}). It names the default architecture when no |
| @option{-march} option is given. |
| |
| @item -mtune=@var{arch} |
| @opindex mtune |
| Optimize for @var{arch}. Among other things, this option controls |
| the way instructions are scheduled, and the perceived cost of arithmetic |
| operations. The list of @var{arch} values is the same as for |
| @option{-march}. |
| |
| When this option is not used, GCC optimizes for the processor |
| specified by @option{-march}. By using @option{-march} and |
| @option{-mtune} together, it is possible to generate code that |
| runs on a family of processors, but optimize the code for one |
| particular member of that family. |
| |
| @option{-mtune} defines the macros @samp{_MIPS_TUNE} and |
| @samp{_MIPS_TUNE_@var{foo}}, which work in the same way as the |
| @option{-march} ones described above. |
| |
| @item -mips1 |
| @opindex mips1 |
| Equivalent to @option{-march=mips1}. |
| |
| @item -mips2 |
| @opindex mips2 |
| Equivalent to @option{-march=mips2}. |
| |
| @item -mips3 |
| @opindex mips3 |
| Equivalent to @option{-march=mips3}. |
| |
| @item -mips4 |
| @opindex mips4 |
| Equivalent to @option{-march=mips4}. |
| |
| @item -mips32 |
| @opindex mips32 |
| Equivalent to @option{-march=mips32}. |
| |
| @item -mips32r2 |
| @opindex mips32r2 |
| Equivalent to @option{-march=mips32r2}. |
| |
| @item -mips64 |
| @opindex mips64 |
| Equivalent to @option{-march=mips64}. |
| |
| @item -mips64r2 |
| @opindex mips64r2 |
| Equivalent to @option{-march=mips64r2}. |
| |
| @item -mips16 |
| @itemx -mno-mips16 |
| @opindex mips16 |
| @opindex mno-mips16 |
| Generate (do not generate) MIPS16 code. If GCC is targeting a |
| MIPS32 or MIPS64 architecture, it makes use of the MIPS16e ASE@. |
| |
| MIPS16 code generation can also be controlled on a per-function basis |
| by means of @code{mips16} and @code{nomips16} attributes. |
| @xref{Function Attributes}, for more information. |
| |
| @item -mflip-mips16 |
| @opindex mflip-mips16 |
| Generate MIPS16 code on alternating functions. This option is provided |
| for regression testing of mixed MIPS16/non-MIPS16 code generation, and is |
| not intended for ordinary use in compiling user code. |
| |
| @item -minterlink-mips16 |
| @itemx -mno-interlink-mips16 |
| @opindex minterlink-mips16 |
| @opindex mno-interlink-mips16 |
| Require (do not require) that non-MIPS16 code be link-compatible with |
| MIPS16 code. |
| |
| For example, non-MIPS16 code cannot jump directly to MIPS16 code; |
| it must either use a call or an indirect jump. @option{-minterlink-mips16} |
| therefore disables direct jumps unless GCC knows that the target of the |
| jump is not MIPS16. |
| |
| @item -mabi=32 |
| @itemx -mabi=o64 |
| @itemx -mabi=n32 |
| @itemx -mabi=64 |
| @itemx -mabi=eabi |
| @opindex mabi=32 |
| @opindex mabi=o64 |
| @opindex mabi=n32 |
| @opindex mabi=64 |
| @opindex mabi=eabi |
| Generate code for the given ABI@. |
| |
| Note that the EABI has a 32-bit and a 64-bit variant. GCC normally |
| generates 64-bit code when you select a 64-bit architecture, but you |
| can use @option{-mgp32} to get 32-bit code instead. |
| |
| For information about the O64 ABI, see |
| @uref{http://gcc.gnu.org/@/projects/@/mipso64-abi.html}. |
| |
| GCC supports a variant of the o32 ABI in which floating-point registers |
| are 64 rather than 32 bits wide. You can select this combination with |
| @option{-mabi=32} @option{-mfp64}. This ABI relies on the @code{mthc1} |
| and @code{mfhc1} instructions and is therefore only supported for |
| MIPS32R2 processors. |
| |
| The register assignments for arguments and return values remain the |
| same, but each scalar value is passed in a single 64-bit register |
| rather than a pair of 32-bit registers. For example, scalar |
| floating-point values are returned in @samp{$f0} only, not a |
| @samp{$f0}/@samp{$f1} pair. The set of call-saved registers also |
| remains the same, but all 64 bits are saved. |
| |
| @item -mabicalls |
| @itemx -mno-abicalls |
| @opindex mabicalls |
| @opindex mno-abicalls |
| Generate (do not generate) code that is suitable for SVR4-style |
| dynamic objects. @option{-mabicalls} is the default for SVR4-based |
| systems. |
| |
| @item -mshared |
| @itemx -mno-shared |
| Generate (do not generate) code that is fully position-independent, |
| and that can therefore be linked into shared libraries. This option |
| only affects @option{-mabicalls}. |
| |
| All @option{-mabicalls} code has traditionally been position-independent, |
| regardless of options like @option{-fPIC} and @option{-fpic}. However, |
| as an extension, the GNU toolchain allows executables to use absolute |
| accesses for locally-binding symbols. It can also use shorter GP |
| initialization sequences and generate direct calls to locally-defined |
| functions. This mode is selected by @option{-mno-shared}. |
| |
| @option{-mno-shared} depends on binutils 2.16 or higher and generates |
| objects that can only be linked by the GNU linker. However, the option |
| does not affect the ABI of the final executable; it only affects the ABI |
| of relocatable objects. Using @option{-mno-shared} generally makes |
| executables both smaller and quicker. |
| |
| @option{-mshared} is the default. |
| |
| @item -mplt |
| @itemx -mno-plt |
| @opindex mplt |
| @opindex mno-plt |
| Assume (do not assume) that the static and dynamic linkers |
| support PLTs and copy relocations. This option only affects |
| @option{-mno-shared -mabicalls}. For the n64 ABI, this option |
| has no effect without @option{-msym32}. |
| |
| You can make @option{-mplt} the default by configuring |
| GCC with @option{--with-mips-plt}. The default is |
| @option{-mno-plt} otherwise. |
| |
| @item -mxgot |
| @itemx -mno-xgot |
| @opindex mxgot |
| @opindex mno-xgot |
| Lift (do not lift) the usual restrictions on the size of the global |
| offset table. |
| |
| GCC normally uses a single instruction to load values from the GOT@. |
| While this is relatively efficient, it only works if the GOT |
| is smaller than about 64k. Anything larger causes the linker |
| to report an error such as: |
| |
| @cindex relocation truncated to fit (MIPS) |
| @smallexample |
| relocation truncated to fit: R_MIPS_GOT16 foobar |
| @end smallexample |
| |
| If this happens, you should recompile your code with @option{-mxgot}. |
| This works with very large GOTs, although the code is also |
| less efficient, since it takes three instructions to fetch the |
| value of a global symbol. |
| |
| Note that some linkers can create multiple GOTs. If you have such a |
| linker, you should only need to use @option{-mxgot} when a single object |
| file accesses more than 64k's worth of GOT entries. Very few do. |
| |
| These options have no effect unless GCC is generating position |
| independent code. |
| |
| @item -mgp32 |
| @opindex mgp32 |
| Assume that general-purpose registers are 32 bits wide. |
| |
| @item -mgp64 |
| @opindex mgp64 |
| Assume that general-purpose registers are 64 bits wide. |
| |
| @item -mfp32 |
| @opindex mfp32 |
| Assume that floating-point registers are 32 bits wide. |
| |
| @item -mfp64 |
| @opindex mfp64 |
| Assume that floating-point registers are 64 bits wide. |
| |
| @item -mhard-float |
| @opindex mhard-float |
| Use floating-point coprocessor instructions. |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Do not use floating-point coprocessor instructions. Implement |
| floating-point calculations using library calls instead. |
| |
| @item -mno-float |
| @opindex mno-float |
| Equivalent to @option{-msoft-float}, but additionally asserts that the |
| program being compiled does not perform any floating-point operations. |
| This option is presently supported only by some bare-metal MIPS |
| configurations, where it may select a special set of libraries |
| that lack all floating-point support (including, for example, the |
| floating-point @code{printf} formats). |
| If code compiled with @code{-mno-float} accidentally contains |
| floating-point operations, it is likely to suffer a link-time |
| or run-time failure. |
| |
| @item -msingle-float |
| @opindex msingle-float |
| Assume that the floating-point coprocessor only supports single-precision |
| operations. |
| |
| @item -mdouble-float |
| @opindex mdouble-float |
| Assume that the floating-point coprocessor supports double-precision |
| operations. This is the default. |
| |
| @item -mllsc |
| @itemx -mno-llsc |
| @opindex mllsc |
| @opindex mno-llsc |
| Use (do not use) @samp{ll}, @samp{sc}, and @samp{sync} instructions to |
| implement atomic memory built-in functions. When neither option is |
| specified, GCC uses the instructions if the target architecture |
| supports them. |
| |
| @option{-mllsc} is useful if the runtime environment can emulate the |
| instructions and @option{-mno-llsc} can be useful when compiling for |
| nonstandard ISAs. You can make either option the default by |
| configuring GCC with @option{--with-llsc} and @option{--without-llsc} |
| respectively. @option{--with-llsc} is the default for some |
| configurations; see the installation documentation for details. |
| |
| @item -mdsp |
| @itemx -mno-dsp |
| @opindex mdsp |
| @opindex mno-dsp |
| Use (do not use) revision 1 of the MIPS DSP ASE@. |
| @xref{MIPS DSP Built-in Functions}. This option defines the |
| preprocessor macro @samp{__mips_dsp}. It also defines |
| @samp{__mips_dsp_rev} to 1. |
| |
| @item -mdspr2 |
| @itemx -mno-dspr2 |
| @opindex mdspr2 |
| @opindex mno-dspr2 |
| Use (do not use) revision 2 of the MIPS DSP ASE@. |
| @xref{MIPS DSP Built-in Functions}. This option defines the |
| preprocessor macros @samp{__mips_dsp} and @samp{__mips_dspr2}. |
| It also defines @samp{__mips_dsp_rev} to 2. |
| |
| @item -msmartmips |
| @itemx -mno-smartmips |
| @opindex msmartmips |
| @opindex mno-smartmips |
| Use (do not use) the MIPS SmartMIPS ASE. |
| |
| @item -mpaired-single |
| @itemx -mno-paired-single |
| @opindex mpaired-single |
| @opindex mno-paired-single |
| Use (do not use) paired-single floating-point instructions. |
| @xref{MIPS Paired-Single Support}. This option requires |
| hardware floating-point support to be enabled. |
| |
| @item -mdmx |
| @itemx -mno-mdmx |
| @opindex mdmx |
| @opindex mno-mdmx |
| Use (do not use) MIPS Digital Media Extension instructions. |
| This option can only be used when generating 64-bit code and requires |
| hardware floating-point support to be enabled. |
| |
| @item -mips3d |
| @itemx -mno-mips3d |
| @opindex mips3d |
| @opindex mno-mips3d |
| Use (do not use) the MIPS-3D ASE@. @xref{MIPS-3D Built-in Functions}. |
| The option @option{-mips3d} implies @option{-mpaired-single}. |
| |
| @item -mmt |
| @itemx -mno-mt |
| @opindex mmt |
| @opindex mno-mt |
| Use (do not use) MT Multithreading instructions. |
| |
| @item -mmcu |
| @itemx -mno-mcu |
| @opindex mmcu |
| @opindex mno-mcu |
| Use (do not use) the MIPS MCU ASE instructions. |
| |
| @item -mlong64 |
| @opindex mlong64 |
| Force @code{long} types to be 64 bits wide. See @option{-mlong32} for |
| an explanation of the default and the way that the pointer size is |
| determined. |
| |
| @item -mlong32 |
| @opindex mlong32 |
| Force @code{long}, @code{int}, and pointer types to be 32 bits wide. |
| |
| The default size of @code{int}s, @code{long}s and pointers depends on |
| the ABI@. All the supported ABIs use 32-bit @code{int}s. The n64 ABI |
| uses 64-bit @code{long}s, as does the 64-bit EABI; the others use |
| 32-bit @code{long}s. Pointers are the same size as @code{long}s, |
| or the same size as integer registers, whichever is smaller. |
| |
| @item -msym32 |
| @itemx -mno-sym32 |
| @opindex msym32 |
| @opindex mno-sym32 |
| Assume (do not assume) that all symbols have 32-bit values, regardless |
| of the selected ABI@. This option is useful in combination with |
| @option{-mabi=64} and @option{-mno-abicalls} because it allows GCC |
| to generate shorter and faster references to symbolic addresses. |
| |
| @item -G @var{num} |
| @opindex G |
| Put definitions of externally-visible data in a small data section |
| if that data is no bigger than @var{num} bytes. GCC can then generate |
| more efficient accesses to the data; see @option{-mgpopt} for details. |
| |
| The default @option{-G} option depends on the configuration. |
| |
| @item -mlocal-sdata |
| @itemx -mno-local-sdata |
| @opindex mlocal-sdata |
| @opindex mno-local-sdata |
| Extend (do not extend) the @option{-G} behavior to local data too, |
| such as to static variables in C@. @option{-mlocal-sdata} is the |
| default for all configurations. |
| |
| If the linker complains that an application is using too much small data, |
| you might want to try rebuilding the less performance-critical parts with |
| @option{-mno-local-sdata}. You might also want to build large |
| libraries with @option{-mno-local-sdata}, so that the libraries leave |
| more room for the main program. |
| |
| @item -mextern-sdata |
| @itemx -mno-extern-sdata |
| @opindex mextern-sdata |
| @opindex mno-extern-sdata |
| Assume (do not assume) that externally-defined data is in |
| a small data section if the size of that data is within the @option{-G} limit. |
| @option{-mextern-sdata} is the default for all configurations. |
| |
| If you compile a module @var{Mod} with @option{-mextern-sdata} @option{-G |
| @var{num}} @option{-mgpopt}, and @var{Mod} references a variable @var{Var} |
| that is no bigger than @var{num} bytes, you must make sure that @var{Var} |
| is placed in a small data section. If @var{Var} is defined by another |
| module, you must either compile that module with a high-enough |
| @option{-G} setting or attach a @code{section} attribute to @var{Var}'s |
| definition. If @var{Var} is common, you must link the application |
| with a high-enough @option{-G} setting. |
| |
| The easiest way of satisfying these restrictions is to compile |
| and link every module with the same @option{-G} option. However, |
| you may wish to build a library that supports several different |
| small data limits. You can do this by compiling the library with |
| the highest supported @option{-G} setting and additionally using |
| @option{-mno-extern-sdata} to stop the library from making assumptions |
| about externally-defined data. |
| |
| @item -mgpopt |
| @itemx -mno-gpopt |
| @opindex mgpopt |
| @opindex mno-gpopt |
| Use (do not use) GP-relative accesses for symbols that are known to be |
| in a small data section; see @option{-G}, @option{-mlocal-sdata} and |
| @option{-mextern-sdata}. @option{-mgpopt} is the default for all |
| configurations. |
| |
| @option{-mno-gpopt} is useful for cases where the @code{$gp} register |
| might not hold the value of @code{_gp}. For example, if the code is |
| part of a library that might be used in a boot monitor, programs that |
| call boot monitor routines pass an unknown value in @code{$gp}. |
| (In such situations, the boot monitor itself is usually compiled |
| with @option{-G0}.) |
| |
| @option{-mno-gpopt} implies @option{-mno-local-sdata} and |
| @option{-mno-extern-sdata}. |
| |
| @item -membedded-data |
| @itemx -mno-embedded-data |
| @opindex membedded-data |
| @opindex mno-embedded-data |
| Allocate variables to the read-only data section first if possible, then |
| next in the small data section if possible, otherwise in data. This gives |
| slightly slower code than the default, but reduces the amount of RAM required |
| when executing, and thus may be preferred for some embedded systems. |
| |
| @item -muninit-const-in-rodata |
| @itemx -mno-uninit-const-in-rodata |
| @opindex muninit-const-in-rodata |
| @opindex mno-uninit-const-in-rodata |
| Put uninitialized @code{const} variables in the read-only data section. |
| This option is only meaningful in conjunction with @option{-membedded-data}. |
| |
| @item -mcode-readable=@var{setting} |
| @opindex mcode-readable |
| Specify whether GCC may generate code that reads from executable sections. |
| There are three possible settings: |
| |
| @table @gcctabopt |
| @item -mcode-readable=yes |
| Instructions may freely access executable sections. This is the |
| default setting. |
| |
| @item -mcode-readable=pcrel |
| MIPS16 PC-relative load instructions can access executable sections, |
| but other instructions must not do so. This option is useful on 4KSc |
| and 4KSd processors when the code TLBs have the Read Inhibit bit set. |
| It is also useful on processors that can be configured to have a dual |
| instruction/data SRAM interface and that, like the M4K, automatically |
| redirect PC-relative loads to the instruction RAM. |
| |
| @item -mcode-readable=no |
| Instructions must not access executable sections. This option can be |
| useful on targets that are configured to have a dual instruction/data |
| SRAM interface but that (unlike the M4K) do not automatically redirect |
| PC-relative loads to the instruction RAM. |
| @end table |
| |
| @item -msplit-addresses |
| @itemx -mno-split-addresses |
| @opindex msplit-addresses |
| @opindex mno-split-addresses |
| Enable (disable) use of the @code{%hi()} and @code{%lo()} assembler |
| relocation operators. This option has been superseded by |
| @option{-mexplicit-relocs} but is retained for backwards compatibility. |
| |
| @item -mexplicit-relocs |
| @itemx -mno-explicit-relocs |
| @opindex mexplicit-relocs |
| @opindex mno-explicit-relocs |
| Use (do not use) assembler relocation operators when dealing with symbolic |
| addresses. The alternative, selected by @option{-mno-explicit-relocs}, |
| is to use assembler macros instead. |
| |
| @option{-mexplicit-relocs} is the default if GCC was configured |
| to use an assembler that supports relocation operators. |
| |
| @item -mcheck-zero-division |
| @itemx -mno-check-zero-division |
| @opindex mcheck-zero-division |
| @opindex mno-check-zero-division |
| Trap (do not trap) on integer division by zero. |
| |
| The default is @option{-mcheck-zero-division}. |
| |
| @item -mdivide-traps |
| @itemx -mdivide-breaks |
| @opindex mdivide-traps |
| @opindex mdivide-breaks |
| MIPS systems check for division by zero by generating either a |
| conditional trap or a break instruction. Using traps results in |
| smaller code, but is only supported on MIPS II and later. Also, some |
| versions of the Linux kernel have a bug that prevents trap from |
| generating the proper signal (@code{SIGFPE}). Use @option{-mdivide-traps} to |
| allow conditional traps on architectures that support them and |
| @option{-mdivide-breaks} to force the use of breaks. |
| |
| The default is usually @option{-mdivide-traps}, but this can be |
| overridden at configure time using @option{--with-divide=breaks}. |
| Divide-by-zero checks can be completely disabled using |
| @option{-mno-check-zero-division}. |
| |
| @item -mmemcpy |
| @itemx -mno-memcpy |
| @opindex mmemcpy |
| @opindex mno-memcpy |
| Force (do not force) the use of @code{memcpy()} for non-trivial block |
| moves. The default is @option{-mno-memcpy}, which allows GCC to inline |
| most constant-sized copies. |
| |
| @item -mlong-calls |
| @itemx -mno-long-calls |
| @opindex mlong-calls |
| @opindex mno-long-calls |
| Disable (do not disable) use of the @code{jal} instruction. Calling |
| functions using @code{jal} is more efficient but requires the caller |
| and callee to be in the same 256 megabyte segment. |
| |
| This option has no effect on abicalls code. The default is |
| @option{-mno-long-calls}. |
| |
| @item -mmad |
| @itemx -mno-mad |
| @opindex mmad |
| @opindex mno-mad |
| Enable (disable) use of the @code{mad}, @code{madu} and @code{mul} |
| instructions, as provided by the R4650 ISA@. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Enable (disable) use of the floating-point multiply-accumulate |
| instructions, when they are available. The default is |
| @option{-mfused-madd}. |
| |
| When multiply-accumulate instructions are used, the intermediate |
| product is calculated to infinite precision and is not subject to |
| the FCSR Flush to Zero bit. This may be undesirable in some |
| circumstances. |
| |
| @item -nocpp |
| @opindex nocpp |
| Tell the MIPS assembler to not run its preprocessor over user |
| assembler files (with a @samp{.s} suffix) when assembling them. |
| |
| @item -mfix-24k |
| @item -mno-fix-24k |
| @opindex mfix-24k |
| @opindex mno-fix-24k |
| Work around the 24K E48 (lost data on stores during refill) errata. |
| The workarounds are implemented by the assembler rather than by GCC@. |
| |
| @item -mfix-r4000 |
| @itemx -mno-fix-r4000 |
| @opindex mfix-r4000 |
| @opindex mno-fix-r4000 |
| Work around certain R4000 CPU errata: |
| @itemize @minus |
| @item |
| A double-word or a variable shift may give an incorrect result if executed |
| immediately after starting an integer division. |
| @item |
| A double-word or a variable shift may give an incorrect result if executed |
| while an integer multiplication is in progress. |
| @item |
| An integer division may give an incorrect result if started in a delay slot |
| of a taken branch or a jump. |
| @end itemize |
| |
| @item -mfix-r4400 |
| @itemx -mno-fix-r4400 |
| @opindex mfix-r4400 |
| @opindex mno-fix-r4400 |
| Work around certain R4400 CPU errata: |
| @itemize @minus |
| @item |
| A double-word or a variable shift may give an incorrect result if executed |
| immediately after starting an integer division. |
| @end itemize |
| |
| @item -mfix-r10000 |
| @itemx -mno-fix-r10000 |
| @opindex mfix-r10000 |
| @opindex mno-fix-r10000 |
| Work around certain R10000 errata: |
| @itemize @minus |
| @item |
| @code{ll}/@code{sc} sequences may not behave atomically on revisions |
| prior to 3.0. They may deadlock on revisions 2.6 and earlier. |
| @end itemize |
| |
| This option can only be used if the target architecture supports |
| branch-likely instructions. @option{-mfix-r10000} is the default when |
| @option{-march=r10000} is used; @option{-mno-fix-r10000} is the default |
| otherwise. |
| |
| @item -mfix-vr4120 |
| @itemx -mno-fix-vr4120 |
| @opindex mfix-vr4120 |
| Work around certain VR4120 errata: |
| @itemize @minus |
| @item |
| @code{dmultu} does not always produce the correct result. |
| @item |
| @code{div} and @code{ddiv} do not always produce the correct result if one |
| of the operands is negative. |
| @end itemize |
| The workarounds for the division errata rely on special functions in |
| @file{libgcc.a}. At present, these functions are only provided by |
| the @code{mips64vr*-elf} configurations. |
| |
| Other VR4120 errata require a NOP to be inserted between certain pairs of |
| instructions. These errata are handled by the assembler, not by GCC itself. |
| |
| @item -mfix-vr4130 |
| @opindex mfix-vr4130 |
| Work around the VR4130 @code{mflo}/@code{mfhi} errata. The |
| workarounds are implemented by the assembler rather than by GCC, |
| although GCC avoids using @code{mflo} and @code{mfhi} if the |
| VR4130 @code{macc}, @code{macchi}, @code{dmacc} and @code{dmacchi} |
| instructions are available instead. |
| |
| @item -mfix-sb1 |
| @itemx -mno-fix-sb1 |
| @opindex mfix-sb1 |
| Work around certain SB-1 CPU core errata. |
| (This flag currently works around the SB-1 revision 2 |
| ``F1'' and ``F2'' floating-point errata.) |
| |
| @item -mr10k-cache-barrier=@var{setting} |
| @opindex mr10k-cache-barrier |
| Specify whether GCC should insert cache barriers to avoid the |
| side-effects of speculation on R10K processors. |
| |
| In common with many processors, the R10K tries to predict the outcome |
| of a conditional branch and speculatively executes instructions from |
| the ``taken'' branch. It later aborts these instructions if the |
| predicted outcome is wrong. However, on the R10K, even aborted |
| instructions can have side effects. |
| |
| This problem only affects kernel stores and, depending on the system, |
| kernel loads. As an example, a speculatively-executed store may load |
| the target memory into cache and mark the cache line as dirty, even if |
| the store itself is later aborted. If a DMA operation writes to the |
| same area of memory before the ``dirty'' line is flushed, the cached |
| data overwrites the DMA-ed data. See the R10K processor manual |
| for a full description, including other potential problems. |
| |
| One workaround is to insert cache barrier instructions before every memory |
| access that might be speculatively executed and that might have side |
| effects even if aborted. @option{-mr10k-cache-barrier=@var{setting}} |
| controls GCC's implementation of this workaround. It assumes that |
| aborted accesses to any byte in the following regions does not have |
| side effects: |
| |
| @enumerate |
| @item |
| the memory occupied by the current function's stack frame; |
| |
| @item |
| the memory occupied by an incoming stack argument; |
| |
| @item |
| the memory occupied by an object with a link-time-constant address. |
| @end enumerate |
| |
| It is the kernel's responsibility to ensure that speculative |
| accesses to these regions are indeed safe. |
| |
| If the input program contains a function declaration such as: |
| |
| @smallexample |
| void foo (void); |
| @end smallexample |
| |
| then the implementation of @code{foo} must allow @code{j foo} and |
| @code{jal foo} to be executed speculatively. GCC honors this |
| restriction for functions it compiles itself. It expects non-GCC |
| functions (such as hand-written assembly code) to do the same. |
| |
| The option has three forms: |
| |
| @table @gcctabopt |
| @item -mr10k-cache-barrier=load-store |
| Insert a cache barrier before a load or store that might be |
| speculatively executed and that might have side effects even |
| if aborted. |
| |
| @item -mr10k-cache-barrier=store |
| Insert a cache barrier before a store that might be speculatively |
| executed and that might have side effects even if aborted. |
| |
| @item -mr10k-cache-barrier=none |
| Disable the insertion of cache barriers. This is the default setting. |
| @end table |
| |
| @item -mflush-func=@var{func} |
| @itemx -mno-flush-func |
| @opindex mflush-func |
| Specifies the function to call to flush the I and D caches, or to not |
| call any such function. If called, the function must take the same |
| arguments as the common @code{_flush_func()}, that is, the address of the |
| memory range for which the cache is being flushed, the size of the |
| memory range, and the number 3 (to flush both caches). The default |
| depends on the target GCC was configured for, but commonly is either |
| @samp{_flush_func} or @samp{__cpu_flush}. |
| |
| @item mbranch-cost=@var{num} |
| @opindex mbranch-cost |
| Set the cost of branches to roughly @var{num} ``simple'' instructions. |
| This cost is only a heuristic and is not guaranteed to produce |
| consistent results across releases. A zero cost redundantly selects |
| the default, which is based on the @option{-mtune} setting. |
| |
| @item -mbranch-likely |
| @itemx -mno-branch-likely |
| @opindex mbranch-likely |
| @opindex mno-branch-likely |
| Enable or disable use of Branch Likely instructions, regardless of the |
| default for the selected architecture. By default, Branch Likely |
| instructions may be generated if they are supported by the selected |
| architecture. An exception is for the MIPS32 and MIPS64 architectures |
| and processors that implement those architectures; for those, Branch |
| Likely instructions are not be generated by default because the MIPS32 |
| and MIPS64 architectures specifically deprecate their use. |
| |
| @item -mfp-exceptions |
| @itemx -mno-fp-exceptions |
| @opindex mfp-exceptions |
| Specifies whether FP exceptions are enabled. This affects how |
| FP instructions are scheduled for some processors. |
| The default is that FP exceptions are |
| enabled. |
| |
| For instance, on the SB-1, if FP exceptions are disabled, and we are emitting |
| 64-bit code, then we can use both FP pipes. Otherwise, we can only use one |
| FP pipe. |
| |
| @item -mvr4130-align |
| @itemx -mno-vr4130-align |
| @opindex mvr4130-align |
| The VR4130 pipeline is two-way superscalar, but can only issue two |
| instructions together if the first one is 8-byte aligned. When this |
| option is enabled, GCC aligns pairs of instructions that it |
| thinks should execute in parallel. |
| |
| This option only has an effect when optimizing for the VR4130. |
| It normally makes code faster, but at the expense of making it bigger. |
| It is enabled by default at optimization level @option{-O3}. |
| |
| @item -msynci |
| @itemx -mno-synci |
| @opindex msynci |
| Enable (disable) generation of @code{synci} instructions on |
| architectures that support it. The @code{synci} instructions (if |
| enabled) are generated when @code{__builtin___clear_cache()} is |
| compiled. |
| |
| This option defaults to @code{-mno-synci}, but the default can be |
| overridden by configuring with @code{--with-synci}. |
| |
| When compiling code for single processor systems, it is generally safe |
| to use @code{synci}. However, on many multi-core (SMP) systems, it |
| does not invalidate the instruction caches on all cores and may lead |
| to undefined behavior. |
| |
| @item -mrelax-pic-calls |
| @itemx -mno-relax-pic-calls |
| @opindex mrelax-pic-calls |
| Try to turn PIC calls that are normally dispatched via register |
| @code{$25} into direct calls. This is only possible if the linker can |
| resolve the destination at link-time and if the destination is within |
| range for a direct call. |
| |
| @option{-mrelax-pic-calls} is the default if GCC was configured to use |
| an assembler and a linker that support the @code{.reloc} assembly |
| directive and @code{-mexplicit-relocs} is in effect. With |
| @code{-mno-explicit-relocs}, this optimization can be performed by the |
| assembler and the linker alone without help from the compiler. |
| |
| @item -mmcount-ra-address |
| @itemx -mno-mcount-ra-address |
| @opindex mmcount-ra-address |
| @opindex mno-mcount-ra-address |
| Emit (do not emit) code that allows @code{_mcount} to modify the |
| calling function's return address. When enabled, this option extends |
| the usual @code{_mcount} interface with a new @var{ra-address} |
| parameter, which has type @code{intptr_t *} and is passed in register |
| @code{$12}. @code{_mcount} can then modify the return address by |
| doing both of the following: |
| @itemize |
| @item |
| Returning the new address in register @code{$31}. |
| @item |
| Storing the new address in @code{*@var{ra-address}}, |
| if @var{ra-address} is nonnull. |
| @end itemize |
| |
| The default is @option{-mno-mcount-ra-address}. |
| |
| @end table |
| |
| @node MMIX Options |
| @subsection MMIX Options |
| @cindex MMIX Options |
| |
| These options are defined for the MMIX: |
| |
| @table @gcctabopt |
| @item -mlibfuncs |
| @itemx -mno-libfuncs |
| @opindex mlibfuncs |
| @opindex mno-libfuncs |
| Specify that intrinsic library functions are being compiled, passing all |
| values in registers, no matter the size. |
| |
| @item -mepsilon |
| @itemx -mno-epsilon |
| @opindex mepsilon |
| @opindex mno-epsilon |
| Generate floating-point comparison instructions that compare with respect |
| to the @code{rE} epsilon register. |
| |
| @item -mabi=mmixware |
| @itemx -mabi=gnu |
| @opindex mabi=mmixware |
| @opindex mabi=gnu |
| Generate code that passes function parameters and return values that (in |
| the called function) are seen as registers @code{$0} and up, as opposed to |
| the GNU ABI which uses global registers @code{$231} and up. |
| |
| @item -mzero-extend |
| @itemx -mno-zero-extend |
| @opindex mzero-extend |
| @opindex mno-zero-extend |
| When reading data from memory in sizes shorter than 64 bits, use (do not |
| use) zero-extending load instructions by default, rather than |
| sign-extending ones. |
| |
| @item -mknuthdiv |
| @itemx -mno-knuthdiv |
| @opindex mknuthdiv |
| @opindex mno-knuthdiv |
| Make the result of a division yielding a remainder have the same sign as |
| the divisor. With the default, @option{-mno-knuthdiv}, the sign of the |
| remainder follows the sign of the dividend. Both methods are |
| arithmetically valid, the latter being almost exclusively used. |
| |
| @item -mtoplevel-symbols |
| @itemx -mno-toplevel-symbols |
| @opindex mtoplevel-symbols |
| @opindex mno-toplevel-symbols |
| Prepend (do not prepend) a @samp{:} to all global symbols, so the assembly |
| code can be used with the @code{PREFIX} assembly directive. |
| |
| @item -melf |
| @opindex melf |
| Generate an executable in the ELF format, rather than the default |
| @samp{mmo} format used by the @command{mmix} simulator. |
| |
| @item -mbranch-predict |
| @itemx -mno-branch-predict |
| @opindex mbranch-predict |
| @opindex mno-branch-predict |
| Use (do not use) the probable-branch instructions, when static branch |
| prediction indicates a probable branch. |
| |
| @item -mbase-addresses |
| @itemx -mno-base-addresses |
| @opindex mbase-addresses |
| @opindex mno-base-addresses |
| Generate (do not generate) code that uses @emph{base addresses}. Using a |
| base address automatically generates a request (handled by the assembler |
| and the linker) for a constant to be set up in a global register. The |
| register is used for one or more base address requests within the range 0 |
| to 255 from the value held in the register. The generally leads to short |
| and fast code, but the number of different data items that can be |
| addressed is limited. This means that a program that uses lots of static |
| data may require @option{-mno-base-addresses}. |
| |
| @item -msingle-exit |
| @itemx -mno-single-exit |
| @opindex msingle-exit |
| @opindex mno-single-exit |
| Force (do not force) generated code to have a single exit point in each |
| function. |
| @end table |
| |
| @node MN10300 Options |
| @subsection MN10300 Options |
| @cindex MN10300 options |
| |
| These @option{-m} options are defined for Matsushita MN10300 architectures: |
| |
| @table @gcctabopt |
| @item -mmult-bug |
| @opindex mmult-bug |
| Generate code to avoid bugs in the multiply instructions for the MN10300 |
| processors. This is the default. |
| |
| @item -mno-mult-bug |
| @opindex mno-mult-bug |
| Do not generate code to avoid bugs in the multiply instructions for the |
| MN10300 processors. |
| |
| @item -mam33 |
| @opindex mam33 |
| Generate code using features specific to the AM33 processor. |
| |
| @item -mno-am33 |
| @opindex mno-am33 |
| Do not generate code using features specific to the AM33 processor. This |
| is the default. |
| |
| @item -mam33-2 |
| @opindex mam33-2 |
| Generate code using features specific to the AM33/2.0 processor. |
| |
| @item -mam34 |
| @opindex mam34 |
| Generate code using features specific to the AM34 processor. |
| |
| @item -mtune=@var{cpu-type} |
| @opindex mtune |
| Use the timing characteristics of the indicated CPU type when |
| scheduling instructions. This does not change the targeted processor |
| type. The CPU type must be one of @samp{mn10300}, @samp{am33}, |
| @samp{am33-2} or @samp{am34}. |
| |
| @item -mreturn-pointer-on-d0 |
| @opindex mreturn-pointer-on-d0 |
| When generating a function that returns a pointer, return the pointer |
| in both @code{a0} and @code{d0}. Otherwise, the pointer is returned |
| only in @code{a0}, and attempts to call such functions without a prototype |
| result in errors. Note that this option is on by default; use |
| @option{-mno-return-pointer-on-d0} to disable it. |
| |
| @item -mno-crt0 |
| @opindex mno-crt0 |
| Do not link in the C run-time initialization object file. |
| |
| @item -mrelax |
| @opindex mrelax |
| Indicate to the linker that it should perform a relaxation optimization pass |
| to shorten branches, calls and absolute memory addresses. This option only |
| has an effect when used on the command line for the final link step. |
| |
| This option makes symbolic debugging impossible. |
| |
| @item -mliw |
| @opindex mliw |
| Allow the compiler to generate @emph{Long Instruction Word} |
| instructions if the target is the @samp{AM33} or later. This is the |
| default. This option defines the preprocessor macro @samp{__LIW__}. |
| |
| @item -mnoliw |
| @opindex mnoliw |
| Do not allow the compiler to generate @emph{Long Instruction Word} |
| instructions. This option defines the preprocessor macro |
| @samp{__NO_LIW__}. |
| |
| @item -msetlb |
| @opindex msetlb |
| Allow the compiler to generate the @emph{SETLB} and @emph{Lcc} |
| instructions if the target is the @samp{AM33} or later. This is the |
| default. This option defines the preprocessor macro @samp{__SETLB__}. |
| |
| @item -mnosetlb |
| @opindex mnosetlb |
| Do not allow the compiler to generate @emph{SETLB} or @emph{Lcc} |
| instructions. This option defines the preprocessor macro |
| @samp{__NO_SETLB__}. |
| |
| @end table |
| |
| @node Moxie Options |
| @subsection Moxie Options |
| @cindex Moxie Options |
| |
| @table @gcctabopt |
| |
| @item -meb |
| @opindex meb |
| Generate big-endian code. This is the default for @samp{moxie-*-*} |
| configurations. |
| |
| @item -mel |
| @opindex mel |
| Generate little-endian code. |
| |
| @item -mno-crt0 |
| @opindex mno-crt0 |
| Do not link in the C run-time initialization object file. |
| |
| @end table |
| |
| @node PDP-11 Options |
| @subsection PDP-11 Options |
| @cindex PDP-11 Options |
| |
| These options are defined for the PDP-11: |
| |
| @table @gcctabopt |
| @item -mfpu |
| @opindex mfpu |
| Use hardware FPP floating point. This is the default. (FIS floating |
| point on the PDP-11/40 is not supported.) |
| |
| @item -msoft-float |
| @opindex msoft-float |
| Do not use hardware floating point. |
| |
| @item -mac0 |
| @opindex mac0 |
| Return floating-point results in ac0 (fr0 in Unix assembler syntax). |
| |
| @item -mno-ac0 |
| @opindex mno-ac0 |
| Return floating-point results in memory. This is the default. |
| |
| @item -m40 |
| @opindex m40 |
| Generate code for a PDP-11/40. |
| |
| @item -m45 |
| @opindex m45 |
| Generate code for a PDP-11/45. This is the default. |
| |
| @item -m10 |
| @opindex m10 |
| Generate code for a PDP-11/10. |
| |
| @item -mbcopy-builtin |
| @opindex mbcopy-builtin |
| Use inline @code{movmemhi} patterns for copying memory. This is the |
| default. |
| |
| @item -mbcopy |
| @opindex mbcopy |
| Do not use inline @code{movmemhi} patterns for copying memory. |
| |
| @item -mint16 |
| @itemx -mno-int32 |
| @opindex mint16 |
| @opindex mno-int32 |
| Use 16-bit @code{int}. This is the default. |
| |
| @item -mint32 |
| @itemx -mno-int16 |
| @opindex mint32 |
| @opindex mno-int16 |
| Use 32-bit @code{int}. |
| |
| @item -mfloat64 |
| @itemx -mno-float32 |
| @opindex mfloat64 |
| @opindex mno-float32 |
| Use 64-bit @code{float}. This is the default. |
| |
| @item -mfloat32 |
| @itemx -mno-float64 |
| @opindex mfloat32 |
| @opindex mno-float64 |
| Use 32-bit @code{float}. |
| |
| @item -mabshi |
| @opindex mabshi |
| Use @code{abshi2} pattern. This is the default. |
| |
| @item -mno-abshi |
| @opindex mno-abshi |
| Do not use @code{abshi2} pattern. |
| |
| @item -mbranch-expensive |
| @opindex mbranch-expensive |
| Pretend that branches are expensive. This is for experimenting with |
| code generation only. |
| |
| @item -mbranch-cheap |
| @opindex mbranch-cheap |
| Do not pretend that branches are expensive. This is the default. |
| |
| @item -munix-asm |
| @opindex munix-asm |
| Use Unix assembler syntax. This is the default when configured for |
| @samp{pdp11-*-bsd}. |
| |
| @item -mdec-asm |
| @opindex mdec-asm |
| Use DEC assembler syntax. This is the default when configured for any |
| PDP-11 target other than @samp{pdp11-*-bsd}. |
| @end table |
| |
| @node picoChip Options |
| @subsection picoChip Options |
| @cindex picoChip options |
| |
| These @samp{-m} options are defined for picoChip implementations: |
| |
| @table @gcctabopt |
| |
| @item -mae=@var{ae_type} |
| @opindex mcpu |
| Set the instruction set, register set, and instruction scheduling |
| parameters for array element type @var{ae_type}. Supported values |
| for @var{ae_type} are @samp{ANY}, @samp{MUL}, and @samp{MAC}. |
| |
| @option{-mae=ANY} selects a completely generic AE type. Code |
| generated with this option runs on any of the other AE types. The |
| code is not as efficient as it would be if compiled for a specific |
| AE type, and some types of operation (e.g., multiplication) do not |
| work properly on all types of AE. |
| |
| @option{-mae=MUL} selects a MUL AE type. This is the most useful AE type |
| for compiled code, and is the default. |
| |
| @option{-mae=MAC} selects a DSP-style MAC AE. Code compiled with this |
| option may suffer from poor performance of byte (char) manipulation, |
| since the DSP AE does not provide hardware support for byte load/stores. |
| |
| @item -msymbol-as-address |
| Enable the compiler to directly use a symbol name as an address in a |
| load/store instruction, without first loading it into a |
| register. Typically, the use of this option generates larger |
| programs, which run faster than when the option isn't used. However, the |
| results vary from program to program, so it is left as a user option, |
| rather than being permanently enabled. |
| |
| @item -mno-inefficient-warnings |
| Disables warnings about the generation of inefficient code. These |
| warnings can be generated, for example, when compiling code that |
| performs byte-level memory operations on the MAC AE type. The MAC AE has |
| no hardware support for byte-level memory operations, so all byte |
| load/stores must be synthesized from word load/store operations. This is |
| inefficient and a warning is generated to indicate |
| that you should rewrite the code to avoid byte operations, or to target |
| an AE type that has the necessary hardware support. This option disables |
| these warnings. |
| |
| @end table |
| |
| @node PowerPC Options |
| @subsection PowerPC Options |
| @cindex PowerPC options |
| |
| These are listed under @xref{RS/6000 and PowerPC Options}. |
| |
| @node RL78 Options |
| @subsection RL78 Options |
| @cindex RL78 Options |
| |
| @table @gcctabopt |
| |
| @item -msim |
| @opindex msim |
| Links in additional target libraries to support operation within a |
| simulator. |
| |
| @item -mmul=none |
| @itemx -mmul=g13 |
| @itemx -mmul=rl78 |
| @opindex mmul |
| Specifies the type of hardware multiplication support to be used. The |
| default is @code{none}, which uses software multiplication functions. |
| The @code{g13} option is for the hardware multiply/divide peripheral |
| only on the RL78/G13 targets. The @code{rl78} option is for the |
| standard hardware multiplication defined in the RL78 software manual. |
| |
| @end table |
| |
| @node RS/6000 and PowerPC Options |
| @subsection IBM RS/6000 and PowerPC Options |
| @cindex RS/6000 and PowerPC Options |
| @cindex IBM RS/6000 and PowerPC Options |
| |
| These @samp{-m} options are defined for the IBM RS/6000 and PowerPC: |
| @table @gcctabopt |
| @item -mpowerpc-gpopt |
| @itemx -mno-powerpc-gpopt |
| @itemx -mpowerpc-gfxopt |
| @itemx -mno-powerpc-gfxopt |
| @need 800 |
| @itemx -mpowerpc64 |
| @itemx -mno-powerpc64 |
| @itemx -mmfcrf |
| @itemx -mno-mfcrf |
| @itemx -mpopcntb |
| @itemx -mno-popcntb |
| @itemx -mpopcntd |
| @itemx -mno-popcntd |
| @itemx -mfprnd |
| @itemx -mno-fprnd |
| @need 800 |
| @itemx -mcmpb |
| @itemx -mno-cmpb |
| @itemx -mmfpgpr |
| @itemx -mno-mfpgpr |
| @itemx -mhard-dfp |
| @itemx -mno-hard-dfp |
| @opindex mpowerpc-gpopt |
| @opindex mno-powerpc-gpopt |
| @opindex mpowerpc-gfxopt |
| @opindex mno-powerpc-gfxopt |
| @opindex mpowerpc64 |
| @opindex mno-powerpc64 |
| @opindex mmfcrf |
| @opindex mno-mfcrf |
| @opindex mpopcntb |
| @opindex mno-popcntb |
| @opindex mpopcntd |
| @opindex mno-popcntd |
| @opindex mfprnd |
| @opindex mno-fprnd |
| @opindex mcmpb |
| @opindex mno-cmpb |
| @opindex mmfpgpr |
| @opindex mno-mfpgpr |
| @opindex mhard-dfp |
| @opindex mno-hard-dfp |
| You use these options to specify which instructions are available on the |
| processor you are using. The default value of these options is |
| determined when configuring GCC@. Specifying the |
| @option{-mcpu=@var{cpu_type}} overrides the specification of these |
| options. We recommend you use the @option{-mcpu=@var{cpu_type}} option |
| rather than the options listed above. |
| |
| Specifying @option{-mpowerpc-gpopt} allows |
| GCC to use the optional PowerPC architecture instructions in the |
| General Purpose group, including floating-point square root. Specifying |
| @option{-mpowerpc-gfxopt} allows GCC to |
| use the optional PowerPC architecture instructions in the Graphics |
| group, including floating-point select. |
| |
| The @option{-mmfcrf} option allows GCC to generate the move from |
| condition register field instruction implemented on the POWER4 |
| processor and other processors that support the PowerPC V2.01 |
| architecture. |
| The @option{-mpopcntb} option allows GCC to generate the popcount and |
| double-precision FP reciprocal estimate instruction implemented on the |
| POWER5 processor and other processors that support the PowerPC V2.02 |
| architecture. |
| The @option{-mpopcntd} option allows GCC to generate the popcount |
| instruction implemented on the POWER7 processor and other processors |
| that support the PowerPC V2.06 architecture. |
| The @option{-mfprnd} option allows GCC to generate the FP round to |
| integer instructions implemented on the POWER5+ processor and other |
| processors that support the PowerPC V2.03 architecture. |
| The @option{-mcmpb} option allows GCC to generate the compare bytes |
| instruction implemented on the POWER6 processor and other processors |
| that support the PowerPC V2.05 architecture. |
| The @option{-mmfpgpr} option allows GCC to generate the FP move to/from |
| general-purpose register instructions implemented on the POWER6X |
| processor and other processors that support the extended PowerPC V2.05 |
| architecture. |
| The @option{-mhard-dfp} option allows GCC to generate the decimal |
| floating-point instructions implemented on some POWER processors. |
| |
| The @option{-mpowerpc64} option allows GCC to generate the additional |
| 64-bit instructions that are found in the full PowerPC64 architecture |
| and to treat GPRs as 64-bit, doubleword quantities. GCC defaults to |
| @option{-mno-powerpc64}. |
| |
| @item -mcpu=@var{cpu_type} |
| @opindex mcpu |
| Set architecture type, register usage, and |
| instruction scheduling parameters for machine type @var{cpu_type}. |
| Supported values for @var{cpu_type} are @samp{401}, @samp{403}, |
| @samp{405}, @samp{405fp}, @samp{440}, @samp{440fp}, @samp{464}, @samp{464fp}, |
| @samp{476}, @samp{476fp}, @samp{505}, @samp{601}, @samp{602}, @samp{603}, |
| @samp{603e}, @samp{604}, @samp{604e}, @samp{620}, @samp{630}, @samp{740}, |
| @samp{7400}, @samp{7450}, @samp{750}, @samp{801}, @samp{821}, @samp{823}, |
| @samp{860}, @samp{970}, @samp{8540}, @samp{a2}, @samp{e300c2}, |
| @samp{e300c3}, @samp{e500mc}, @samp{e500mc64}, @samp{e5500}, |
| @samp{e6500}, @samp{ec603e}, @samp{G3}, @samp{G4}, @samp{G5}, |
| @samp{titan}, @samp{power3}, @samp{power4}, @samp{power5}, @samp{power5+}, |
| @samp{power6}, @samp{power6x}, @samp{power7}, @samp{powerpc}, |
| @samp{powerpc64}, and @samp{rs64}. |
| |
| @option{-mcpu=powerpc}, and @option{-mcpu=powerpc64} specify pure 32-bit |
| PowerPC and 64-bit PowerPC architecture machine |
| types, with an appropriate, generic processor model assumed for |
| scheduling purposes. |
| |
| The other options specify a specific processor. Code generated under |
| those options runs best on that processor, and may not run at all on |
| others. |
| |
| The @option{-mcpu} options automatically enable or disable the |
| following options: |
| |
| @gccoptlist{-maltivec -mfprnd -mhard-float -mmfcrf -mmultiple @gol |
| -mpopcntb -mpopcntd -mpowerpc64 @gol |
| -mpowerpc-gpopt -mpowerpc-gfxopt -msingle-float -mdouble-float @gol |
| -msimple-fpu -mstring -mmulhw -mdlmzb -mmfpgpr -mvsx} |
| |
| The particular options set for any particular CPU varies between |
| compiler versions, depending on what setting seems to produce optimal |
| code for that CPU; it doesn't necessarily reflect the actual hardware's |
| capabilities. If you wish to set an individual option to a particular |
| value, you may specify it after the @option{-mcpu} option, like |
| @option{-mcpu=970 -mno-altivec}. |
| |
| On AIX, the @option{-maltivec} and @option{-mpowerpc64} options are |
| not enabled or disabled by the @option{-mcpu} option at present because |
| AIX does not have full support for these options. You may still |
| enable or disable them individually if you're sure it'll work in your |
| environment. |
| |
| @item -mtune=@var{cpu_type} |
| @opindex mtune |
| Set the instruction scheduling parameters for machine type |
| @var{cpu_type}, but do not set the architecture type or register usage, |
| as @option{-mcpu=@var{cpu_type}} does. The same |
| values for @var{cpu_type} are used for @option{-mtune} as for |
| @option{-mcpu}. If both are specified, the code generated uses the |
| architecture and registers set by @option{-mcpu}, but the |
| scheduling parameters set by @option{-mtune}. |
| |
| @item -mcmodel=small |
| @opindex mcmodel=small |
| Generate PowerPC64 code for the small model: The TOC is limited to |
| 64k. |
| |
| @item -mcmodel=medium |
| @opindex mcmodel=medium |
| Generate PowerPC64 code for the medium model: The TOC and other static |
| data may be up to a total of 4G in size. |
| |
| @item -mcmodel=large |
| @opindex mcmodel=large |
| Generate PowerPC64 code for the large model: The TOC may be up to 4G |
| in size. Other data and code is only limited by the 64-bit address |
| space. |
| |
| @item -maltivec |
| @itemx -mno-altivec |
| @opindex maltivec |
| @opindex mno-altivec |
| Generate code that uses (does not use) AltiVec instructions, and also |
| enable the use of built-in functions that allow more direct access to |
| the AltiVec instruction set. You may also need to set |
| @option{-mabi=altivec} to adjust the current ABI with AltiVec ABI |
| enhancements. |
| |
| @item -mvrsave |
| @itemx -mno-vrsave |
| @opindex mvrsave |
| @opindex mno-vrsave |
| Generate VRSAVE instructions when generating AltiVec code. |
| |
| @item -mgen-cell-microcode |
| @opindex mgen-cell-microcode |
| Generate Cell microcode instructions. |
| |
| @item -mwarn-cell-microcode |
| @opindex mwarn-cell-microcode |
| Warn when a Cell microcode instruction is emitted. An example |
| of a Cell microcode instruction is a variable shift. |
| |
| @item -msecure-plt |
| @opindex msecure-plt |
| Generate code that allows @command{ld} and @command{ld.so} |
| to build executables and shared |
| libraries with non-executable @code{.plt} and @code{.got} sections. |
| This is a PowerPC |
| 32-bit SYSV ABI option. |
| |
| @item -mbss-plt |
| @opindex mbss-plt |
| Generate code that uses a BSS @code{.plt} section that @command{ld.so} |
| fills in, and |
| requires @code{.plt} and @code{.got} |
| sections that are both writable and executable. |
| This is a PowerPC 32-bit SYSV ABI option. |
| |
| @item -misel |
| @itemx -mno-isel |
| @opindex misel |
| @opindex mno-isel |
| This switch enables or disables the generation of ISEL instructions. |
| |
| @item -misel=@var{yes/no} |
| This switch has been deprecated. Use @option{-misel} and |
| @option{-mno-isel} instead. |
| |
| @item -mspe |
| @itemx -mno-spe |
| @opindex mspe |
| @opindex mno-spe |
| This switch enables or disables the generation of SPE simd |
| instructions. |
| |
| @item -mpaired |
| @itemx -mno-paired |
| @opindex mpaired |
| @opindex mno-paired |
| This switch enables or disables the generation of PAIRED simd |
| instructions. |
| |
| @item -mspe=@var{yes/no} |
| This option has been deprecated. Use @option{-mspe} and |
| @option{-mno-spe} instead. |
| |
| @item -mvsx |
| @itemx -mno-vsx |
| @opindex mvsx |
| @opindex mno-vsx |
| Generate code that uses (does not use) vector/scalar (VSX) |
| instructions, and also enable the use of built-in functions that allow |
| more direct access to the VSX instruction set. |
| |
| @item -mfloat-gprs=@var{yes/single/double/no} |
| @itemx -mfloat-gprs |
| @opindex mfloat-gprs |
| This switch enables or disables the generation of floating-point |
| operations on the general-purpose registers for architectures that |
| support it. |
| |
| The argument @var{yes} or @var{single} enables the use of |
| single-precision floating-point operations. |
| |
| The argument @var{double} enables the use of single and |
| double-precision floating-point operations. |
| |
| The argument @var{no} disables floating-point operations on the |
| general-purpose registers. |
| |
| This option is currently only available on the MPC854x. |
| |
| @item -m32 |
| @itemx -m64 |
| @opindex m32 |
| @opindex m64 |
| Generate code for 32-bit or 64-bit environments of Darwin and SVR4 |
| targets (including GNU/Linux). The 32-bit environment sets int, long |
| and pointer to 32 bits and generates code that runs on any PowerPC |
| variant. The 64-bit environment sets int to 32 bits and long and |
| pointer to 64 bits, and generates code for PowerPC64, as for |
| @option{-mpowerpc64}. |
| |
| @item -mfull-toc |
| @itemx -mno-fp-in-toc |
| @itemx -mno-sum-in-toc |
| @itemx -mminimal-toc |
| @opindex mfull-toc |
| @opindex mno-fp-in-toc |
| @opindex mno-sum-in-toc |
| @opindex mminimal-toc |
| Modify generation of the TOC (Table Of Contents), which is created for |
| every executable file. The @option{-mfull-toc} option is selected by |
| default. In that case, GCC allocates at least one TOC entry for |
| each unique non-automatic variable reference in your program. GCC |
| also places floating-point constants in the TOC@. However, only |
| 16,384 entries are available in the TOC@. |
| |
| If you receive a linker error message that saying you have overflowed |
| the available TOC space, you can reduce the amount of TOC space used |
| with the @option{-mno-fp-in-toc} and @option{-mno-sum-in-toc} options. |
| @option{-mno-fp-in-toc} prevents GCC from putting floating-point |
| constants in the TOC and @option{-mno-sum-in-toc} forces GCC to |
| generate code to calculate the sum of an address and a constant at |
| run time instead of putting that sum into the TOC@. You may specify one |
| or both of these options. Each causes GCC to produce very slightly |
| slower and larger code at the expense of conserving TOC space. |
| |
| If you still run out of space in the TOC even when you specify both of |
| these options, specify @option{-mminimal-toc} instead. This option causes |
| GCC to make only one TOC entry for every file. When you specify this |
| option, GCC produces code that is slower and larger but which |
| uses extremely little TOC space. You may wish to use this option |
| only on files that contain less frequently-executed code. |
| |
| @item -maix64 |
| @itemx -maix32 |
| @opindex maix64 |
| @opindex maix32 |
| Enable 64-bit AIX ABI and calling convention: 64-bit pointers, 64-bit |
| @code{long} type, and the infrastructure needed to support them. |
| Specifying @option{-maix64} implies @option{-mpowerpc64}, |
| while @option{-maix32} disables the 64-bit ABI and |
| implies @option{-mno-powerpc64}. GCC defaults to @option{-maix32}. |
| |
| @item -mxl-compat |
| @itemx -mno-xl-compat |
| @opindex mxl-compat |
| @opindex mno-xl-compat |
| Produce code that conforms more closely to IBM XL compiler semantics |
| when using AIX-compatible ABI@. Pass floating-point arguments to |
| prototyped functions beyond the register save area (RSA) on the stack |
| in addition to argument FPRs. Do not assume that most significant |
| double in 128-bit long double value is properly rounded when comparing |
| values and converting to double. Use XL symbol names for long double |
| support routines. |
| |
| The AIX calling convention was extended but not initially documented to |
| handle an obscure K&R C case of calling a function that takes the |
| address of its arguments with fewer arguments than declared. IBM XL |
| compilers access floating-point arguments that do not fit in the |
| RSA from the stack when a subroutine is compiled without |
| optimization. Because always storing floating-point arguments on the |
| stack is inefficient and rarely needed, this option is not enabled by |
| default and only is necessary when calling subroutines compiled by IBM |
| XL compilers without optimization. |
| |
| @item -mpe |
| @opindex mpe |
| Support @dfn{IBM RS/6000 SP} @dfn{Parallel Environment} (PE)@. Link an |
| application written to use message passing with special startup code to |
| enable the application to run. The system must have PE installed in the |
| standard location (@file{/usr/lpp/ppe.poe/}), or the @file{specs} file |
| must be overridden with the @option{-specs=} option to specify the |
| appropriate directory location. The Parallel Environment does not |
| support threads, so the @option{-mpe} option and the @option{-pthread} |
| option are incompatible. |
| |
| @item -malign-natural |
| @itemx -malign-power |
| @opindex malign-natural |
| @opindex malign-power |
| On AIX, 32-bit Darwin, and 64-bit PowerPC GNU/Linux, the option |
| @option{-malign-natural} overrides the ABI-defined alignment of larger |
| types, such as floating-point doubles, on their natural size-based boundary. |
| The option @option{-malign-power} instructs GCC to follow the ABI-specified |
| alignment rules. GCC defaults to the standard alignment defined in the ABI@. |
| |
| On 64-bit Darwin, natural alignment is the default, and @option{-malign-power} |
| is not supported. |
| |
| @item -msoft-float |
| @itemx -mhard-float |
| @opindex msoft-float |
| @opindex mhard-float |
| Generate code that does not use (uses) the floating-point register set. |
| Software floating-point emulation is provided if you use the |
| @option{-msoft-float} option, and pass the option to GCC when linking. |
| |
| @item -msingle-float |
| @itemx -mdouble-float |
| @opindex msingle-float |
| @opindex mdouble-float |
| Generate code for single- or double-precision floating-point operations. |
| @option{-mdouble-float} implies @option{-msingle-float}. |
| |
| @item -msimple-fpu |
| @opindex msimple-fpu |
| Do not generate @code{sqrt} and @code{div} instructions for hardware |
| floating-point unit. |
| |
| @item -mfpu=@var{name} |
| @opindex mfpu |
| Specify type of floating-point unit. Valid values for @var{name} are |
| @samp{sp_lite} (equivalent to @option{-msingle-float -msimple-fpu}), |
| @samp{dp_lite} (equivalent to @option{-mdouble-float -msimple-fpu}), |
| @samp{sp_full} (equivalent to @option{-msingle-float}), |
| and @samp{dp_full} (equivalent to @option{-mdouble-float}). |
| |
| @item -mxilinx-fpu |
| @opindex mxilinx-fpu |
| Perform optimizations for the floating-point unit on Xilinx PPC 405/440. |
| |
| @item -mmultiple |
| @itemx -mno-multiple |
| @opindex mmultiple |
| @opindex mno-multiple |
| Generate code that uses (does not use) the load multiple word |
| instructions and the store multiple word instructions. These |
| instructions are generated by default on POWER systems, and not |
| generated on PowerPC systems. Do not use @option{-mmultiple} on little-endian |
| PowerPC systems, since those instructions do not work when the |
| processor is in little-endian mode. The exceptions are PPC740 and |
| PPC750 which permit these instructions in little-endian mode. |
| |
| @item -mstring |
| @itemx -mno-string |
| @opindex mstring |
| @opindex mno-string |
| Generate code that uses (does not use) the load string instructions |
| and the store string word instructions to save multiple registers and |
| do small block moves. These instructions are generated by default on |
| POWER systems, and not generated on PowerPC systems. Do not use |
| @option{-mstring} on little-endian PowerPC systems, since those |
| instructions do not work when the processor is in little-endian mode. |
| The exceptions are PPC740 and PPC750 which permit these instructions |
| in little-endian mode. |
| |
| @item -mupdate |
| @itemx -mno-update |
| @opindex mupdate |
| @opindex mno-update |
| Generate code that uses (does not use) the load or store instructions |
| that update the base register to the address of the calculated memory |
| location. These instructions are generated by default. If you use |
| @option{-mno-update}, there is a small window between the time that the |
| stack pointer is updated and the address of the previous frame is |
| stored, which means code that walks the stack frame across interrupts or |
| signals may get corrupted data. |
| |
| @item -mavoid-indexed-addresses |
| @itemx -mno-avoid-indexed-addresses |
| @opindex mavoid-indexed-addresses |
| @opindex mno-avoid-indexed-addresses |
| Generate code that tries to avoid (not avoid) the use of indexed load |
| or store instructions. These instructions can incur a performance |
| penalty on Power6 processors in certain situations, such as when |
| stepping through large arrays that cross a 16M boundary. This option |
| is enabled by default when targeting Power6 and disabled otherwise. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Generate code that uses (does not use) the floating-point multiply and |
| accumulate instructions. These instructions are generated by default |
| if hardware floating point is used. The machine-dependent |
| @option{-mfused-madd} option is now mapped to the machine-independent |
| @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is |
| mapped to @option{-ffp-contract=off}. |
| |
| @item -mmulhw |
| @itemx -mno-mulhw |
| @opindex mmulhw |
| @opindex mno-mulhw |
| Generate code that uses (does not use) the half-word multiply and |
| multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors. |
| These instructions are generated by default when targeting those |
| processors. |
| |
| @item -mdlmzb |
| @itemx -mno-dlmzb |
| @opindex mdlmzb |
| @opindex mno-dlmzb |
| Generate code that uses (does not use) the string-search @samp{dlmzb} |
| instruction on the IBM 405, 440, 464 and 476 processors. This instruction is |
| generated by default when targeting those processors. |
| |
| @item -mno-bit-align |
| @itemx -mbit-align |
| @opindex mno-bit-align |
| @opindex mbit-align |
| On System V.4 and embedded PowerPC systems do not (do) force structures |
| and unions that contain bit-fields to be aligned to the base type of the |
| bit-field. |
| |
| For example, by default a structure containing nothing but 8 |
| @code{unsigned} bit-fields of length 1 is aligned to a 4-byte |
| boundary and has a size of 4 bytes. By using @option{-mno-bit-align}, |
| the structure is aligned to a 1-byte boundary and is 1 byte in |
| size. |
| |
| @item -mno-strict-align |
| @itemx -mstrict-align |
| @opindex mno-strict-align |
| @opindex mstrict-align |
| On System V.4 and embedded PowerPC systems do not (do) assume that |
| unaligned memory references are handled by the system. |
| |
| @item -mrelocatable |
| @itemx -mno-relocatable |
| @opindex mrelocatable |
| @opindex mno-relocatable |
| Generate code that allows (does not allow) a static executable to be |
| relocated to a different address at run time. A simple embedded |
| PowerPC system loader should relocate the entire contents of |
| @code{.got2} and 4-byte locations listed in the @code{.fixup} section, |
| a table of 32-bit addresses generated by this option. For this to |
| work, all objects linked together must be compiled with |
| @option{-mrelocatable} or @option{-mrelocatable-lib}. |
| @option{-mrelocatable} code aligns the stack to an 8-byte boundary. |
| |
| @item -mrelocatable-lib |
| @itemx -mno-relocatable-lib |
| @opindex mrelocatable-lib |
| @opindex mno-relocatable-lib |
| Like @option{-mrelocatable}, @option{-mrelocatable-lib} generates a |
| @code{.fixup} section to allow static executables to be relocated at |
| run time, but @option{-mrelocatable-lib} does not use the smaller stack |
| alignment of @option{-mrelocatable}. Objects compiled with |
| @option{-mrelocatable-lib} may be linked with objects compiled with |
| any combination of the @option{-mrelocatable} options. |
| |
| @item -mno-toc |
| @itemx -mtoc |
| @opindex mno-toc |
| @opindex mtoc |
| On System V.4 and embedded PowerPC systems do not (do) assume that |
| register 2 contains a pointer to a global area pointing to the addresses |
| used in the program. |
| |
| @item -mlittle |
| @itemx -mlittle-endian |
| @opindex mlittle |
| @opindex mlittle-endian |
| On System V.4 and embedded PowerPC systems compile code for the |
| processor in little-endian mode. The @option{-mlittle-endian} option is |
| the same as @option{-mlittle}. |
| |
| @item -mbig |
| @itemx -mbig-endian |
| @opindex mbig |
| @opindex mbig-endian |
| On System V.4 and embedded PowerPC systems compile code for the |
| processor in big-endian mode. The @option{-mbig-endian} option is |
| the same as @option{-mbig}. |
| |
| @item -mdynamic-no-pic |
| @opindex mdynamic-no-pic |
| On Darwin and Mac OS X systems, compile code so that it is not |
| relocatable, but that its external references are relocatable. The |
| resulting code is suitable for applications, but not shared |
| libraries. |
| |
| @item -msingle-pic-base |
| @opindex msingle-pic-base |
| Treat the register used for PIC addressing as read-only, rather than |
| loading it in the prologue for each function. The runtime system is |
| responsible for initializing this register with an appropriate value |
| before execution begins. |
| |
| @item -mprioritize-restricted-insns=@var{priority} |
| @opindex mprioritize-restricted-insns |
| This option controls the priority that is assigned to |
| dispatch-slot restricted instructions during the second scheduling |
| pass. The argument @var{priority} takes the value @samp{0}, @samp{1}, |
| or @samp{2} to assign no, highest, or second-highest (respectively) |
| priority to dispatch-slot restricted |
| instructions. |
| |
| @item -msched-costly-dep=@var{dependence_type} |
| @opindex msched-costly-dep |
| This option controls which dependences are considered costly |
| by the target during instruction scheduling. The argument |
| @var{dependence_type} takes one of the following values: |
| |
| @table @asis |
| @item @samp{no} |
| No dependence is costly. |
| |
| @item @samp{all} |
| All dependences are costly. |
| |
| @item @samp{true_store_to_load} |
| A true dependence from store to load is costly. |
| |
| @item @samp{store_to_load} |
| Any dependence from store to load is costly. |
| |
| @item @var{number} |
| Any dependence for which the latency is greater than or equal to |
| @var{number} is costly. |
| @end table |
| |
| @item -minsert-sched-nops=@var{scheme} |
| @opindex minsert-sched-nops |
| This option controls which NOP insertion scheme is used during |
| the second scheduling pass. The argument @var{scheme} takes one of the |
| following values: |
| |
| @table @asis |
| @item @samp{no} |
| Don't insert NOPs. |
| |
| @item @samp{pad} |
| Pad with NOPs any dispatch group that has vacant issue slots, |
| according to the scheduler's grouping. |
| |
| @item @samp{regroup_exact} |
| Insert NOPs to force costly dependent insns into |
| separate groups. Insert exactly as many NOPs as needed to force an insn |
| to a new group, according to the estimated processor grouping. |
| |
| @item @var{number} |
| Insert NOPs to force costly dependent insns into |
| separate groups. Insert @var{number} NOPs to force an insn to a new group. |
| @end table |
| |
| @item -mcall-sysv |
| @opindex mcall-sysv |
| On System V.4 and embedded PowerPC systems compile code using calling |
| conventions that adhere to the March 1995 draft of the System V |
| Application Binary Interface, PowerPC processor supplement. This is the |
| default unless you configured GCC using @samp{powerpc-*-eabiaix}. |
| |
| @item -mcall-sysv-eabi |
| @itemx -mcall-eabi |
| @opindex mcall-sysv-eabi |
| @opindex mcall-eabi |
| Specify both @option{-mcall-sysv} and @option{-meabi} options. |
| |
| @item -mcall-sysv-noeabi |
| @opindex mcall-sysv-noeabi |
| Specify both @option{-mcall-sysv} and @option{-mno-eabi} options. |
| |
| @item -mcall-aixdesc |
| @opindex m |
| On System V.4 and embedded PowerPC systems compile code for the AIX |
| operating system. |
| |
| @item -mcall-linux |
| @opindex mcall-linux |
| On System V.4 and embedded PowerPC systems compile code for the |
| Linux-based GNU system. |
| |
| @item -mcall-freebsd |
| @opindex mcall-freebsd |
| On System V.4 and embedded PowerPC systems compile code for the |
| FreeBSD operating system. |
| |
| @item -mcall-netbsd |
| @opindex mcall-netbsd |
| On System V.4 and embedded PowerPC systems compile code for the |
| NetBSD operating system. |
| |
| @item -mcall-openbsd |
| @opindex mcall-netbsd |
| On System V.4 and embedded PowerPC systems compile code for the |
| OpenBSD operating system. |
| |
| @item -maix-struct-return |
| @opindex maix-struct-return |
| Return all structures in memory (as specified by the AIX ABI)@. |
| |
| @item -msvr4-struct-return |
| @opindex msvr4-struct-return |
| Return structures smaller than 8 bytes in registers (as specified by the |
| SVR4 ABI)@. |
| |
| @item -mabi=@var{abi-type} |
| @opindex mabi |
| Extend the current ABI with a particular extension, or remove such extension. |
| Valid values are @var{altivec}, @var{no-altivec}, @var{spe}, |
| @var{no-spe}, @var{ibmlongdouble}, @var{ieeelongdouble}@. |
| |
| @item -mabi=spe |
| @opindex mabi=spe |
| Extend the current ABI with SPE ABI extensions. This does not change |
| the default ABI, instead it adds the SPE ABI extensions to the current |
| ABI@. |
| |
| @item -mabi=no-spe |
| @opindex mabi=no-spe |
| Disable Book-E SPE ABI extensions for the current ABI@. |
| |
| @item -mabi=ibmlongdouble |
| @opindex mabi=ibmlongdouble |
| Change the current ABI to use IBM extended-precision long double. |
| This is a PowerPC 32-bit SYSV ABI option. |
| |
| @item -mabi=ieeelongdouble |
| @opindex mabi=ieeelongdouble |
| Change the current ABI to use IEEE extended-precision long double. |
| This is a PowerPC 32-bit Linux ABI option. |
| |
| @item -mprototype |
| @itemx -mno-prototype |
| @opindex mprototype |
| @opindex mno-prototype |
| On System V.4 and embedded PowerPC systems assume that all calls to |
| variable argument functions are properly prototyped. Otherwise, the |
| compiler must insert an instruction before every non-prototyped call to |
| set or clear bit 6 of the condition code register (@var{CR}) to |
| indicate whether floating-point values are passed in the floating-point |
| registers in case the function takes variable arguments. With |
| @option{-mprototype}, only calls to prototyped variable argument functions |
| set or clear the bit. |
| |
| @item -msim |
| @opindex msim |
| On embedded PowerPC systems, assume that the startup module is called |
| @file{sim-crt0.o} and that the standard C libraries are @file{libsim.a} and |
| @file{libc.a}. This is the default for @samp{powerpc-*-eabisim} |
| configurations. |
| |
| @item -mmvme |
| @opindex mmvme |
| On embedded PowerPC systems, assume that the startup module is called |
| @file{crt0.o} and the standard C libraries are @file{libmvme.a} and |
| @file{libc.a}. |
| |
| @item -mads |
| @opindex mads |
| On embedded PowerPC systems, assume that the startup module is called |
| @file{crt0.o} and the standard C libraries are @file{libads.a} and |
| @file{libc.a}. |
| |
| @item -myellowknife |
| @opindex myellowknife |
| On embedded PowerPC systems, assume that the startup module is called |
| @file{crt0.o} and the standard C libraries are @file{libyk.a} and |
| @file{libc.a}. |
| |
| @item -mvxworks |
| @opindex mvxworks |
| On System V.4 and embedded PowerPC systems, specify that you are |
| compiling for a VxWorks system. |
| |
| @item -memb |
| @opindex memb |
| On embedded PowerPC systems, set the @var{PPC_EMB} bit in the ELF flags |
| header to indicate that @samp{eabi} extended relocations are used. |
| |
| @item -meabi |
| @itemx -mno-eabi |
| @opindex meabi |
| @opindex mno-eabi |
| On System V.4 and embedded PowerPC systems do (do not) adhere to the |
| Embedded Applications Binary Interface (EABI), which is a set of |
| modifications to the System V.4 specifications. Selecting @option{-meabi} |
| means that the stack is aligned to an 8-byte boundary, a function |
| @code{__eabi} is called from @code{main} to set up the EABI |
| environment, and the @option{-msdata} option can use both @code{r2} and |
| @code{r13} to point to two separate small data areas. Selecting |
| @option{-mno-eabi} means that the stack is aligned to a 16-byte boundary, |
| no EABI initialization function is called from @code{main}, and the |
| @option{-msdata} option only uses @code{r13} to point to a single |
| small data area. The @option{-meabi} option is on by default if you |
| configured GCC using one of the @samp{powerpc*-*-eabi*} options. |
| |
| @item -msdata=eabi |
| @opindex msdata=eabi |
| On System V.4 and embedded PowerPC systems, put small initialized |
| @code{const} global and static data in the @samp{.sdata2} section, which |
| is pointed to by register @code{r2}. Put small initialized |
| non-@code{const} global and static data in the @samp{.sdata} section, |
| which is pointed to by register @code{r13}. Put small uninitialized |
| global and static data in the @samp{.sbss} section, which is adjacent to |
| the @samp{.sdata} section. The @option{-msdata=eabi} option is |
| incompatible with the @option{-mrelocatable} option. The |
| @option{-msdata=eabi} option also sets the @option{-memb} option. |
| |
| @item -msdata=sysv |
| @opindex msdata=sysv |
| On System V.4 and embedded PowerPC systems, put small global and static |
| data in the @samp{.sdata} section, which is pointed to by register |
| @code{r13}. Put small uninitialized global and static data in the |
| @samp{.sbss} section, which is adjacent to the @samp{.sdata} section. |
| The @option{-msdata=sysv} option is incompatible with the |
| @option{-mrelocatable} option. |
| |
| @item -msdata=default |
| @itemx -msdata |
| @opindex msdata=default |
| @opindex msdata |
| On System V.4 and embedded PowerPC systems, if @option{-meabi} is used, |
| compile code the same as @option{-msdata=eabi}, otherwise compile code the |
| same as @option{-msdata=sysv}. |
| |
| @item -msdata=data |
| @opindex msdata=data |
| On System V.4 and embedded PowerPC systems, put small global |
| data in the @samp{.sdata} section. Put small uninitialized global |
| data in the @samp{.sbss} section. Do not use register @code{r13} |
| to address small data however. This is the default behavior unless |
| other @option{-msdata} options are used. |
| |
| @item -msdata=none |
| @itemx -mno-sdata |
| @opindex msdata=none |
| @opindex mno-sdata |
| On embedded PowerPC systems, put all initialized global and static data |
| in the @samp{.data} section, and all uninitialized data in the |
| @samp{.bss} section. |
| |
| @item -mblock-move-inline-limit=@var{num} |
| @opindex mblock-move-inline-limit |
| Inline all block moves (such as calls to @code{memcpy} or structure |
| copies) less than or equal to @var{num} bytes. The minimum value for |
| @var{num} is 32 bytes on 32-bit targets and 64 bytes on 64-bit |
| targets. The default value is target-specific. |
| |
| @item -G @var{num} |
| @opindex G |
| @cindex smaller data references (PowerPC) |
| @cindex .sdata/.sdata2 references (PowerPC) |
| On embedded PowerPC systems, put global and static items less than or |
| equal to @var{num} bytes into the small data or BSS sections instead of |
| the normal data or BSS section. By default, @var{num} is 8. The |
| @option{-G @var{num}} switch is also passed to the linker. |
| All modules should be compiled with the same @option{-G @var{num}} value. |
| |
| @item -mregnames |
| @itemx -mno-regnames |
| @opindex mregnames |
| @opindex mno-regnames |
| On System V.4 and embedded PowerPC systems do (do not) emit register |
| names in the assembly language output using symbolic forms. |
| |
| @item -mlongcall |
| @itemx -mno-longcall |
| @opindex mlongcall |
| @opindex mno-longcall |
| By default assume that all calls are far away so that a longer and more |
| expensive calling sequence is required. This is required for calls |
| farther than 32 megabytes (33,554,432 bytes) from the current location. |
| A short call is generated if the compiler knows |
| the call cannot be that far away. This setting can be overridden by |
| the @code{shortcall} function attribute, or by @code{#pragma |
| longcall(0)}. |
| |
| Some linkers are capable of detecting out-of-range calls and generating |
| glue code on the fly. On these systems, long calls are unnecessary and |
| generate slower code. As of this writing, the AIX linker can do this, |
| as can the GNU linker for PowerPC/64. It is planned to add this feature |
| to the GNU linker for 32-bit PowerPC systems as well. |
| |
| On Darwin/PPC systems, @code{#pragma longcall} generates @code{jbsr |
| callee, L42}, plus a @dfn{branch island} (glue code). The two target |
| addresses represent the callee and the branch island. The |
| Darwin/PPC linker prefers the first address and generates a @code{bl |
| callee} if the PPC @code{bl} instruction reaches the callee directly; |
| otherwise, the linker generates @code{bl L42} to call the branch |
| island. The branch island is appended to the body of the |
| calling function; it computes the full 32-bit address of the callee |
| and jumps to it. |
| |
| On Mach-O (Darwin) systems, this option directs the compiler emit to |
| the glue for every direct call, and the Darwin linker decides whether |
| to use or discard it. |
| |
| In the future, GCC may ignore all longcall specifications |
| when the linker is known to generate glue. |
| |
| @item -mtls-markers |
| @itemx -mno-tls-markers |
| @opindex mtls-markers |
| @opindex mno-tls-markers |
| Mark (do not mark) calls to @code{__tls_get_addr} with a relocation |
| specifying the function argument. The relocation allows the linker to |
| reliably associate function call with argument setup instructions for |
| TLS optimization, which in turn allows GCC to better schedule the |
| sequence. |
| |
| @item -pthread |
| @opindex pthread |
| Adds support for multithreading with the @dfn{pthreads} library. |
| This option sets flags for both the preprocessor and linker. |
| |
| @item -mrecip |
| @itemx -mno-recip |
| @opindex mrecip |
| This option enables use of the reciprocal estimate and |
| reciprocal square root estimate instructions with additional |
| Newton-Raphson steps to increase precision instead of doing a divide or |
| square root and divide for floating-point arguments. You should use |
| the @option{-ffast-math} option when using @option{-mrecip} (or at |
| least @option{-funsafe-math-optimizations}, |
| @option{-finite-math-only}, @option{-freciprocal-math} and |
| @option{-fno-trapping-math}). Note that while the throughput of the |
| sequence is generally higher than the throughput of the non-reciprocal |
| instruction, the precision of the sequence can be decreased by up to 2 |
| ulp (i.e.@: the inverse of 1.0 equals 0.99999994) for reciprocal square |
| roots. |
| |
| @item -mrecip=@var{opt} |
| @opindex mrecip=opt |
| This option controls which reciprocal estimate instructions |
| may be used. @var{opt} is a comma-separated list of options, which may |
| be preceded by a @code{!} to invert the option: |
| @code{all}: enable all estimate instructions, |
| @code{default}: enable the default instructions, equivalent to @option{-mrecip}, |
| @code{none}: disable all estimate instructions, equivalent to @option{-mno-recip}; |
| @code{div}: enable the reciprocal approximation instructions for both single and double precision; |
| @code{divf}: enable the single-precision reciprocal approximation instructions; |
| @code{divd}: enable the double-precision reciprocal approximation instructions; |
| @code{rsqrt}: enable the reciprocal square root approximation instructions for both single and double precision; |
| @code{rsqrtf}: enable the single-precision reciprocal square root approximation instructions; |
| @code{rsqrtd}: enable the double-precision reciprocal square root approximation instructions; |
| |
| So, for example, @option{-mrecip=all,!rsqrtd} enables |
| all of the reciprocal estimate instructions, except for the |
| @code{FRSQRTE}, @code{XSRSQRTEDP}, and @code{XVRSQRTEDP} instructions |
| which handle the double-precision reciprocal square root calculations. |
| |
| @item -mrecip-precision |
| @itemx -mno-recip-precision |
| @opindex mrecip-precision |
| Assume (do not assume) that the reciprocal estimate instructions |
| provide higher-precision estimates than is mandated by the PowerPC |
| ABI. Selecting @option{-mcpu=power6} or @option{-mcpu=power7} |
| automatically selects @option{-mrecip-precision}. The double-precision |
| square root estimate instructions are not generated by |
| default on low-precision machines, since they do not provide an |
| estimate that converges after three steps. |
| |
| @item -mveclibabi=@var{type} |
| @opindex mveclibabi |
| Specifies the ABI type to use for vectorizing intrinsics using an |
| external library. The only type supported at present is @code{mass}, |
| which specifies to use IBM's Mathematical Acceleration Subsystem |
| (MASS) libraries for vectorizing intrinsics using external libraries. |
| GCC currently emits calls to @code{acosd2}, @code{acosf4}, |
| @code{acoshd2}, @code{acoshf4}, @code{asind2}, @code{asinf4}, |
| @code{asinhd2}, @code{asinhf4}, @code{atan2d2}, @code{atan2f4}, |
| @code{atand2}, @code{atanf4}, @code{atanhd2}, @code{atanhf4}, |
| @code{cbrtd2}, @code{cbrtf4}, @code{cosd2}, @code{cosf4}, |
| @code{coshd2}, @code{coshf4}, @code{erfcd2}, @code{erfcf4}, |
| @code{erfd2}, @code{erff4}, @code{exp2d2}, @code{exp2f4}, |
| @code{expd2}, @code{expf4}, @code{expm1d2}, @code{expm1f4}, |
| @code{hypotd2}, @code{hypotf4}, @code{lgammad2}, @code{lgammaf4}, |
| @code{log10d2}, @code{log10f4}, @code{log1pd2}, @code{log1pf4}, |
| @code{log2d2}, @code{log2f4}, @code{logd2}, @code{logf4}, |
| @code{powd2}, @code{powf4}, @code{sind2}, @code{sinf4}, @code{sinhd2}, |
| @code{sinhf4}, @code{sqrtd2}, @code{sqrtf4}, @code{tand2}, |
| @code{tanf4}, @code{tanhd2}, and @code{tanhf4} when generating code |
| for power7. Both @option{-ftree-vectorize} and |
| @option{-funsafe-math-optimizations} must also be enabled. The MASS |
| libraries must be specified at link time. |
| |
| @item -mfriz |
| @itemx -mno-friz |
| @opindex mfriz |
| Generate (do not generate) the @code{friz} instruction when the |
| @option{-funsafe-math-optimizations} option is used to optimize |
| rounding of floating-point values to 64-bit integer and back to floating |
| point. The @code{friz} instruction does not return the same value if |
| the floating-point number is too large to fit in an integer. |
| |
| @item -mpointers-to-nested-functions |
| @itemx -mno-pointers-to-nested-functions |
| @opindex mpointers-to-nested-functions |
| Generate (do not generate) code to load up the static chain register |
| (@var{r11}) when calling through a pointer on AIX and 64-bit Linux |
| systems where a function pointer points to a 3-word descriptor giving |
| the function address, TOC value to be loaded in register @var{r2}, and |
| static chain value to be loaded in register @var{r11}. The |
| @option{-mpointers-to-nested-functions} is on by default. You cannot |
| call through pointers to nested functions or pointers |
| to functions compiled in other languages that use the static chain if |
| you use the @option{-mno-pointers-to-nested-functions}. |
| |
| @item -msave-toc-indirect |
| @itemx -mno-save-toc-indirect |
| @opindex msave-toc-indirect |
| Generate (do not generate) code to save the TOC value in the reserved |
| stack location in the function prologue if the function calls through |
| a pointer on AIX and 64-bit Linux systems. If the TOC value is not |
| saved in the prologue, it is saved just before the call through the |
| pointer. The @option{-mno-save-toc-indirect} option is the default. |
| @end table |
| |
| @node RX Options |
| @subsection RX Options |
| @cindex RX Options |
| |
| These command-line options are defined for RX targets: |
| |
| @table @gcctabopt |
| @item -m64bit-doubles |
| @itemx -m32bit-doubles |
| @opindex m64bit-doubles |
| @opindex m32bit-doubles |
| Make the @code{double} data type be 64 bits (@option{-m64bit-doubles}) |
| or 32 bits (@option{-m32bit-doubles}) in size. The default is |
| @option{-m32bit-doubles}. @emph{Note} RX floating-point hardware only |
| works on 32-bit values, which is why the default is |
| @option{-m32bit-doubles}. |
| |
| @item -fpu |
| @itemx -nofpu |
| @opindex fpu |
| @opindex nofpu |
| Enables (@option{-fpu}) or disables (@option{-nofpu}) the use of RX |
| floating-point hardware. The default is enabled for the @var{RX600} |
| series and disabled for the @var{RX200} series. |
| |
| Floating-point instructions are only generated for 32-bit floating-point |
| values, however, so the FPU hardware is not used for doubles if the |
| @option{-m64bit-doubles} option is used. |
| |
| @emph{Note} If the @option{-fpu} option is enabled then |
| @option{-funsafe-math-optimizations} is also enabled automatically. |
| This is because the RX FPU instructions are themselves unsafe. |
| |
| @item -mcpu=@var{name} |
| @opindex -mcpu |
| Selects the type of RX CPU to be targeted. Currently three types are |
| supported, the generic @var{RX600} and @var{RX200} series hardware and |
| the specific @var{RX610} CPU. The default is @var{RX600}. |
| |
| The only difference between @var{RX600} and @var{RX610} is that the |
| @var{RX610} does not support the @code{MVTIPL} instruction. |
| |
| The @var{RX200} series does not have a hardware floating-point unit |
| and so @option{-nofpu} is enabled by default when this type is |
| selected. |
| |
| @item -mbig-endian-data |
| @itemx -mlittle-endian-data |
| @opindex mbig-endian-data |
| @opindex mlittle-endian-data |
| Store data (but not code) in the big-endian format. The default is |
| @option{-mlittle-endian-data}, i.e.@: to store data in the little-endian |
| format. |
| |
| @item -msmall-data-limit=@var{N} |
| @opindex msmall-data-limit |
| Specifies the maximum size in bytes of global and static variables |
| which can be placed into the small data area. Using the small data |
| area can lead to smaller and faster code, but the size of area is |
| limited and it is up to the programmer to ensure that the area does |
| not overflow. Also when the small data area is used one of the RX's |
| registers (usually @code{r13}) is reserved for use pointing to this |
| area, so it is no longer available for use by the compiler. This |
| could result in slower and/or larger code if variables are pushed onto |
| the stack instead of being held in this register. |
| |
| Note, common variables (variables that have not been initialized) and |
| constants are not placed into the small data area as they are assigned |
| to other sections in the output executable. |
| |
| The default value is zero, which disables this feature. Note, this |
| feature is not enabled by default with higher optimization levels |
| (@option{-O2} etc) because of the potentially detrimental effects of |
| reserving a register. It is up to the programmer to experiment and |
| discover whether this feature is of benefit to their program. See the |
| description of the @option{-mpid} option for a description of how the |
| actual register to hold the small data area pointer is chosen. |
| |
| @item -msim |
| @itemx -mno-sim |
| @opindex msim |
| @opindex mno-sim |
| Use the simulator runtime. The default is to use the libgloss |
| board-specific runtime. |
| |
| @item -mas100-syntax |
| @itemx -mno-as100-syntax |
| @opindex mas100-syntax |
| @opindex mno-as100-syntax |
| When generating assembler output use a syntax that is compatible with |
| Renesas's AS100 assembler. This syntax can also be handled by the GAS |
| assembler, but it has some restrictions so it is not generated by default. |
| |
| @item -mmax-constant-size=@var{N} |
| @opindex mmax-constant-size |
| Specifies the maximum size, in bytes, of a constant that can be used as |
| an operand in a RX instruction. Although the RX instruction set does |
| allow constants of up to 4 bytes in length to be used in instructions, |
| a longer value equates to a longer instruction. Thus in some |
| circumstances it can be beneficial to restrict the size of constants |
| that are used in instructions. Constants that are too big are instead |
| placed into a constant pool and referenced via register indirection. |
| |
| The value @var{N} can be between 0 and 4. A value of 0 (the default) |
| or 4 means that constants of any size are allowed. |
| |
| @item -mrelax |
| @opindex mrelax |
| Enable linker relaxation. Linker relaxation is a process whereby the |
| linker attempts to reduce the size of a program by finding shorter |
| versions of various instructions. Disabled by default. |
| |
| @item -mint-register=@var{N} |
| @opindex mint-register |
| Specify the number of registers to reserve for fast interrupt handler |
| functions. The value @var{N} can be between 0 and 4. A value of 1 |
| means that register @code{r13} is reserved for the exclusive use |
| of fast interrupt handlers. A value of 2 reserves @code{r13} and |
| @code{r12}. A value of 3 reserves @code{r13}, @code{r12} and |
| @code{r11}, and a value of 4 reserves @code{r13} through @code{r10}. |
| A value of 0, the default, does not reserve any registers. |
| |
| @item -msave-acc-in-interrupts |
| @opindex msave-acc-in-interrupts |
| Specifies that interrupt handler functions should preserve the |
| accumulator register. This is only necessary if normal code might use |
| the accumulator register, for example because it performs 64-bit |
| multiplications. The default is to ignore the accumulator as this |
| makes the interrupt handlers faster. |
| |
| @item -mpid |
| @itemx -mno-pid |
| @opindex mpid |
| @opindex mno-pid |
| Enables the generation of position independent data. When enabled any |
| access to constant data is done via an offset from a base address |
| held in a register. This allows the location of constant data to be |
| determined at run time without requiring the executable to be |
| relocated, which is a benefit to embedded applications with tight |
| memory constraints. Data that can be modified is not affected by this |
| option. |
| |
| Note, using this feature reserves a register, usually @code{r13}, for |
| the constant data base address. This can result in slower and/or |
| larger code, especially in complicated functions. |
| |
| The actual register chosen to hold the constant data base address |
| depends upon whether the @option{-msmall-data-limit} and/or the |
| @option{-mint-register} command-line options are enabled. Starting |
| with register @code{r13} and proceeding downwards, registers are |
| allocated first to satisfy the requirements of @option{-mint-register}, |
| then @option{-mpid} and finally @option{-msmall-data-limit}. Thus it |
| is possible for the small data area register to be @code{r8} if both |
| @option{-mint-register=4} and @option{-mpid} are specified on the |
| command line. |
| |
| By default this feature is not enabled. The default can be restored |
| via the @option{-mno-pid} command-line option. |
| |
| @end table |
| |
| @emph{Note:} The generic GCC command-line option @option{-ffixed-@var{reg}} |
| has special significance to the RX port when used with the |
| @code{interrupt} function attribute. This attribute indicates a |
| function intended to process fast interrupts. GCC ensures |
| that it only uses the registers @code{r10}, @code{r11}, @code{r12} |
| and/or @code{r13} and only provided that the normal use of the |
| corresponding registers have been restricted via the |
| @option{-ffixed-@var{reg}} or @option{-mint-register} command-line |
| options. |
| |
| @node S/390 and zSeries Options |
| @subsection S/390 and zSeries Options |
| @cindex S/390 and zSeries Options |
| |
| These are the @samp{-m} options defined for the S/390 and zSeries architecture. |
| |
| @table @gcctabopt |
| @item -mhard-float |
| @itemx -msoft-float |
| @opindex mhard-float |
| @opindex msoft-float |
| Use (do not use) the hardware floating-point instructions and registers |
| for floating-point operations. When @option{-msoft-float} is specified, |
| functions in @file{libgcc.a} are used to perform floating-point |
| operations. When @option{-mhard-float} is specified, the compiler |
| generates IEEE floating-point instructions. This is the default. |
| |
| @item -mhard-dfp |
| @itemx -mno-hard-dfp |
| @opindex mhard-dfp |
| @opindex mno-hard-dfp |
| Use (do not use) the hardware decimal-floating-point instructions for |
| decimal-floating-point operations. When @option{-mno-hard-dfp} is |
| specified, functions in @file{libgcc.a} are used to perform |
| decimal-floating-point operations. When @option{-mhard-dfp} is |
| specified, the compiler generates decimal-floating-point hardware |
| instructions. This is the default for @option{-march=z9-ec} or higher. |
| |
| @item -mlong-double-64 |
| @itemx -mlong-double-128 |
| @opindex mlong-double-64 |
| @opindex mlong-double-128 |
| These switches control the size of @code{long double} type. A size |
| of 64 bits makes the @code{long double} type equivalent to the @code{double} |
| type. This is the default. |
| |
| @item -mbackchain |
| @itemx -mno-backchain |
| @opindex mbackchain |
| @opindex mno-backchain |
| Store (do not store) the address of the caller's frame as backchain pointer |
| into the callee's stack frame. |
| A backchain may be needed to allow debugging using tools that do not understand |
| DWARF 2 call frame information. |
| When @option{-mno-packed-stack} is in effect, the backchain pointer is stored |
| at the bottom of the stack frame; when @option{-mpacked-stack} is in effect, |
| the backchain is placed into the topmost word of the 96/160 byte register |
| save area. |
| |
| In general, code compiled with @option{-mbackchain} is call-compatible with |
| code compiled with @option{-mmo-backchain}; however, use of the backchain |
| for debugging purposes usually requires that the whole binary is built with |
| @option{-mbackchain}. Note that the combination of @option{-mbackchain}, |
| @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order |
| to build a linux kernel use @option{-msoft-float}. |
| |
| The default is to not maintain the backchain. |
| |
| @item -mpacked-stack |
| @itemx -mno-packed-stack |
| @opindex mpacked-stack |
| @opindex mno-packed-stack |
| Use (do not use) the packed stack layout. When @option{-mno-packed-stack} is |
| specified, the compiler uses the all fields of the 96/160 byte register save |
| area only for their default purpose; unused fields still take up stack space. |
| When @option{-mpacked-stack} is specified, register save slots are densely |
| packed at the top of the register save area; unused space is reused for other |
| purposes, allowing for more efficient use of the available stack space. |
| However, when @option{-mbackchain} is also in effect, the topmost word of |
| the save area is always used to store the backchain, and the return address |
| register is always saved two words below the backchain. |
| |
| As long as the stack frame backchain is not used, code generated with |
| @option{-mpacked-stack} is call-compatible with code generated with |
| @option{-mno-packed-stack}. Note that some non-FSF releases of GCC 2.95 for |
| S/390 or zSeries generated code that uses the stack frame backchain at run |
| time, not just for debugging purposes. Such code is not call-compatible |
| with code compiled with @option{-mpacked-stack}. Also, note that the |
| combination of @option{-mbackchain}, |
| @option{-mpacked-stack} and @option{-mhard-float} is not supported. In order |
| to build a linux kernel use @option{-msoft-float}. |
| |
| The default is to not use the packed stack layout. |
| |
| @item -msmall-exec |
| @itemx -mno-small-exec |
| @opindex msmall-exec |
| @opindex mno-small-exec |
| Generate (or do not generate) code using the @code{bras} instruction |
| to do subroutine calls. |
| This only works reliably if the total executable size does not |
| exceed 64k. The default is to use the @code{basr} instruction instead, |
| which does not have this limitation. |
| |
| @item -m64 |
| @itemx -m31 |
| @opindex m64 |
| @opindex m31 |
| When @option{-m31} is specified, generate code compliant to the |
| GNU/Linux for S/390 ABI@. When @option{-m64} is specified, generate |
| code compliant to the GNU/Linux for zSeries ABI@. This allows GCC in |
| particular to generate 64-bit instructions. For the @samp{s390} |
| targets, the default is @option{-m31}, while the @samp{s390x} |
| targets default to @option{-m64}. |
| |
| @item -mzarch |
| @itemx -mesa |
| @opindex mzarch |
| @opindex mesa |
| When @option{-mzarch} is specified, generate code using the |
| instructions available on z/Architecture. |
| When @option{-mesa} is specified, generate code using the |
| instructions available on ESA/390. Note that @option{-mesa} is |
| not possible with @option{-m64}. |
| When generating code compliant to the GNU/Linux for S/390 ABI, |
| the default is @option{-mesa}. When generating code compliant |
| to the GNU/Linux for zSeries ABI, the default is @option{-mzarch}. |
| |
| @item -mmvcle |
| @itemx -mno-mvcle |
| @opindex mmvcle |
| @opindex mno-mvcle |
| Generate (or do not generate) code using the @code{mvcle} instruction |
| to perform block moves. When @option{-mno-mvcle} is specified, |
| use a @code{mvc} loop instead. This is the default unless optimizing for |
| size. |
| |
| @item -mdebug |
| @itemx -mno-debug |
| @opindex mdebug |
| @opindex mno-debug |
| Print (or do not print) additional debug information when compiling. |
| The default is to not print debug information. |
| |
| @item -march=@var{cpu-type} |
| @opindex march |
| Generate code that runs on @var{cpu-type}, which is the name of a system |
| representing a certain processor type. Possible values for |
| @var{cpu-type} are @samp{g5}, @samp{g6}, @samp{z900}, @samp{z990}, |
| @samp{z9-109}, @samp{z9-ec} and @samp{z10}. |
| When generating code using the instructions available on z/Architecture, |
| the default is @option{-march=z900}. Otherwise, the default is |
| @option{-march=g5}. |
| |
| @item -mtune=@var{cpu-type} |
| @opindex mtune |
| Tune to @var{cpu-type} everything applicable about the generated code, |
| except for the ABI and the set of available instructions. |
| The list of @var{cpu-type} values is the same as for @option{-march}. |
| The default is the value used for @option{-march}. |
| |
| @item -mtpf-trace |
| @itemx -mno-tpf-trace |
| @opindex mtpf-trace |
| @opindex mno-tpf-trace |
| Generate code that adds (does not add) in TPF OS specific branches to trace |
| routines in the operating system. This option is off by default, even |
| when compiling for the TPF OS@. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Generate code that uses (does not use) the floating-point multiply and |
| accumulate instructions. These instructions are generated by default if |
| hardware floating point is used. |
| |
| @item -mwarn-framesize=@var{framesize} |
| @opindex mwarn-framesize |
| Emit a warning if the current function exceeds the given frame size. Because |
| this is a compile-time check it doesn't need to be a real problem when the program |
| runs. It is intended to identify functions that most probably cause |
| a stack overflow. It is useful to be used in an environment with limited stack |
| size e.g.@: the linux kernel. |
| |
| @item -mwarn-dynamicstack |
| @opindex mwarn-dynamicstack |
| Emit a warning if the function calls @code{alloca} or uses dynamically-sized |
| arrays. This is generally a bad idea with a limited stack size. |
| |
| @item -mstack-guard=@var{stack-guard} |
| @itemx -mstack-size=@var{stack-size} |
| @opindex mstack-guard |
| @opindex mstack-size |
| If these options are provided the S/390 back end emits additional instructions in |
| the function prologue that trigger a trap if the stack size is @var{stack-guard} |
| bytes above the @var{stack-size} (remember that the stack on S/390 grows downward). |
| If the @var{stack-guard} option is omitted the smallest power of 2 larger than |
| the frame size of the compiled function is chosen. |
| These options are intended to be used to help debugging stack overflow problems. |
| The additionally emitted code causes only little overhead and hence can also be |
| used in production-like systems without greater performance degradation. The given |
| values have to be exact powers of 2 and @var{stack-size} has to be greater than |
| @var{stack-guard} without exceeding 64k. |
| In order to be efficient the extra code makes the assumption that the stack starts |
| at an address aligned to the value given by @var{stack-size}. |
| The @var{stack-guard} option can only be used in conjunction with @var{stack-size}. |
| @end table |
| |
| @node Score Options |
| @subsection Score Options |
| @cindex Score Options |
| |
| These options are defined for Score implementations: |
| |
| @table @gcctabopt |
| @item -meb |
| @opindex meb |
| Compile code for big-endian mode. This is the default. |
| |
| @item -mel |
| @opindex mel |
| Compile code for little-endian mode. |
| |
| @item -mnhwloop |
| @opindex mnhwloop |
| Disable generation of @code{bcnz} instructions. |
| |
| @item -muls |
| @opindex muls |
| Enable generation of unaligned load and store instructions. |
| |
| @item -mmac |
| @opindex mmac |
| Enable the use of multiply-accumulate instructions. Disabled by default. |
| |
| @item -mscore5 |
| @opindex mscore5 |
| Specify the SCORE5 as the target architecture. |
| |
| @item -mscore5u |
| @opindex mscore5u |
| Specify the SCORE5U of the target architecture. |
| |
| @item -mscore7 |
| @opindex mscore7 |
| Specify the SCORE7 as the target architecture. This is the default. |
| |
| @item -mscore7d |
| @opindex mscore7d |
| Specify the SCORE7D as the target architecture. |
| @end table |
| |
| @node SH Options |
| @subsection SH Options |
| |
| These @samp{-m} options are defined for the SH implementations: |
| |
| @table @gcctabopt |
| @item -m1 |
| @opindex m1 |
| Generate code for the SH1. |
| |
| @item -m2 |
| @opindex m2 |
| Generate code for the SH2. |
| |
| @item -m2e |
| Generate code for the SH2e. |
| |
| @item -m2a-nofpu |
| @opindex m2a-nofpu |
| Generate code for the SH2a without FPU, or for a SH2a-FPU in such a way |
| that the floating-point unit is not used. |
| |
| @item -m2a-single-only |
| @opindex m2a-single-only |
| Generate code for the SH2a-FPU, in such a way that no double-precision |
| floating-point operations are used. |
| |
| @item -m2a-single |
| @opindex m2a-single |
| Generate code for the SH2a-FPU assuming the floating-point unit is in |
| single-precision mode by default. |
| |
| @item -m2a |
| @opindex m2a |
| Generate code for the SH2a-FPU assuming the floating-point unit is in |
| double-precision mode by default. |
| |
| @item -m3 |
| @opindex m3 |
| Generate code for the SH3. |
| |
| @item -m3e |
| @opindex m3e |
| Generate code for the SH3e. |
| |
| @item -m4-nofpu |
| @opindex m4-nofpu |
| Generate code for the SH4 without a floating-point unit. |
| |
| @item -m4-single-only |
| @opindex m4-single-only |
| Generate code for the SH4 with a floating-point unit that only |
| supports single-precision arithmetic. |
| |
| @item -m4-single |
| @opindex m4-single |
| Generate code for the SH4 assuming the floating-point unit is in |
| single-precision mode by default. |
| |
| @item -m4 |
| @opindex m4 |
| Generate code for the SH4. |
| |
| @item -m4a-nofpu |
| @opindex m4a-nofpu |
| Generate code for the SH4al-dsp, or for a SH4a in such a way that the |
| floating-point unit is not used. |
| |
| @item -m4a-single-only |
| @opindex m4a-single-only |
| Generate code for the SH4a, in such a way that no double-precision |
| floating-point operations are used. |
| |
| @item -m4a-single |
| @opindex m4a-single |
| Generate code for the SH4a assuming the floating-point unit is in |
| single-precision mode by default. |
| |
| @item -m4a |
| @opindex m4a |
| Generate code for the SH4a. |
| |
| @item -m4al |
| @opindex m4al |
| Same as @option{-m4a-nofpu}, except that it implicitly passes |
| @option{-dsp} to the assembler. GCC doesn't generate any DSP |
| instructions at the moment. |
| |
| @item -mb |
| @opindex mb |
| Compile code for the processor in big-endian mode. |
| |
| @item -ml |
| @opindex ml |
| Compile code for the processor in little-endian mode. |
| |
| @item -mdalign |
| @opindex mdalign |
| Align doubles at 64-bit boundaries. Note that this changes the calling |
| conventions, and thus some functions from the standard C library do |
| not work unless you recompile it first with @option{-mdalign}. |
| |
| @item -mrelax |
| @opindex mrelax |
| Shorten some address references at link time, when possible; uses the |
| linker option @option{-relax}. |
| |
| @item -mbigtable |
| @opindex mbigtable |
| Use 32-bit offsets in @code{switch} tables. The default is to use |
| 16-bit offsets. |
| |
| @item -mbitops |
| @opindex mbitops |
| Enable the use of bit manipulation instructions on SH2A. |
| |
| @item -mfmovd |
| @opindex mfmovd |
| Enable the use of the instruction @code{fmovd}. Check @option{-mdalign} for |
| alignment constraints. |
| |
| @item -mhitachi |
| @opindex mhitachi |
| Comply with the calling conventions defined by Renesas. |
| |
| @item -mrenesas |
| @opindex mhitachi |
| Comply with the calling conventions defined by Renesas. |
| |
| @item -mno-renesas |
| @opindex mhitachi |
| Comply with the calling conventions defined for GCC before the Renesas |
| conventions were available. This option is the default for all |
| targets of the SH toolchain. |
| |
| @item -mnomacsave |
| @opindex mnomacsave |
| Mark the @code{MAC} register as call-clobbered, even if |
| @option{-mhitachi} is given. |
| |
| @item -mieee |
| @item -mno-ieee |
| @opindex mieee |
| @opindex mnoieee |
| Control the IEEE compliance of floating-point comparisons, which affects the |
| handling of cases where the result of a comparison is unordered. By default |
| @option{-mieee} is implicitly enabled. If @option{-ffinite-math-only} is |
| enabled @option{-mno-ieee} is implicitly set, which results in faster |
| floating-point greater-equal and less-equal comparisons. The implcit settings |
| can be overridden by specifying either @option{-mieee} or @option{-mno-ieee}. |
| |
| @item -minline-ic_invalidate |
| @opindex minline-ic_invalidate |
| Inline code to invalidate instruction cache entries after setting up |
| nested function trampolines. |
| This option has no effect if @option{-musermode} is in effect and the selected |
| code generation option (e.g. @option{-m4}) does not allow the use of the @code{icbi} |
| instruction. |
| If the selected code generation option does not allow the use of the @code{icbi} |
| instruction, and @option{-musermode} is not in effect, the inlined code |
| manipulates the instruction cache address array directly with an associative |
| write. This not only requires privileged mode at run time, but it also |
| fails if the cache line had been mapped via the TLB and has become unmapped. |
| |
| @item -misize |
| @opindex misize |
| Dump instruction size and location in the assembly code. |
| |
| @item -mpadstruct |
| @opindex mpadstruct |
| This option is deprecated. It pads structures to multiple of 4 bytes, |
| which is incompatible with the SH ABI@. |
| |
| @item -msoft-atomic |
| @opindex msoft-atomic |
| Generate GNU/Linux compatible gUSA software atomic sequences for the atomic |
| built-in functions. The generated atomic sequences require support from the |
| interrupt / exception handling code of the system and are only suitable for |
| single-core systems. They will not operate correctly on multi-core systems. |
| This option is enabled by default when the target is @code{sh-*-linux*}. |
| When the target is SH4A, this option will also partially utilize the hardware |
| atomic instructions @code{movli.l} and @code{movco.l} to create more |
| efficient code. |
| For details on the atomic built-in functions see @ref{__atomic Builtins}. |
| |
| @item -mhard-atomic |
| @opindex hard-atomic |
| Generate hardware atomic sequences for the atomic built-in functions. This |
| is only available on SH4A and is suitable for multi-core systems. Code |
| compiled with this option will also be compatible with gUSA aware |
| interrupt / exception handling systems. In contrast to the |
| @option{-msoft-atomic} option this will only use the instructions |
| @code{movli.l} and @code{movco.l} to create atomic sequences. |
| |
| @item -mtas |
| @opindex mtas |
| Generate the @code{tas.b} opcode for @code{__atomic_test_and_set}. |
| Notice that depending on the particular hardware and software configuration |
| this can degrade overall performance due to the operand cache line flushes |
| that are implied by the @code{tas.b} instruction. On multi-core SH4A |
| processors the @code{tas.b} instruction must be used with caution since it |
| can result in data corruption for certain cache configurations. |
| |
| @item -mspace |
| @opindex mspace |
| Optimize for space instead of speed. Implied by @option{-Os}. |
| |
| @item -mprefergot |
| @opindex mprefergot |
| When generating position-independent code, emit function calls using |
| the Global Offset Table instead of the Procedure Linkage Table. |
| |
| @item -musermode |
| @opindex musermode |
| Don't generate privileged mode only code. This option |
| implies @option{-mno-inline-ic_invalidate} |
| if the inlined code would not work in user mode. |
| This is the default when the target is @code{sh-*-linux*}. |
| |
| @item -multcost=@var{number} |
| @opindex multcost=@var{number} |
| Set the cost to assume for a multiply insn. |
| |
| @item -mdiv=@var{strategy} |
| @opindex mdiv=@var{strategy} |
| Set the division strategy to use for SHmedia code. @var{strategy} must be |
| one of: |
| |
| @table @samp |
| |
| @item fp |
| Performs the operation in floating point. This has a very high latency, |
| but needs only a few instructions, so it might be a good choice if |
| your code has enough easily-exploitable ILP to allow the compiler to |
| schedule the floating-point instructions together with other instructions. |
| Division by zero causes a floating-point exception. |
| |
| @item inv |
| Uses integer operations to calculate the inverse of the divisor, |
| and then multiplies the dividend with the inverse. This strategy allows |
| CSE and hoisting of the inverse calculation. Division by zero calculates |
| an unspecified result, but does not trap. |
| |
| @item inv:minlat |
| A variant of @samp{inv} where, if no CSE or hoisting opportunities |
| have been found, or if the entire operation has been hoisted to the same |
| place, the last stages of the inverse calculation are intertwined with the |
| final multiply to reduce the overall latency, at the expense of using a few |
| more instructions, and thus offering fewer scheduling opportunities with |
| other code. |
| |
| @item call |
| Calls a library function that usually implements the @samp{inv:minlat} |
| strategy. |
| This gives high code density for @code{m5-*media-nofpu} compilations. |
| |
| @item call2 |
| Uses a different entry point of the same library function, where it |
| assumes that a pointer to a lookup table has already been set up, which |
| exposes the pointer load to CSE and code hoisting optimizations. |
| |
| @item inv:call |
| @itemx inv:call2 |
| @itemx inv:fp |
| Use the @samp{inv} algorithm for initial |
| code generation, but if the code stays unoptimized, revert to the @samp{call}, |
| @samp{call2}, or @samp{fp} strategies, respectively. Note that the |
| potentially-trapping side effect of division by zero is carried by a |
| separate instruction, so it is possible that all the integer instructions |
| are hoisted out, but the marker for the side effect stays where it is. |
| A recombination to floating-point operations or a call is not possible |
| in that case. |
| |
| @item inv20u |
| @itemx inv20l |
| Variants of the @samp{inv:minlat} strategy. In the case |
| that the inverse calculation is not separated from the multiply, they speed |
| up division where the dividend fits into 20 bits (plus sign where applicable) |
| by inserting a test to skip a number of operations in this case; this test |
| slows down the case of larger dividends. @samp{inv20u} assumes the case of a such |
| a small dividend to be unlikely, and @samp{inv20l} assumes it to be likely. |
| |
| @end table |
| |
| @item -maccumulate-outgoing-args |
| @opindex maccumulate-outgoing-args |
| Reserve space once for outgoing arguments in the function prologue rather |
| than around each call. Generally beneficial for performance and size. Also |
| needed for unwinding to avoid changing the stack frame around conditional code. |
| |
| @item -mdivsi3_libfunc=@var{name} |
| @opindex mdivsi3_libfunc=@var{name} |
| Set the name of the library function used for 32-bit signed division to |
| @var{name}. |
| This only affects the name used in the @samp{call} and @samp{inv:call} |
| division strategies, and the compiler still expects the same |
| sets of input/output/clobbered registers as if this option were not present. |
| |
| @item -mfixed-range=@var{register-range} |
| @opindex mfixed-range |
| Generate code treating the given register range as fixed registers. |
| A fixed register is one that the register allocator can not use. This is |
| useful when compiling kernel code. A register range is specified as |
| two registers separated by a dash. Multiple register ranges can be |
| specified separated by a comma. |
| |
| @item -mindexed-addressing |
| @opindex mindexed-addressing |
| Enable the use of the indexed addressing mode for SHmedia32/SHcompact. |
| This is only safe if the hardware and/or OS implement 32-bit wrap-around |
| semantics for the indexed addressing mode. The architecture allows the |
| implementation of processors with 64-bit MMU, which the OS could use to |
| get 32-bit addressing, but since no current hardware implementation supports |
| this or any other way to make the indexed addressing mode safe to use in |
| the 32-bit ABI, the default is @option{-mno-indexed-addressing}. |
| |
| @item -mgettrcost=@var{number} |
| @opindex mgettrcost=@var{number} |
| Set the cost assumed for the @code{gettr} instruction to @var{number}. |
| The default is 2 if @option{-mpt-fixed} is in effect, 100 otherwise. |
| |
| @item -mpt-fixed |
| @opindex mpt-fixed |
| Assume @code{pt*} instructions won't trap. This generally generates |
| better-scheduled code, but is unsafe on current hardware. |
| The current architecture |
| definition says that @code{ptabs} and @code{ptrel} trap when the target |
| anded with 3 is 3. |
| This has the unintentional effect of making it unsafe to schedule these |
| instructions before a branch, or hoist them out of a loop. For example, |
| @code{__do_global_ctors}, a part of @file{libgcc} |
| that runs constructors at program |
| startup, calls functions in a list which is delimited by @minus{}1. With the |
| @option{-mpt-fixed} option, the @code{ptabs} is done before testing against @minus{}1. |
| That means that all the constructors run a bit more quickly, but when |
| the loop comes to the end of the list, the program crashes because @code{ptabs} |
| loads @minus{}1 into a target register. |
| |
| Since this option is unsafe for any |
| hardware implementing the current architecture specification, the default |
| is @option{-mno-pt-fixed}. Unless specified explicitly with |
| @option{-mgettrcost}, @option{-mno-pt-fixed} also implies @option{-mgettrcost=100}; |
| this deters register allocation from using target registers for storing |
| ordinary integers. |
| |
| @item -minvalid-symbols |
| @opindex minvalid-symbols |
| Assume symbols might be invalid. Ordinary function symbols generated by |
| the compiler are always valid to load with |
| @code{movi}/@code{shori}/@code{ptabs} or |
| @code{movi}/@code{shori}/@code{ptrel}, |
| but with assembler and/or linker tricks it is possible |
| to generate symbols that cause @code{ptabs} or @code{ptrel} to trap. |
| This option is only meaningful when @option{-mno-pt-fixed} is in effect. |
| It prevents cross-basic-block CSE, hoisting and most scheduling |
| of symbol loads. The default is @option{-mno-invalid-symbols}. |
| |
| @item -mbranch-cost=@var{num} |
| @opindex mbranch-cost=@var{num} |
| Assume @var{num} to be the cost for a branch instruction. Higher numbers |
| make the compiler try to generate more branch-free code if possible. |
| If not specified the value is selected depending on the processor type that |
| is being compiled for. |
| |
| @item -mzdcbranch |
| @itemx -mno-zdcbranch |
| @opindex mzdcbranch |
| @opindex mno-zdcbranch |
| Assume (do not assume) that zero displacement conditional branch instructions |
| @code{bt} and @code{bf} are fast. If @option{-mzdcbranch} is specified, the |
| compiler will try to prefer zero displacement branch code sequences. This is |
| enabled by default when generating code for SH4 and SH4A. It can be explicitly |
| disabled by specifying @option{-mno-zdcbranch}. |
| |
| @item -mcbranchdi |
| @opindex mcbranchdi |
| Enable the @code{cbranchdi4} instruction pattern. |
| |
| @item -mcmpeqdi |
| @opindex mcmpeqdi |
| Emit the @code{cmpeqdi_t} instruction pattern even when @option{-mcbranchdi} |
| is in effect. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Generate code that uses (does not use) the floating-point multiply and |
| accumulate instructions. These instructions are generated by default |
| if hardware floating point is used. The machine-dependent |
| @option{-mfused-madd} option is now mapped to the machine-independent |
| @option{-ffp-contract=fast} option, and @option{-mno-fused-madd} is |
| mapped to @option{-ffp-contract=off}. |
| |
| @item -mfsca |
| @itemx -mno-fsca |
| @opindex mfsca |
| @opindex mno-fsca |
| Allow or disallow the compiler to emit the @code{fsca} instruction for sine |
| and cosine approximations. The option @code{-mfsca} must be used in |
| combination with @code{-funsafe-math-optimizations}. It is enabled by default |
| when generating code for SH4A. Using @code{-mno-fsca} disables sine and cosine |
| approximations even if @code{-funsafe-math-optimizations} is in effect. |
| |
| @item -mfsrra |
| @itemx -mno-fsrra |
| @opindex mfsrra |
| @opindex mno-fsrra |
| Allow or disallow the compiler to emit the @code{fsrra} instruction for |
| reciprocal square root approximations. The option @code{-mfsrra} must be used |
| in combination with @code{-funsafe-math-optimizations} and |
| @code{-ffinite-math-only}. It is enabled by default when generating code for |
| SH4A. Using @code{-mno-fsrra} disables reciprocal square root approximations |
| even if @code{-funsafe-math-optimizations} and @code{-ffinite-math-only} are |
| in effect. |
| |
| @item -mpretend-cmove |
| @opindex mpretend-cmove |
| Prefer zero-displacement conditional branches for conditional move instruction |
| patterns. This can result in faster code on the SH4 processor. |
| |
| @end table |
| |
| @node Solaris 2 Options |
| @subsection Solaris 2 Options |
| @cindex Solaris 2 options |
| |
| These @samp{-m} options are supported on Solaris 2: |
| |
| @table @gcctabopt |
| @item -mimpure-text |
| @opindex mimpure-text |
| @option{-mimpure-text}, used in addition to @option{-shared}, tells |
| the compiler to not pass @option{-z text} to the linker when linking a |
| shared object. Using this option, you can link position-dependent |
| code into a shared object. |
| |
| @option{-mimpure-text} suppresses the ``relocations remain against |
| allocatable but non-writable sections'' linker error message. |
| However, the necessary relocations trigger copy-on-write, and the |
| shared object is not actually shared across processes. Instead of |
| using @option{-mimpure-text}, you should compile all source code with |
| @option{-fpic} or @option{-fPIC}. |
| |
| @end table |
| |
| These switches are supported in addition to the above on Solaris 2: |
| |
| @table @gcctabopt |
| @item -pthreads |
| @opindex pthreads |
| Add support for multithreading using the POSIX threads library. This |
| option sets flags for both the preprocessor and linker. This option does |
| not affect the thread safety of object code produced by the compiler or |
| that of libraries supplied with it. |
| |
| @item -pthread |
| @opindex pthread |
| This is a synonym for @option{-pthreads}. |
| @end table |
| |
| @node SPARC Options |
| @subsection SPARC Options |
| @cindex SPARC options |
| |
| These @samp{-m} options are supported on the SPARC: |
| |
| @table @gcctabopt |
| @item -mno-app-regs |
| @itemx -mapp-regs |
| @opindex mno-app-regs |
| @opindex mapp-regs |
| Specify @option{-mapp-regs} to generate output using the global registers |
| 2 through 4, which the SPARC SVR4 ABI reserves for applications. This |
| is the default. |
| |
| To be fully SVR4 ABI-compliant at the cost of some performance loss, |
| specify @option{-mno-app-regs}. You should compile libraries and system |
| software with this option. |
| |
| @item -mflat |
| @itemx -mno-flat |
| @opindex mflat |
| @opindex mno-flat |
| With @option{-mflat}, the compiler does not generate save/restore instructions |
| and uses a ``flat'' or single register window model. This model is compatible |
| with the regular register window model. The local registers and the input |
| registers (0--5) are still treated as ``call-saved'' registers and are |
| saved on the stack as needed. |
| |
| With @option{-mno-flat} (the default), the compiler generates save/restore |
| instructions (except for leaf functions). This is the normal operating mode. |
| |
| @item -mfpu |
| @itemx -mhard-float |
| @opindex mfpu |
| @opindex mhard-float |
| Generate output containing floating-point instructions. This is the |
| default. |
| |
| @item -mno-fpu |
| @itemx -msoft-float |
| @opindex mno-fpu |
| @opindex msoft-float |
| Generate output containing library calls for floating point. |
| @strong{Warning:} the requisite libraries are not available for all SPARC |
| targets. Normally the facilities of the machine's usual C compiler are |
| used, but this cannot be done directly in cross-compilation. You must make |
| your own arrangements to provide suitable library functions for |
| cross-compilation. The embedded targets @samp{sparc-*-aout} and |
| @samp{sparclite-*-*} do provide software floating-point support. |
| |
| @option{-msoft-float} changes the calling convention in the output file; |
| therefore, it is only useful if you compile @emph{all} of a program with |
| this option. In particular, you need to compile @file{libgcc.a}, the |
| library that comes with GCC, with @option{-msoft-float} in order for |
| this to work. |
| |
| @item -mhard-quad-float |
| @opindex mhard-quad-float |
| Generate output containing quad-word (long double) floating-point |
| instructions. |
| |
| @item -msoft-quad-float |
| @opindex msoft-quad-float |
| Generate output containing library calls for quad-word (long double) |
| floating-point instructions. The functions called are those specified |
| in the SPARC ABI@. This is the default. |
| |
| As of this writing, there are no SPARC implementations that have hardware |
| support for the quad-word floating-point instructions. They all invoke |
| a trap handler for one of these instructions, and then the trap handler |
| emulates the effect of the instruction. Because of the trap handler overhead, |
| this is much slower than calling the ABI library routines. Thus the |
| @option{-msoft-quad-float} option is the default. |
| |
| @item -mno-unaligned-doubles |
| @itemx -munaligned-doubles |
| @opindex mno-unaligned-doubles |
| @opindex munaligned-doubles |
| Assume that doubles have 8-byte alignment. This is the default. |
| |
| With @option{-munaligned-doubles}, GCC assumes that doubles have 8-byte |
| alignment only if they are contained in another type, or if they have an |
| absolute address. Otherwise, it assumes they have 4-byte alignment. |
| Specifying this option avoids some rare compatibility problems with code |
| generated by other compilers. It is not the default because it results |
| in a performance loss, especially for floating-point code. |
| |
| @item -mno-faster-structs |
| @itemx -mfaster-structs |
| @opindex mno-faster-structs |
| @opindex mfaster-structs |
| With @option{-mfaster-structs}, the compiler assumes that structures |
| should have 8-byte alignment. This enables the use of pairs of |
| @code{ldd} and @code{std} instructions for copies in structure |
| assignment, in place of twice as many @code{ld} and @code{st} pairs. |
| However, the use of this changed alignment directly violates the SPARC |
| ABI@. Thus, it's intended only for use on targets where the developer |
| acknowledges that their resulting code is not directly in line with |
| the rules of the ABI@. |
| |
| @item -mcpu=@var{cpu_type} |
| @opindex mcpu |
| Set the instruction set, register set, and instruction scheduling parameters |
| for machine type @var{cpu_type}. Supported values for @var{cpu_type} are |
| @samp{v7}, @samp{cypress}, @samp{v8}, @samp{supersparc}, @samp{hypersparc}, |
| @samp{leon}, @samp{sparclite}, @samp{f930}, @samp{f934}, @samp{sparclite86x}, |
| @samp{sparclet}, @samp{tsc701}, @samp{v9}, @samp{ultrasparc}, |
| @samp{ultrasparc3}, @samp{niagara}, @samp{niagara2}, @samp{niagara3}, |
| and @samp{niagara4}. |
| |
| Native Solaris and GNU/Linux toolchains also support the value @samp{native}, |
| which selects the best architecture option for the host processor. |
| @option{-mcpu=native} has no effect if GCC does not recognize |
| the processor. |
| |
| Default instruction scheduling parameters are used for values that select |
| an architecture and not an implementation. These are @samp{v7}, @samp{v8}, |
| @samp{sparclite}, @samp{sparclet}, @samp{v9}. |
| |
| Here is a list of each supported architecture and their supported |
| implementations. |
| |
| @table @asis |
| @item v7 |
| cypress |
| |
| @item v8 |
| supersparc, hypersparc, leon |
| |
| @item sparclite |
| f930, f934, sparclite86x |
| |
| @item sparclet |
| tsc701 |
| |
| @item v9 |
| ultrasparc, ultrasparc3, niagara, niagara2, niagara3, niagara4 |
| @end table |
| |
| By default (unless configured otherwise), GCC generates code for the V7 |
| variant of the SPARC architecture. With @option{-mcpu=cypress}, the compiler |
| additionally optimizes it for the Cypress CY7C602 chip, as used in the |
| SPARCStation/SPARCServer 3xx series. This is also appropriate for the older |
| SPARCStation 1, 2, IPX etc. |
| |
| With @option{-mcpu=v8}, GCC generates code for the V8 variant of the SPARC |
| architecture. The only difference from V7 code is that the compiler emits |
| the integer multiply and integer divide instructions which exist in SPARC-V8 |
| but not in SPARC-V7. With @option{-mcpu=supersparc}, the compiler additionally |
| optimizes it for the SuperSPARC chip, as used in the SPARCStation 10, 1000 and |
| 2000 series. |
| |
| With @option{-mcpu=sparclite}, GCC generates code for the SPARClite variant of |
| the SPARC architecture. This adds the integer multiply, integer divide step |
| and scan (@code{ffs}) instructions which exist in SPARClite but not in SPARC-V7. |
| With @option{-mcpu=f930}, the compiler additionally optimizes it for the |
| Fujitsu MB86930 chip, which is the original SPARClite, with no FPU@. With |
| @option{-mcpu=f934}, the compiler additionally optimizes it for the Fujitsu |
| MB86934 chip, which is the more recent SPARClite with FPU@. |
| |
| With @option{-mcpu=sparclet}, GCC generates code for the SPARClet variant of |
| the SPARC architecture. This adds the integer multiply, multiply/accumulate, |
| integer divide step and scan (@code{ffs}) instructions which exist in SPARClet |
| but not in SPARC-V7. With @option{-mcpu=tsc701}, the compiler additionally |
| optimizes it for the TEMIC SPARClet chip. |
| |
| With @option{-mcpu=v9}, GCC generates code for the V9 variant of the SPARC |
| architecture. This adds 64-bit integer and floating-point move instructions, |
| 3 additional floating-point condition code registers and conditional move |
| instructions. With @option{-mcpu=ultrasparc}, the compiler additionally |
| optimizes it for the Sun UltraSPARC I/II/IIi chips. With |
| @option{-mcpu=ultrasparc3}, the compiler additionally optimizes it for the |
| Sun UltraSPARC III/III+/IIIi/IIIi+/IV/IV+ chips. With |
| @option{-mcpu=niagara}, the compiler additionally optimizes it for |
| Sun UltraSPARC T1 chips. With @option{-mcpu=niagara2}, the compiler |
| additionally optimizes it for Sun UltraSPARC T2 chips. With |
| @option{-mcpu=niagara3}, the compiler additionally optimizes it for Sun |
| UltraSPARC T3 chips. With @option{-mcpu=niagara4}, the compiler |
| additionally optimizes it for Sun UltraSPARC T4 chips. |
| |
| @item -mtune=@var{cpu_type} |
| @opindex mtune |
| Set the instruction scheduling parameters for machine type |
| @var{cpu_type}, but do not set the instruction set or register set that the |
| option @option{-mcpu=@var{cpu_type}} does. |
| |
| The same values for @option{-mcpu=@var{cpu_type}} can be used for |
| @option{-mtune=@var{cpu_type}}, but the only useful values are those |
| that select a particular CPU implementation. Those are @samp{cypress}, |
| @samp{supersparc}, @samp{hypersparc}, @samp{leon}, @samp{f930}, @samp{f934}, |
| @samp{sparclite86x}, @samp{tsc701}, @samp{ultrasparc}, @samp{ultrasparc3}, |
| @samp{niagara}, @samp{niagara2}, @samp{niagara3} and @samp{niagara4}. With |
| native Solaris and GNU/Linux toolchains, @samp{native} can also be used. |
| |
| @item -mv8plus |
| @itemx -mno-v8plus |
| @opindex mv8plus |
| @opindex mno-v8plus |
| With @option{-mv8plus}, GCC generates code for the SPARC-V8+ ABI@. The |
| difference from the V8 ABI is that the global and out registers are |
| considered 64 bits wide. This is enabled by default on Solaris in 32-bit |
| mode for all SPARC-V9 processors. |
| |
| @item -mvis |
| @itemx -mno-vis |
| @opindex mvis |
| @opindex mno-vis |
| With @option{-mvis}, GCC generates code that takes advantage of the UltraSPARC |
| Visual Instruction Set extensions. The default is @option{-mno-vis}. |
| |
| @item -mvis2 |
| @itemx -mno-vis2 |
| @opindex mvis2 |
| @opindex mno-vis2 |
| With @option{-mvis2}, GCC generates code that takes advantage of |
| version 2.0 of the UltraSPARC Visual Instruction Set extensions. The |
| default is @option{-mvis2} when targeting a cpu that supports such |
| instructions, such as UltraSPARC-III and later. Setting @option{-mvis2} |
| also sets @option{-mvis}. |
| |
| @item -mvis3 |
| @itemx -mno-vis3 |
| @opindex mvis3 |
| @opindex mno-vis3 |
| With @option{-mvis3}, GCC generates code that takes advantage of |
| version 3.0 of the UltraSPARC Visual Instruction Set extensions. The |
| default is @option{-mvis3} when targeting a cpu that supports such |
| instructions, such as niagara-3 and later. Setting @option{-mvis3} |
| also sets @option{-mvis2} and @option{-mvis}. |
| |
| @item -mpopc |
| @itemx -mno-popc |
| @opindex mpopc |
| @opindex mno-popc |
| With @option{-mpopc}, GCC generates code that takes advantage of the UltraSPARC |
| population count instruction. The default is @option{-mpopc} |
| when targeting a cpu that supports such instructions, such as Niagara-2 and |
| later. |
| |
| @item -mfmaf |
| @itemx -mno-fmaf |
| @opindex mfmaf |
| @opindex mno-fmaf |
| With @option{-mfmaf}, GCC generates code that takes advantage of the UltraSPARC |
| Fused Multiply-Add Floating-point extensions. The default is @option{-mfmaf} |
| when targeting a cpu that supports such instructions, such as Niagara-3 and |
| later. |
| |
| @item -mfix-at697f |
| @opindex mfix-at697f |
| Enable the documented workaround for the single erratum of the Atmel AT697F |
| processor (which corresponds to erratum #13 of the AT697E processor). |
| @end table |
| |
| These @samp{-m} options are supported in addition to the above |
| on SPARC-V9 processors in 64-bit environments: |
| |
| @table @gcctabopt |
| @item -mlittle-endian |
| @opindex mlittle-endian |
| Generate code for a processor running in little-endian mode. It is only |
| available for a few configurations and most notably not on Solaris and Linux. |
| |
| @item -m32 |
| @itemx -m64 |
| @opindex m32 |
| @opindex m64 |
| Generate code for a 32-bit or 64-bit environment. |
| The 32-bit environment sets int, long and pointer to 32 bits. |
| The 64-bit environment sets int to 32 bits and long and pointer |
| to 64 bits. |
| |
| @item -mcmodel=@var{which} |
| @opindex mcmodel |
| Set the code model to one of |
| |
| @table @samp |
| @item medlow |
| The Medium/Low code model: 64-bit addresses, programs |
| must be linked in the low 32 bits of memory. Programs can be statically |
| or dynamically linked. |
| |
| @item medmid |
| The Medium/Middle code model: 64-bit addresses, programs |
| must be linked in the low 44 bits of memory, the text and data segments must |
| be less than 2GB in size and the data segment must be located within 2GB of |
| the text segment. |
| |
| @item medany |
| The Medium/Anywhere code model: 64-bit addresses, programs |
| may be linked anywhere in memory, the text and data segments must be less |
| than 2GB in size and the data segment must be located within 2GB of the |
| text segment. |
| |
| @item embmedany |
| The Medium/Anywhere code model for embedded systems: |
| 64-bit addresses, the text and data segments must be less than 2GB in |
| size, both starting anywhere in memory (determined at link time). The |
| global register %g4 points to the base of the data segment. Programs |
| are statically linked and PIC is not supported. |
| @end table |
| |
| @item -mmemory-model=@var{mem-model} |
| @opindex mmemory-model |
| Set the memory model in force on the processor to one of |
| |
| @table @samp |
| @item default |
| The default memory model for the processor and operating system. |
| |
| @item rmo |
| Relaxed Memory Order |
| |
| @item pso |
| Partial Store Order |
| |
| @item tso |
| Total Store Order |
| |
| @item sc |
| Sequential Consistency |
| @end table |
| |
| These memory models are formally defined in Appendix D of the Sparc V9 |
| architecture manual, as set in the processor's @code{PSTATE.MM} field. |
| |
| @item -mstack-bias |
| @itemx -mno-stack-bias |
| @opindex mstack-bias |
| @opindex mno-stack-bias |
| With @option{-mstack-bias}, GCC assumes that the stack pointer, and |
| frame pointer if present, are offset by @minus{}2047 which must be added back |
| when making stack frame references. This is the default in 64-bit mode. |
| Otherwise, assume no such offset is present. |
| @end table |
| |
| @node SPU Options |
| @subsection SPU Options |
| @cindex SPU options |
| |
| These @samp{-m} options are supported on the SPU: |
| |
| @table @gcctabopt |
| @item -mwarn-reloc |
| @itemx -merror-reloc |
| @opindex mwarn-reloc |
| @opindex merror-reloc |
| |
| The loader for SPU does not handle dynamic relocations. By default, GCC |
| gives an error when it generates code that requires a dynamic |
| relocation. @option{-mno-error-reloc} disables the error, |
| @option{-mwarn-reloc} generates a warning instead. |
| |
| @item -msafe-dma |
| @itemx -munsafe-dma |
| @opindex msafe-dma |
| @opindex munsafe-dma |
| |
| Instructions that initiate or test completion of DMA must not be |
| reordered with respect to loads and stores of the memory that is being |
| accessed. |
| With @option{-munsafe-dma} you must use the @code{volatile} keyword to protect |
| memory accesses, but that can lead to inefficient code in places where the |
| memory is known to not change. Rather than mark the memory as volatile, |
| you can use @option{-msafe-dma} to tell the compiler to treat |
| the DMA instructions as potentially affecting all memory. |
| |
| @item -mbranch-hints |
| @opindex mbranch-hints |
| |
| By default, GCC generates a branch hint instruction to avoid |
| pipeline stalls for always-taken or probably-taken branches. A hint |
| is not generated closer than 8 instructions away from its branch. |
| There is little reason to disable them, except for debugging purposes, |
| or to make an object a little bit smaller. |
| |
| @item -msmall-mem |
| @itemx -mlarge-mem |
| @opindex msmall-mem |
| @opindex mlarge-mem |
| |
| By default, GCC generates code assuming that addresses are never larger |
| than 18 bits. With @option{-mlarge-mem} code is generated that assumes |
| a full 32-bit address. |
| |
| @item -mstdmain |
| @opindex mstdmain |
| |
| By default, GCC links against startup code that assumes the SPU-style |
| main function interface (which has an unconventional parameter list). |
| With @option{-mstdmain}, GCC links your program against startup |
| code that assumes a C99-style interface to @code{main}, including a |
| local copy of @code{argv} strings. |
| |
| @item -mfixed-range=@var{register-range} |
| @opindex mfixed-range |
| Generate code treating the given register range as fixed registers. |
| A fixed register is one that the register allocator cannot use. This is |
| useful when compiling kernel code. A register range is specified as |
| two registers separated by a dash. Multiple register ranges can be |
| specified separated by a comma. |
| |
| @item -mea32 |
| @itemx -mea64 |
| @opindex mea32 |
| @opindex mea64 |
| Compile code assuming that pointers to the PPU address space accessed |
| via the @code{__ea} named address space qualifier are either 32 or 64 |
| bits wide. The default is 32 bits. As this is an ABI-changing option, |
| all object code in an executable must be compiled with the same setting. |
| |
| @item -maddress-space-conversion |
| @itemx -mno-address-space-conversion |
| @opindex maddress-space-conversion |
| @opindex mno-address-space-conversion |
| Allow/disallow treating the @code{__ea} address space as superset |
| of the generic address space. This enables explicit type casts |
| between @code{__ea} and generic pointer as well as implicit |
| conversions of generic pointers to @code{__ea} pointers. The |
| default is to allow address space pointer conversions. |
| |
| @item -mcache-size=@var{cache-size} |
| @opindex mcache-size |
| This option controls the version of libgcc that the compiler links to an |
| executable and selects a software-managed cache for accessing variables |
| in the @code{__ea} address space with a particular cache size. Possible |
| options for @var{cache-size} are @samp{8}, @samp{16}, @samp{32}, @samp{64} |
| and @samp{128}. The default cache size is 64KB. |
| |
| @item -matomic-updates |
| @itemx -mno-atomic-updates |
| @opindex matomic-updates |
| @opindex mno-atomic-updates |
| This option controls the version of libgcc that the compiler links to an |
| executable and selects whether atomic updates to the software-managed |
| cache of PPU-side variables are used. If you use atomic updates, changes |
| to a PPU variable from SPU code using the @code{__ea} named address space |
| qualifier do not interfere with changes to other PPU variables residing |
| in the same cache line from PPU code. If you do not use atomic updates, |
| such interference may occur; however, writing back cache lines is |
| more efficient. The default behavior is to use atomic updates. |
| |
| @item -mdual-nops |
| @itemx -mdual-nops=@var{n} |
| @opindex mdual-nops |
| By default, GCC inserts nops to increase dual issue when it expects |
| it to increase performance. @var{n} can be a value from 0 to 10. A |
| smaller @var{n} inserts fewer nops. 10 is the default, 0 is the |
| same as @option{-mno-dual-nops}. Disabled with @option{-Os}. |
| |
| @item -mhint-max-nops=@var{n} |
| @opindex mhint-max-nops |
| Maximum number of nops to insert for a branch hint. A branch hint must |
| be at least 8 instructions away from the branch it is affecting. GCC |
| inserts up to @var{n} nops to enforce this, otherwise it does not |
| generate the branch hint. |
| |
| @item -mhint-max-distance=@var{n} |
| @opindex mhint-max-distance |
| The encoding of the branch hint instruction limits the hint to be within |
| 256 instructions of the branch it is affecting. By default, GCC makes |
| sure it is within 125. |
| |
| @item -msafe-hints |
| @opindex msafe-hints |
| Work around a hardware bug that causes the SPU to stall indefinitely. |
| By default, GCC inserts the @code{hbrp} instruction to make sure |
| this stall won't happen. |
| |
| @end table |
| |
| @node System V Options |
| @subsection Options for System V |
| |
| These additional options are available on System V Release 4 for |
| compatibility with other compilers on those systems: |
| |
| @table @gcctabopt |
| @item -G |
| @opindex G |
| Create a shared object. |
| It is recommended that @option{-symbolic} or @option{-shared} be used instead. |
| |
| @item -Qy |
| @opindex Qy |
| Identify the versions of each tool used by the compiler, in a |
| @code{.ident} assembler directive in the output. |
| |
| @item -Qn |
| @opindex Qn |
| Refrain from adding @code{.ident} directives to the output file (this is |
| the default). |
| |
| @item -YP,@var{dirs} |
| @opindex YP |
| Search the directories @var{dirs}, and no others, for libraries |
| specified with @option{-l}. |
| |
| @item -Ym,@var{dir} |
| @opindex Ym |
| Look in the directory @var{dir} to find the M4 preprocessor. |
| The assembler uses this option. |
| @c This is supposed to go with a -Yd for predefined M4 macro files, but |
| @c the generic assembler that comes with Solaris takes just -Ym. |
| @end table |
| |
| @node TILE-Gx Options |
| @subsection TILE-Gx Options |
| @cindex TILE-Gx options |
| |
| These @samp{-m} options are supported on the TILE-Gx: |
| |
| @table @gcctabopt |
| @item -mcmodel=small |
| @opindex mcmodel=small |
| Generate code for the small model. The distance for direct calls is |
| limited to 500M in either direction. PC-relative addresses are 32 |
| bits. Absolute addresses support the full address range. |
| |
| @item -mcmodel=large |
| @opindex mcmodel=large |
| Generate code for the large model. There is no limitation on call |
| distance, pc-relative addresses, or absolute addresses. |
| |
| @item -mcpu=@var{name} |
| @opindex mcpu |
| Selects the type of CPU to be targeted. Currently the only supported |
| type is @samp{tilegx}. |
| |
| @item -m32 |
| @itemx -m64 |
| @opindex m32 |
| @opindex m64 |
| Generate code for a 32-bit or 64-bit environment. The 32-bit |
| environment sets int, long, and pointer to 32 bits. The 64-bit |
| environment sets int to 32 bits and long and pointer to 64 bits. |
| @end table |
| |
| @node TILEPro Options |
| @subsection TILEPro Options |
| @cindex TILEPro options |
| |
| These @samp{-m} options are supported on the TILEPro: |
| |
| @table @gcctabopt |
| @item -mcpu=@var{name} |
| @opindex mcpu |
| Selects the type of CPU to be targeted. Currently the only supported |
| type is @samp{tilepro}. |
| |
| @item -m32 |
| @opindex m32 |
| Generate code for a 32-bit environment, which sets int, long, and |
| pointer to 32 bits. This is the only supported behavior so the flag |
| is essentially ignored. |
| @end table |
| |
| @node V850 Options |
| @subsection V850 Options |
| @cindex V850 Options |
| |
| These @samp{-m} options are defined for V850 implementations: |
| |
| @table @gcctabopt |
| @item -mlong-calls |
| @itemx -mno-long-calls |
| @opindex mlong-calls |
| @opindex mno-long-calls |
| Treat all calls as being far away (near). If calls are assumed to be |
| far away, the compiler always loads the function's address into a |
| register, and calls indirect through the pointer. |
| |
| @item -mno-ep |
| @itemx -mep |
| @opindex mno-ep |
| @opindex mep |
| Do not optimize (do optimize) basic blocks that use the same index |
| pointer 4 or more times to copy pointer into the @code{ep} register, and |
| use the shorter @code{sld} and @code{sst} instructions. The @option{-mep} |
| option is on by default if you optimize. |
| |
| @item -mno-prolog-function |
| @itemx -mprolog-function |
| @opindex mno-prolog-function |
| @opindex mprolog-function |
| Do not use (do use) external functions to save and restore registers |
| at the prologue and epilogue of a function. The external functions |
| are slower, but use less code space if more than one function saves |
| the same number of registers. The @option{-mprolog-function} option |
| is on by default if you optimize. |
| |
| @item -mspace |
| @opindex mspace |
| Try to make the code as small as possible. At present, this just turns |
| on the @option{-mep} and @option{-mprolog-function} options. |
| |
| @item -mtda=@var{n} |
| @opindex mtda |
| Put static or global variables whose size is @var{n} bytes or less into |
| the tiny data area that register @code{ep} points to. The tiny data |
| area can hold up to 256 bytes in total (128 bytes for byte references). |
| |
| @item -msda=@var{n} |
| @opindex msda |
| Put static or global variables whose size is @var{n} bytes or less into |
| the small data area that register @code{gp} points to. The small data |
| area can hold up to 64 kilobytes. |
| |
| @item -mzda=@var{n} |
| @opindex mzda |
| Put static or global variables whose size is @var{n} bytes or less into |
| the first 32 kilobytes of memory. |
| |
| @item -mv850 |
| @opindex mv850 |
| Specify that the target processor is the V850. |
| |
| @item -mbig-switch |
| @opindex mbig-switch |
| Generate code suitable for big switch tables. Use this option only if |
| the assembler/linker complain about out of range branches within a switch |
| table. |
| |
| @item -mapp-regs |
| @opindex mapp-regs |
| This option causes r2 and r5 to be used in the code generated by |
| the compiler. This setting is the default. |
| |
| @item -mno-app-regs |
| @opindex mno-app-regs |
| This option causes r2 and r5 to be treated as fixed registers. |
| |
| @item -mv850e2v3 |
| @opindex mv850e2v3 |
| Specify that the target processor is the V850E2V3. The preprocessor |
| constant @samp{__v850e2v3__} is defined if |
| this option is used. |
| |
| @item -mv850e2 |
| @opindex mv850e2 |
| Specify that the target processor is the V850E2. The preprocessor |
| constant @samp{__v850e2__} is defined if this option is used. |
| |
| @item -mv850e1 |
| @opindex mv850e1 |
| Specify that the target processor is the V850E1. The preprocessor |
| constants @samp{__v850e1__} and @samp{__v850e__} are defined if |
| this option is used. |
| |
| @item -mv850es |
| @opindex mv850es |
| Specify that the target processor is the V850ES. This is an alias for |
| the @option{-mv850e1} option. |
| |
| @item -mv850e |
| @opindex mv850e |
| Specify that the target processor is the V850E@. The preprocessor |
| constant @samp{__v850e__} is defined if this option is used. |
| |
| If neither @option{-mv850} nor @option{-mv850e} nor @option{-mv850e1} |
| nor @option{-mv850e2} nor @option{-mv850e2v3} |
| are defined then a default target processor is chosen and the |
| relevant @samp{__v850*__} preprocessor constant is defined. |
| |
| The preprocessor constants @samp{__v850} and @samp{__v851__} are always |
| defined, regardless of which processor variant is the target. |
| |
| @item -mdisable-callt |
| @opindex mdisable-callt |
| This option suppresses generation of the @code{CALLT} instruction for the |
| v850e, v850e1, v850e2 and v850e2v3 flavors of the v850 architecture. The default is |
| @option{-mno-disable-callt} which allows the @code{CALLT} instruction to be used. |
| |
| @end table |
| |
| @node VAX Options |
| @subsection VAX Options |
| @cindex VAX options |
| |
| These @samp{-m} options are defined for the VAX: |
| |
| @table @gcctabopt |
| @item -munix |
| @opindex munix |
| Do not output certain jump instructions (@code{aobleq} and so on) |
| that the Unix assembler for the VAX cannot handle across long |
| ranges. |
| |
| @item -mgnu |
| @opindex mgnu |
| Do output those jump instructions, on the assumption that the |
| GNU assembler is being used. |
| |
| @item -mg |
| @opindex mg |
| Output code for G-format floating-point numbers instead of D-format. |
| @end table |
| |
| @node VMS Options |
| @subsection VMS Options |
| |
| These @samp{-m} options are defined for the VMS implementations: |
| |
| @table @gcctabopt |
| @item -mvms-return-codes |
| @opindex mvms-return-codes |
| Return VMS condition codes from @code{main}. The default is to return POSIX-style |
| condition (e.g.@ error) codes. |
| |
| @item -mdebug-main=@var{prefix} |
| @opindex mdebug-main=@var{prefix} |
| Flag the first routine whose name starts with @var{prefix} as the main |
| routine for the debugger. |
| |
| @item -mmalloc64 |
| @opindex mmalloc64 |
| Default to 64-bit memory allocation routines. |
| |
| @item -mpointer-size=@var{size} |
| @opindex -mpointer-size=@var{size} |
| Set the default size of pointers. Possible options for @var{size} are |
| @samp{32} or @samp{short} for 32 bit pointers, @samp{64} or @samp{long} |
| for 64 bit pointers, and @samp{no} for supporting only 32 bit pointers. |
| The later option disables @code{pragma pointer_size}. |
| @end table |
| |
| @node VxWorks Options |
| @subsection VxWorks Options |
| @cindex VxWorks Options |
| |
| The options in this section are defined for all VxWorks targets. |
| Options specific to the target hardware are listed with the other |
| options for that target. |
| |
| @table @gcctabopt |
| @item -mrtp |
| @opindex mrtp |
| GCC can generate code for both VxWorks kernels and real time processes |
| (RTPs). This option switches from the former to the latter. It also |
| defines the preprocessor macro @code{__RTP__}. |
| |
| @item -non-static |
| @opindex non-static |
| Link an RTP executable against shared libraries rather than static |
| libraries. The options @option{-static} and @option{-shared} can |
| also be used for RTPs (@pxref{Link Options}); @option{-static} |
| is the default. |
| |
| @item -Bstatic |
| @itemx -Bdynamic |
| @opindex Bstatic |
| @opindex Bdynamic |
| These options are passed down to the linker. They are defined for |
| compatibility with Diab. |
| |
| @item -Xbind-lazy |
| @opindex Xbind-lazy |
| Enable lazy binding of function calls. This option is equivalent to |
| @option{-Wl,-z,now} and is defined for compatibility with Diab. |
| |
| @item -Xbind-now |
| @opindex Xbind-now |
| Disable lazy binding of function calls. This option is the default and |
| is defined for compatibility with Diab. |
| @end table |
| |
| @node x86-64 Options |
| @subsection x86-64 Options |
| @cindex x86-64 options |
| |
| These are listed under @xref{i386 and x86-64 Options}. |
| |
| @node Xstormy16 Options |
| @subsection Xstormy16 Options |
| @cindex Xstormy16 Options |
| |
| These options are defined for Xstormy16: |
| |
| @table @gcctabopt |
| @item -msim |
| @opindex msim |
| Choose startup files and linker script suitable for the simulator. |
| @end table |
| |
| @node Xtensa Options |
| @subsection Xtensa Options |
| @cindex Xtensa Options |
| |
| These options are supported for Xtensa targets: |
| |
| @table @gcctabopt |
| @item -mconst16 |
| @itemx -mno-const16 |
| @opindex mconst16 |
| @opindex mno-const16 |
| Enable or disable use of @code{CONST16} instructions for loading |
| constant values. The @code{CONST16} instruction is currently not a |
| standard option from Tensilica. When enabled, @code{CONST16} |
| instructions are always used in place of the standard @code{L32R} |
| instructions. The use of @code{CONST16} is enabled by default only if |
| the @code{L32R} instruction is not available. |
| |
| @item -mfused-madd |
| @itemx -mno-fused-madd |
| @opindex mfused-madd |
| @opindex mno-fused-madd |
| Enable or disable use of fused multiply/add and multiply/subtract |
| instructions in the floating-point option. This has no effect if the |
| floating-point option is not also enabled. Disabling fused multiply/add |
| and multiply/subtract instructions forces the compiler to use separate |
| instructions for the multiply and add/subtract operations. This may be |
| desirable in some cases where strict IEEE 754-compliant results are |
| required: the fused multiply add/subtract instructions do not round the |
| intermediate result, thereby producing results with @emph{more} bits of |
| precision than specified by the IEEE standard. Disabling fused multiply |
| add/subtract instructions also ensures that the program output is not |
| sensitive to the compiler's ability to combine multiply and add/subtract |
| operations. |
| |
| @item -mserialize-volatile |
| @itemx -mno-serialize-volatile |
| @opindex mserialize-volatile |
| @opindex mno-serialize-volatile |
| When this option is enabled, GCC inserts @code{MEMW} instructions before |
| @code{volatile} memory references to guarantee sequential consistency. |
| The default is @option{-mserialize-volatile}. Use |
| @option{-mno-serialize-volatile} to omit the @code{MEMW} instructions. |
| |
| @item -mforce-no-pic |
| @opindex mforce-no-pic |
| For targets, like GNU/Linux, where all user-mode Xtensa code must be |
| position-independent code (PIC), this option disables PIC for compiling |
| kernel code. |
| |
| @item -mtext-section-literals |
| @itemx -mno-text-section-literals |
| @opindex mtext-section-literals |
| @opindex mno-text-section-literals |
| Control the treatment of literal pools. The default is |
| @option{-mno-text-section-literals}, which places literals in a separate |
| section in the output file. This allows the literal pool to be placed |
| in a data RAM/ROM, and it also allows the linker to combine literal |
| pools from separate object files to remove redundant literals and |
| improve code size. With @option{-mtext-section-literals}, the literals |
| are interspersed in the text section in order to keep them as close as |
| possible to their references. This may be necessary for large assembly |
| files. |
| |
| @item -mtarget-align |
| @itemx -mno-target-align |
| @opindex mtarget-align |
| @opindex mno-target-align |
| When this option is enabled, GCC instructs the assembler to |
| automatically align instructions to reduce branch penalties at the |
| expense of some code density. The assembler attempts to widen density |
| instructions to align branch targets and the instructions following call |
| instructions. If there are not enough preceding safe density |
| instructions to align a target, no widening is performed. The |
| default is @option{-mtarget-align}. These options do not affect the |
| treatment of auto-aligned instructions like @code{LOOP}, which the |
| assembler always aligns, either by widening density instructions or |
| by inserting NOP instructions. |
| |
| @item -mlongcalls |
| @itemx -mno-longcalls |
| @opindex mlongcalls |
| @opindex mno-longcalls |
| When this option is enabled, GCC instructs the assembler to translate |
| direct calls to indirect calls unless it can determine that the target |
| of a direct call is in the range allowed by the call instruction. This |
| translation typically occurs for calls to functions in other source |
| files. Specifically, the assembler translates a direct @code{CALL} |
| instruction into an @code{L32R} followed by a @code{CALLX} instruction. |
| The default is @option{-mno-longcalls}. This option should be used in |
| programs where the call target can potentially be out of range. This |
| option is implemented in the assembler, not the compiler, so the |
| assembly code generated by GCC still shows direct call |
| instructions---look at the disassembled object code to see the actual |
| instructions. Note that the assembler uses an indirect call for |
| every cross-file call, not just those that really are out of range. |
| @end table |
| |
| @node zSeries Options |
| @subsection zSeries Options |
| @cindex zSeries options |
| |
| These are listed under @xref{S/390 and zSeries Options}. |
| |
| @node Code Gen Options |
| @section Options for Code Generation Conventions |
| @cindex code generation conventions |
| @cindex options, code generation |
| @cindex run-time options |
| |
| These machine-independent options control the interface conventions |
| used in code generation. |
| |
| Most of them have both positive and negative forms; the negative form |
| of @option{-ffoo} is @option{-fno-foo}. In the table below, only |
| one of the forms is listed---the one that is not the default. You |
| can figure out the other form by either removing @samp{no-} or adding |
| it. |
| |
| @table @gcctabopt |
| @item -fbounds-check |
| @opindex fbounds-check |
| For front ends that support it, generate additional code to check that |
| indices used to access arrays are within the declared range. This is |
| currently only supported by the Java and Fortran front ends, where |
| this option defaults to true and false respectively. |
| |
| @item -fstack-reuse=@var{reuse-level} |
| @opindex fstack_reuse |
| This option controls stack space reuse for user declared local/auto variables |
| and compiler generated temporaries. @var{reuse_level} can be @samp{all}, |
| @samp{named_vars}, or @samp{none}. @samp{all} enables stack reuse for all |
| local variables and temporaries, @samp{named_vars} enables the reuse only for |
| user defined local variables with names, and @samp{none} disables stack reuse |
| completely. The default value is @samp{all}. The option is needed when the |
| program extends the lifetime of a scoped local variable or a compiler generated |
| temporary beyond the end point defined by the language. When a lifetime of |
| a variable ends, and if the variable lives in memory, the optimizing compiler |
| has the freedom to reuse its stack space with other temporaries or scoped |
| local variables whose live range does not overlap with it. Legacy code extending |
| local lifetime will likely to break with the stack reuse optimization. |
| |
| For example, |
| |
| @smallexample |
| int *p; |
| @{ |
| int local1; |
| |
| p = &local1; |
| local1 = 10; |
| .... |
| @} |
| @{ |
| int local2; |
| local2 = 20; |
| ... |
| @} |
| |
| if (*p == 10) // out of scope use of local1 |
| @{ |
| |
| @} |
| @end smallexample |
| |
| Another example: |
| @smallexample |
| |
| struct A |
| @{ |
| A(int k) : i(k), j(k) @{ @} |
| int i; |
| int j; |
| @}; |
| |
| A *ap; |
| |
| void foo(const A& ar) |
| @{ |
| ap = &ar; |
| @} |
| |
| void bar() |
| @{ |
| foo(A(10)); // temp object's lifetime ends when foo returns |
| |
| @{ |
| A a(20); |
| .... |
| @} |
| ap->i+= 10; // ap references out of scope temp whose space |
| // is reused with a. What is the value of ap->i? |
| @} |
| |
| @end smallexample |
| |
| The lifetime of a compiler generated temporary is well defined by the C++ |
| standard. When a lifetime of a temporary ends, and if the temporary lives |
| in memory, the optimizing compiler has the freedom to reuse its stack |
| space with other temporaries or scoped local variables whose live range |
| does not overlap with it. However some of the legacy code relies on |
| the behavior of older compilers in which temporaries' stack space is |
| not reused, the aggressive stack reuse can lead to runtime errors. This |
| option is used to control the temporary stack reuse optimization. |
| |
| @item -ftrapv |
| @opindex ftrapv |
| This option generates traps for signed overflow on addition, subtraction, |
| multiplication operations. |
| |
| @item -fwrapv |
| @opindex fwrapv |
| This option instructs the compiler to assume that signed arithmetic |
| overflow of addition, subtraction and multiplication wraps around |
| using twos-complement representation. This flag enables some optimizations |
| and disables others. This option is enabled by default for the Java |
| front end, as required by the Java language specification. |
| |
| @item -fexceptions |
| @opindex fexceptions |
| Enable exception handling. Generates extra code needed to propagate |
| exceptions. For some targets, this implies GCC generates frame |
| unwind information for all functions, which can produce significant data |
| size overhead, although it does not affect execution. If you do not |
| specify this option, GCC enables it by default for languages like |
| C++ that normally require exception handling, and disables it for |
| languages like C that do not normally require it. However, you may need |
| to enable this option when compiling C code that needs to interoperate |
| properly with exception handlers written in C++. You may also wish to |
| disable this option if you are compiling older C++ programs that don't |
| use exception handling. |
| |
| @item -fnon-call-exceptions |
| @opindex fnon-call-exceptions |
| Generate code that allows trapping instructions to throw exceptions. |
| Note that this requires platform-specific runtime support that does |
| not exist everywhere. Moreover, it only allows @emph{trapping} |
| instructions to throw exceptions, i.e.@: memory references or floating-point |
| instructions. It does not allow exceptions to be thrown from |
| arbitrary signal handlers such as @code{SIGALRM}. |
| |
| @item -fdelete-dead-exceptions |
| @opindex fdelete-dead-exceptions |
| Consider that instructions that may throw exceptions but don't otherwise |
| contribute to the execution of the program can be optimized away. |
| This option is enabled by default for the Ada front end, as permitted by |
| the Ada language specification. |
| Optimization passes that cause dead exceptions to be removed are enabled independently at different optimization levels. |
| |
| @item -funwind-tables |
| @opindex funwind-tables |
| Similar to @option{-fexceptions}, except that it just generates any needed |
| static data, but does not affect the generated code in any other way. |
| You normally do not need to enable this option; instead, a language processor |
| that needs this handling enables it on your behalf. |
| |
| @item -fasynchronous-unwind-tables |
| @opindex fasynchronous-unwind-tables |
| Generate unwind table in DWARF 2 format, if supported by target machine. The |
| table is exact at each instruction boundary, so it can be used for stack |
| unwinding from asynchronous events (such as debugger or garbage collector). |
| |
| @item -fpcc-struct-return |
| @opindex fpcc-struct-return |
| Return ``short'' @code{struct} and @code{union} values in memory like |
| longer ones, rather than in registers. This convention is less |
| efficient, but it has the advantage of allowing intercallability between |
| GCC-compiled files and files compiled with other compilers, particularly |
| the Portable C Compiler (pcc). |
| |
| The precise convention for returning structures in memory depends |
| on the target configuration macros. |
| |
| Short structures and unions are those whose size and alignment match |
| that of some integer type. |
| |
| @strong{Warning:} code compiled with the @option{-fpcc-struct-return} |
| switch is not binary compatible with code compiled with the |
| @option{-freg-struct-return} switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -freg-struct-return |
| @opindex freg-struct-return |
| Return @code{struct} and @code{union} values in registers when possible. |
| This is more efficient for small structures than |
| @option{-fpcc-struct-return}. |
| |
| If you specify neither @option{-fpcc-struct-return} nor |
| @option{-freg-struct-return}, GCC defaults to whichever convention is |
| standard for the target. If there is no standard convention, GCC |
| defaults to @option{-fpcc-struct-return}, except on targets where GCC is |
| the principal compiler. In those cases, we can choose the standard, and |
| we chose the more efficient register return alternative. |
| |
| @strong{Warning:} code compiled with the @option{-freg-struct-return} |
| switch is not binary compatible with code compiled with the |
| @option{-fpcc-struct-return} switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fshort-enums |
| @opindex fshort-enums |
| Allocate to an @code{enum} type only as many bytes as it needs for the |
| declared range of possible values. Specifically, the @code{enum} type |
| is equivalent to the smallest integer type that has enough room. |
| |
| @strong{Warning:} the @option{-fshort-enums} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fshort-double |
| @opindex fshort-double |
| Use the same size for @code{double} as for @code{float}. |
| |
| @strong{Warning:} the @option{-fshort-double} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fshort-wchar |
| @opindex fshort-wchar |
| Override the underlying type for @samp{wchar_t} to be @samp{short |
| unsigned int} instead of the default for the target. This option is |
| useful for building programs to run under WINE@. |
| |
| @strong{Warning:} the @option{-fshort-wchar} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -fno-common |
| @opindex fno-common |
| In C code, controls the placement of uninitialized global variables. |
| Unix C compilers have traditionally permitted multiple definitions of |
| such variables in different compilation units by placing the variables |
| in a common block. |
| This is the behavior specified by @option{-fcommon}, and is the default |
| for GCC on most targets. |
| On the other hand, this behavior is not required by ISO C, and on some |
| targets may carry a speed or code size penalty on variable references. |
| The @option{-fno-common} option specifies that the compiler should place |
| uninitialized global variables in the data section of the object file, |
| rather than generating them as common blocks. |
| This has the effect that if the same variable is declared |
| (without @code{extern}) in two different compilations, |
| you get a multiple-definition error when you link them. |
| In this case, you must compile with @option{-fcommon} instead. |
| Compiling with @option{-fno-common} is useful on targets for which |
| it provides better performance, or if you wish to verify that the |
| program will work on other systems that always treat uninitialized |
| variable declarations this way. |
| |
| @item -fno-ident |
| @opindex fno-ident |
| Ignore the @samp{#ident} directive. |
| |
| @item -finhibit-size-directive |
| @opindex finhibit-size-directive |
| Don't output a @code{.size} assembler directive, or anything else that |
| would cause trouble if the function is split in the middle, and the |
| two halves are placed at locations far apart in memory. This option is |
| used when compiling @file{crtstuff.c}; you should not need to use it |
| for anything else. |
| |
| @item -fverbose-asm |
| @opindex fverbose-asm |
| Put extra commentary information in the generated assembly code to |
| make it more readable. This option is generally only of use to those |
| who actually need to read the generated assembly code (perhaps while |
| debugging the compiler itself). |
| |
| @option{-fno-verbose-asm}, the default, causes the |
| extra information to be omitted and is useful when comparing two assembler |
| files. |
| |
| @item -frecord-gcc-switches |
| @opindex frecord-gcc-switches |
| This switch causes the command line used to invoke the |
| compiler to be recorded into the object file that is being created. |
| This switch is only implemented on some targets and the exact format |
| of the recording is target and binary file format dependent, but it |
| usually takes the form of a section containing ASCII text. This |
| switch is related to the @option{-fverbose-asm} switch, but that |
| switch only records information in the assembler output file as |
| comments, so it never reaches the object file. |
| See also @option{-grecord-gcc-switches} for another |
| way of storing compiler options into the object file. |
| |
| @item -fpic |
| @opindex fpic |
| @cindex global offset table |
| @cindex PIC |
| Generate position-independent code (PIC) suitable for use in a shared |
| library, if supported for the target machine. Such code accesses all |
| constant addresses through a global offset table (GOT)@. The dynamic |
| loader resolves the GOT entries when the program starts (the dynamic |
| loader is not part of GCC; it is part of the operating system). If |
| the GOT size for the linked executable exceeds a machine-specific |
| maximum size, you get an error message from the linker indicating that |
| @option{-fpic} does not work; in that case, recompile with @option{-fPIC} |
| instead. (These maximums are 8k on the SPARC and 32k |
| on the m68k and RS/6000. The 386 has no such limit.) |
| |
| Position-independent code requires special support, and therefore works |
| only on certain machines. For the 386, GCC supports PIC for System V |
| but not for the Sun 386i. Code generated for the IBM RS/6000 is always |
| position-independent. |
| |
| When this flag is set, the macros @code{__pic__} and @code{__PIC__} |
| are defined to 1. |
| |
| @item -fPIC |
| @opindex fPIC |
| If supported for the target machine, emit position-independent code, |
| suitable for dynamic linking and avoiding any limit on the size of the |
| global offset table. This option makes a difference on the m68k, |
| PowerPC and SPARC@. |
| |
| Position-independent code requires special support, and therefore works |
| only on certain machines. |
| |
| When this flag is set, the macros @code{__pic__} and @code{__PIC__} |
| are defined to 2. |
| |
| @item -fpie |
| @itemx -fPIE |
| @opindex fpie |
| @opindex fPIE |
| These options are similar to @option{-fpic} and @option{-fPIC}, but |
| generated position independent code can be only linked into executables. |
| Usually these options are used when @option{-pie} GCC option is |
| used during linking. |
| |
| @option{-fpie} and @option{-fPIE} both define the macros |
| @code{__pie__} and @code{__PIE__}. The macros have the value 1 |
| for @option{-fpie} and 2 for @option{-fPIE}. |
| |
| @item -fno-jump-tables |
| @opindex fno-jump-tables |
| Do not use jump tables for switch statements even where it would be |
| more efficient than other code generation strategies. This option is |
| of use in conjunction with @option{-fpic} or @option{-fPIC} for |
| building code that forms part of a dynamic linker and cannot |
| reference the address of a jump table. On some targets, jump tables |
| do not require a GOT and this option is not needed. |
| |
| @item -ffixed-@var{reg} |
| @opindex ffixed |
| Treat the register named @var{reg} as a fixed register; generated code |
| should never refer to it (except perhaps as a stack pointer, frame |
| pointer or in some other fixed role). |
| |
| @var{reg} must be the name of a register. The register names accepted |
| are machine-specific and are defined in the @code{REGISTER_NAMES} |
| macro in the machine description macro file. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fcall-used-@var{reg} |
| @opindex fcall-used |
| Treat the register named @var{reg} as an allocable register that is |
| clobbered by function calls. It may be allocated for temporaries or |
| variables that do not live across a call. Functions compiled this way |
| do not save and restore the register @var{reg}. |
| |
| It is an error to use this flag with the frame pointer or stack pointer. |
| Use of this flag for other registers that have fixed pervasive roles in |
| the machine's execution model produces disastrous results. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fcall-saved-@var{reg} |
| @opindex fcall-saved |
| Treat the register named @var{reg} as an allocable register saved by |
| functions. It may be allocated even for temporaries or variables that |
| live across a call. Functions compiled this way save and restore |
| the register @var{reg} if they use it. |
| |
| It is an error to use this flag with the frame pointer or stack pointer. |
| Use of this flag for other registers that have fixed pervasive roles in |
| the machine's execution model produces disastrous results. |
| |
| A different sort of disaster results from the use of this flag for |
| a register in which function values may be returned. |
| |
| This flag does not have a negative form, because it specifies a |
| three-way choice. |
| |
| @item -fpack-struct[=@var{n}] |
| @opindex fpack-struct |
| Without a value specified, pack all structure members together without |
| holes. When a value is specified (which must be a small power of two), pack |
| structure members according to this value, representing the maximum |
| alignment (that is, objects with default alignment requirements larger than |
| this are output potentially unaligned at the next fitting location. |
| |
| @strong{Warning:} the @option{-fpack-struct} switch causes GCC to generate |
| code that is not binary compatible with code generated without that switch. |
| Additionally, it makes the code suboptimal. |
| Use it to conform to a non-default application binary interface. |
| |
| @item -finstrument-functions |
| @opindex finstrument-functions |
| Generate instrumentation calls for entry and exit to functions. Just |
| after function entry and just before function exit, the following |
| profiling functions are called with the address of the current |
| function and its call site. (On some platforms, |
| @code{__builtin_return_address} does not work beyond the current |
| function, so the call site information may not be available to the |
| profiling functions otherwise.) |
| |
| @smallexample |
| void __cyg_profile_func_enter (void *this_fn, |
| void *call_site); |
| void __cyg_profile_func_exit (void *this_fn, |
| void *call_site); |
| @end smallexample |
| |
| The first argument is the address of the start of the current function, |
| which may be looked up exactly in the symbol table. |
| |
| This instrumentation is also done for functions expanded inline in other |
| functions. The profiling calls indicate where, conceptually, the |
| inline function is entered and exited. This means that addressable |
| versions of such functions must be available. If all your uses of a |
| function are expanded inline, this may mean an additional expansion of |
| code size. If you use @samp{extern inline} in your C code, an |
| addressable version of such functions must be provided. (This is |
| normally the case anyway, but if you get lucky and the optimizer always |
| expands the functions inline, you might have gotten away without |
| providing static copies.) |
| |
| A function may be given the attribute @code{no_instrument_function}, in |
| which case this instrumentation is not done. This can be used, for |
| example, for the profiling functions listed above, high-priority |
| interrupt routines, and any functions from which the profiling functions |
| cannot safely be called (perhaps signal handlers, if the profiling |
| routines generate output or allocate memory). |
| |
| @item -finstrument-functions-exclude-file-list=@var{file},@var{file},@dots{} |
| @opindex finstrument-functions-exclude-file-list |
| |
| Set the list of functions that are excluded from instrumentation (see |
| the description of @code{-finstrument-functions}). If the file that |
| contains a function definition matches with one of @var{file}, then |
| that function is not instrumented. The match is done on substrings: |
| if the @var{file} parameter is a substring of the file name, it is |
| considered to be a match. |
| |
| For example: |
| |
| @smallexample |
| -finstrument-functions-exclude-file-list=/bits/stl,include/sys |
| @end smallexample |
| |
| @noindent |
| excludes any inline function defined in files whose pathnames |
| contain @code{/bits/stl} or @code{include/sys}. |
| |
| If, for some reason, you want to include letter @code{','} in one of |
| @var{sym}, write @code{'\,'}. For example, |
| @code{-finstrument-functions-exclude-file-list='\,\,tmp'} |
| (note the single quote surrounding the option). |
| |
| @item -finstrument-functions-exclude-function-list=@var{sym},@var{sym},@dots{} |
| @opindex finstrument-functions-exclude-function-list |
| |
| This is similar to @code{-finstrument-functions-exclude-file-list}, |
| but this option sets the list of function names to be excluded from |
| instrumentation. The function name to be matched is its user-visible |
| name, such as @code{vector<int> blah(const vector<int> &)}, not the |
| internal mangled name (e.g., @code{_Z4blahRSt6vectorIiSaIiEE}). The |
| match is done on substrings: if the @var{sym} parameter is a substring |
| of the function name, it is considered to be a match. For C99 and C++ |
| extended identifiers, the function name must be given in UTF-8, not |
| using universal character names. |
| |
| @item -fstack-check |
| @opindex fstack-check |
| Generate code to verify that you do not go beyond the boundary of the |
| stack. You should specify this flag if you are running in an |
| environment with multiple threads, but you only rarely need to specify it in |
| a single-threaded environment since stack overflow is automatically |
| detected on nearly all systems if there is only one stack. |
| |
| Note that this switch does not actually cause checking to be done; the |
| operating system or the language runtime must do that. The switch causes |
| generation of code to ensure that they see the stack being extended. |
| |
| You can additionally specify a string parameter: @code{no} means no |
| checking, @code{generic} means force the use of old-style checking, |
| @code{specific} means use the best checking method and is equivalent |
| to bare @option{-fstack-check}. |
| |
| Old-style checking is a generic mechanism that requires no specific |
| target support in the compiler but comes with the following drawbacks: |
| |
| @enumerate |
| @item |
| Modified allocation strategy for large objects: they are always |
| allocated dynamically if their size exceeds a fixed threshold. |
| |
| @item |
| Fixed limit on the size of the static frame of functions: when it is |
| topped by a particular function, stack checking is not reliable and |
| a warning is issued by the compiler. |
| |
| @item |
| Inefficiency: because of both the modified allocation strategy and the |
| generic implementation, code performance is hampered. |
| @end enumerate |
| |
| Note that old-style stack checking is also the fallback method for |
| @code{specific} if no target support has been added in the compiler. |
| |
| @item -fstack-limit-register=@var{reg} |
| @itemx -fstack-limit-symbol=@var{sym} |
| @itemx -fno-stack-limit |
| @opindex fstack-limit-register |
| @opindex fstack-limit-symbol |
| @opindex fno-stack-limit |
| Generate code to ensure that the stack does not grow beyond a certain value, |
| either the value of a register or the address of a symbol. If a larger |
| stack is required, a signal is raised at run time. For most targets, |
| the signal is raised before the stack overruns the boundary, so |
| it is possible to catch the signal without taking special precautions. |
| |
| For instance, if the stack starts at absolute address @samp{0x80000000} |
| and grows downwards, you can use the flags |
| @option{-fstack-limit-symbol=__stack_limit} and |
| @option{-Wl,--defsym,__stack_limit=0x7ffe0000} to enforce a stack limit |
| of 128KB@. Note that this may only work with the GNU linker. |
| |
| @item -fsplit-stack |
| @opindex fsplit-stack |
| Generate code to automatically split the stack before it overflows. |
| The resulting program has a discontiguous stack which can only |
| overflow if the program is unable to allocate any more memory. This |
| is most useful when running threaded programs, as it is no longer |
| necessary to calculate a good stack size to use for each thread. This |
| is currently only implemented for the i386 and x86_64 back ends running |
| GNU/Linux. |
| |
| When code compiled with @option{-fsplit-stack} calls code compiled |
| without @option{-fsplit-stack}, there may not be much stack space |
| available for the latter code to run. If compiling all code, |
| including library code, with @option{-fsplit-stack} is not an option, |
| then the linker can fix up these calls so that the code compiled |
| without @option{-fsplit-stack} always has a large stack. Support for |
| this is implemented in the gold linker in GNU binutils release 2.21 |
| and later. |
| |
| @item -fleading-underscore |
| @opindex fleading-underscore |
| This option and its counterpart, @option{-fno-leading-underscore}, forcibly |
| change the way C symbols are represented in the object file. One use |
| is to help link with legacy assembly code. |
| |
| @strong{Warning:} the @option{-fleading-underscore} switch causes GCC to |
| generate code that is not binary compatible with code generated without that |
| switch. Use it to conform to a non-default application binary interface. |
| Not all targets provide complete support for this switch. |
| |
| @item -ftls-model=@var{model} |
| @opindex ftls-model |
| Alter the thread-local storage model to be used (@pxref{Thread-Local}). |
| The @var{model} argument should be one of @code{global-dynamic}, |
| @code{local-dynamic}, @code{initial-exec} or @code{local-exec}. |
| |
| The default without @option{-fpic} is @code{initial-exec}; with |
| @option{-fpic} the default is @code{global-dynamic}. |
| |
| @item -fvisibility=@var{default|internal|hidden|protected} |
| @opindex fvisibility |
| Set the default ELF image symbol visibility to the specified option---all |
| symbols are marked with this unless overridden within the code. |
| Using this feature can very substantially improve linking and |
| load times of shared object libraries, produce more optimized |
| code, provide near-perfect API export and prevent symbol clashes. |
| It is @strong{strongly} recommended that you use this in any shared objects |
| you distribute. |
| |
| Despite the nomenclature, @code{default} always means public; i.e., |
| available to be linked against from outside the shared object. |
| @code{protected} and @code{internal} are pretty useless in real-world |
| usage so the only other commonly used option is @code{hidden}. |
| The default if @option{-fvisibility} isn't specified is |
| @code{default}, i.e., make every |
| symbol public---this causes the same behavior as previous versions of |
| GCC@. |
| |
| A good explanation of the benefits offered by ensuring ELF |
| symbols have the correct visibility is given by ``How To Write |
| Shared Libraries'' by Ulrich Drepper (which can be found at |
| @w{@uref{http://people.redhat.com/~drepper/}})---however a superior |
| solution made possible by this option to marking things hidden when |
| the default is public is to make the default hidden and mark things |
| public. This is the norm with DLLs on Windows and with @option{-fvisibility=hidden} |
| and @code{__attribute__ ((visibility("default")))} instead of |
| @code{__declspec(dllexport)} you get almost identical semantics with |
| identical syntax. This is a great boon to those working with |
| cross-platform projects. |
| |
| For those adding visibility support to existing code, you may find |
| @samp{#pragma GCC visibility} of use. This works by you enclosing |
| the declarations you wish to set visibility for with (for example) |
| @samp{#pragma GCC visibility push(hidden)} and |
| @samp{#pragma GCC visibility pop}. |
| Bear in mind that symbol visibility should be viewed @strong{as |
| part of the API interface contract} and thus all new code should |
| always specify visibility when it is not the default; i.e., declarations |
| only for use within the local DSO should @strong{always} be marked explicitly |
| as hidden as so to avoid PLT indirection overheads---making this |
| abundantly clear also aids readability and self-documentation of the code. |
| Note that due to ISO C++ specification requirements, @code{operator new} and |
| @code{operator delete} must always be of default visibility. |
| |
| Be aware that headers from outside your project, in particular system |
| headers and headers from any other library you use, may not be |
| expecting to be compiled with visibility other than the default. You |
| may need to explicitly say @samp{#pragma GCC visibility push(default)} |
| before including any such headers. |
| |
| @samp{extern} declarations are not affected by @option{-fvisibility}, so |
| a lot of code can be recompiled with @option{-fvisibility=hidden} with |
| no modifications. However, this means that calls to @code{extern} |
| functions with no explicit visibility use the PLT, so it is more |
| effective to use @code{__attribute ((visibility))} and/or |
| @code{#pragma GCC visibility} to tell the compiler which @code{extern} |
| declarations should be treated as hidden. |
| |
| Note that @option{-fvisibility} does affect C++ vague linkage |
| entities. This means that, for instance, an exception class that is |
| be thrown between DSOs must be explicitly marked with default |
| visibility so that the @samp{type_info} nodes are unified between |
| the DSOs. |
| |
| An overview of these techniques, their benefits and how to use them |
| is at @uref{http://gcc.gnu.org/@/wiki/@/Visibility}. |
| |
| @item -fstrict-volatile-bitfields |
| @opindex fstrict-volatile-bitfields |
| This option should be used if accesses to volatile bit-fields (or other |
| structure fields, although the compiler usually honors those types |
| anyway) should use a single access of the width of the |
| field's type, aligned to a natural alignment if possible. For |
| example, targets with memory-mapped peripheral registers might require |
| all such accesses to be 16 bits wide; with this flag you can |
| declare all peripheral bit-fields as @code{unsigned short} (assuming short |
| is 16 bits on these targets) to force GCC to use 16-bit accesses |
| instead of, perhaps, a more efficient 32-bit access. |
| |
| If this option is disabled, the compiler uses the most efficient |
| instruction. In the previous example, that might be a 32-bit load |
| instruction, even though that accesses bytes that do not contain |
| any portion of the bit-field, or memory-mapped registers unrelated to |
| the one being updated. |
| |
| If the target requires strict alignment, and honoring the field |
| type would require violating this alignment, a warning is issued. |
| If the field has @code{packed} attribute, the access is done without |
| honoring the field type. If the field doesn't have @code{packed} |
| attribute, the access is done honoring the field type. In both cases, |
| GCC assumes that the user knows something about the target hardware |
| that it is unaware of. |
| |
| The default value of this option is determined by the application binary |
| interface for the target processor. |
| |
| @item -fsync-libcalls |
| @opindex fsync-libcalls |
| This option controls whether any out-of-line instance of the @code{__sync} |
| family of functions may be used to implement the C++11 @code{__atomic} |
| family of functions. |
| |
| The default value of this option is enabled, thus the only useful form |
| of the option is @option{-fno-sync-libcalls}. This option is used in |
| the implementation of the @file{libatomic} runtime library. |
| |
| @end table |
| |
| @c man end |
| |
| @node Environment Variables |
| @section Environment Variables Affecting GCC |
| @cindex environment variables |
| |
| @c man begin ENVIRONMENT |
| This section describes several environment variables that affect how GCC |
| operates. Some of them work by specifying directories or prefixes to use |
| when searching for various kinds of files. Some are used to specify other |
| aspects of the compilation environment. |
| |
| Note that you can also specify places to search using options such as |
| @option{-B}, @option{-I} and @option{-L} (@pxref{Directory Options}). These |
| take precedence over places specified using environment variables, which |
| in turn take precedence over those specified by the configuration of GCC@. |
| @xref{Driver,, Controlling the Compilation Driver @file{gcc}, gccint, |
| GNU Compiler Collection (GCC) Internals}. |
| |
| @table @env |
| @item LANG |
| @itemx LC_CTYPE |
| @c @itemx LC_COLLATE |
| @itemx LC_MESSAGES |
| @c @itemx LC_MONETARY |
| @c @itemx LC_NUMERIC |
| @c @itemx LC_TIME |
| @itemx LC_ALL |
| @findex LANG |
| @findex LC_CTYPE |
| @c @findex LC_COLLATE |
| @findex LC_MESSAGES |
| @c @findex LC_MONETARY |
| @c @findex LC_NUMERIC |
| @c @findex LC_TIME |
| @findex LC_ALL |
| @cindex locale |
| These environment variables control the way that GCC uses |
| localization information which allows GCC to work with different |
| national conventions. GCC inspects the locale categories |
| @env{LC_CTYPE} and @env{LC_MESSAGES} if it has been configured to do |
| so. These locale categories can be set to any value supported by your |
| installation. A typical value is @samp{en_GB.UTF-8} for English in the United |
| Kingdom encoded in UTF-8. |
| |
| The @env{LC_CTYPE} environment variable specifies character |
| classification. GCC uses it to determine the character boundaries in |
| a string; this is needed for some multibyte encodings that contain quote |
| and escape characters that are otherwise interpreted as a string |
| end or escape. |
| |
| The @env{LC_MESSAGES} environment variable specifies the language to |
| use in diagnostic messages. |
| |
| If the @env{LC_ALL} environment variable is set, it overrides the value |
| of @env{LC_CTYPE} and @env{LC_MESSAGES}; otherwise, @env{LC_CTYPE} |
| and @env{LC_MESSAGES} default to the value of the @env{LANG} |
| environment variable. If none of these variables are set, GCC |
| defaults to traditional C English behavior. |
| |
| @item TMPDIR |
| @findex TMPDIR |
| If @env{TMPDIR} is set, it specifies the directory to use for temporary |
| files. GCC uses temporary files to hold the output of one stage of |
| compilation which is to be used as input to the next stage: for example, |
| the output of the preprocessor, which is the input to the compiler |
| proper. |
| |
| @item GCC_COMPARE_DEBUG |
| @findex GCC_COMPARE_DEBUG |
| Setting @env{GCC_COMPARE_DEBUG} is nearly equivalent to passing |
| @option{-fcompare-debug} to the compiler driver. See the documentation |
| of this option for more details. |
| |
| @item GCC_EXEC_PREFIX |
| @findex GCC_EXEC_PREFIX |
| If @env{GCC_EXEC_PREFIX} is set, it specifies a prefix to use in the |
| names of the subprograms executed by the compiler. No slash is added |
| when this prefix is combined with the name of a subprogram, but you can |
| specify a prefix that ends with a slash if you wish. |
| |
| If @env{GCC_EXEC_PREFIX} is not set, GCC attempts to figure out |
| an appropriate prefix to use based on the pathname it is invoked with. |
| |
| If GCC cannot find the subprogram using the specified prefix, it |
| tries looking in the usual places for the subprogram. |
| |
| The default value of @env{GCC_EXEC_PREFIX} is |
| @file{@var{prefix}/lib/gcc/} where @var{prefix} is the prefix to |
| the installed compiler. In many cases @var{prefix} is the value |
| of @code{prefix} when you ran the @file{configure} script. |
| |
| Other prefixes specified with @option{-B} take precedence over this prefix. |
| |
| This prefix is also used for finding files such as @file{crt0.o} that are |
| used for linking. |
| |
| In addition, the prefix is used in an unusual way in finding the |
| directories to search for header files. For each of the standard |
| directories whose name normally begins with @samp{/usr/local/lib/gcc} |
| (more precisely, with the value of @env{GCC_INCLUDE_DIR}), GCC tries |
| replacing that beginning with the specified prefix to produce an |
| alternate directory name. Thus, with @option{-Bfoo/}, GCC searches |
| @file{foo/bar} just before it searches the standard directory |
| @file{/usr/local/lib/bar}. |
| If a standard directory begins with the configured |
| @var{prefix} then the value of @var{prefix} is replaced by |
| @env{GCC_EXEC_PREFIX} when looking for header files. |
| |
| @item COMPILER_PATH |
| @findex COMPILER_PATH |
| The value of @env{COMPILER_PATH} is a colon-separated list of |
| directories, much like @env{PATH}. GCC tries the directories thus |
| specified when searching for subprograms, if it can't find the |
| subprograms using @env{GCC_EXEC_PREFIX}. |
| |
| @item LIBRARY_PATH |
| @findex LIBRARY_PATH |
| The value of @env{LIBRARY_PATH} is a colon-separated list of |
| directories, much like @env{PATH}. When configured as a native compiler, |
| GCC tries the directories thus specified when searching for special |
| linker files, if it can't find them using @env{GCC_EXEC_PREFIX}. Linking |
| using GCC also uses these directories when searching for ordinary |
| libraries for the @option{-l} option (but directories specified with |
| @option{-L} come first). |
| |
| @item LANG |
| @findex LANG |
| @cindex locale definition |
| This variable is used to pass locale information to the compiler. One way in |
| which this information is used is to determine the character set to be used |
| when character literals, string literals and comments are parsed in C and C++. |
| When the compiler is configured to allow multibyte characters, |
| the following values for @env{LANG} are recognized: |
| |
| @table @samp |
| @item C-JIS |
| Recognize JIS characters. |
| @item C-SJIS |
| Recognize SJIS characters. |
| @item C-EUCJP |
| Recognize EUCJP characters. |
| @end table |
| |
| If @env{LANG} is not defined, or if it has some other value, then the |
| compiler uses @code{mblen} and @code{mbtowc} as defined by the default locale to |
| recognize and translate multibyte characters. |
| @end table |
| |
| @noindent |
| Some additional environment variables affect the behavior of the |
| preprocessor. |
| |
| @include cppenv.texi |
| |
| @c man end |
| |
| @node Precompiled Headers |
| @section Using Precompiled Headers |
| @cindex precompiled headers |
| @cindex speed of compilation |
| |
| Often large projects have many header files that are included in every |
| source file. The time the compiler takes to process these header files |
| over and over again can account for nearly all of the time required to |
| build the project. To make builds faster, GCC allows you to |
| @dfn{precompile} a header file. |
| |
| To create a precompiled header file, simply compile it as you would any |
| other file, if necessary using the @option{-x} option to make the driver |
| treat it as a C or C++ header file. You may want to use a |
| tool like @command{make} to keep the precompiled header up-to-date when |
| the headers it contains change. |
| |
| A precompiled header file is searched for when @code{#include} is |
| seen in the compilation. As it searches for the included file |
| (@pxref{Search Path,,Search Path,cpp,The C Preprocessor}) the |
| compiler looks for a precompiled header in each directory just before it |
| looks for the include file in that directory. The name searched for is |
| the name specified in the @code{#include} with @samp{.gch} appended. If |
| the precompiled header file can't be used, it is ignored. |
| |
| For instance, if you have @code{#include "all.h"}, and you have |
| @file{all.h.gch} in the same directory as @file{all.h}, then the |
| precompiled header file is used if possible, and the original |
| header is used otherwise. |
| |
| Alternatively, you might decide to put the precompiled header file in a |
| directory and use @option{-I} to ensure that directory is searched |
| before (or instead of) the directory containing the original header. |
| Then, if you want to check that the precompiled header file is always |
| used, you can put a file of the same name as the original header in this |
| directory containing an @code{#error} command. |
| |
| This also works with @option{-include}. So yet another way to use |
| precompiled headers, good for projects not designed with precompiled |
| header files in mind, is to simply take most of the header files used by |
| a project, include them from another header file, precompile that header |
| file, and @option{-include} the precompiled header. If the header files |
| have guards against multiple inclusion, they are skipped because |
| they've already been included (in the precompiled header). |
| |
| If you need to precompile the same header file for different |
| languages, targets, or compiler options, you can instead make a |
| @emph{directory} named like @file{all.h.gch}, and put each precompiled |
| header in the directory, perhaps using @option{-o}. It doesn't matter |
| what you call the files in the directory; every precompiled header in |
| the directory is considered. The first precompiled header |
| encountered in the directory that is valid for this compilation is |
| used; they're searched in no particular order. |
| |
| There are many other possibilities, limited only by your imagination, |
| good sense, and the constraints of your build system. |
| |
| A precompiled header file can be used only when these conditions apply: |
| |
| @itemize |
| @item |
| Only one precompiled header can be used in a particular compilation. |
| |
| @item |
| A precompiled header can't be used once the first C token is seen. You |
| can have preprocessor directives before a precompiled header; you cannot |
| include a precompiled header from inside another header. |
| |
| @item |
| The precompiled header file must be produced for the same language as |
| the current compilation. You can't use a C precompiled header for a C++ |
| compilation. |
| |
| @item |
| The precompiled header file must have been produced by the same compiler |
| binary as the current compilation is using. |
| |
| @item |
| Any macros defined before the precompiled header is included must |
| either be defined in the same way as when the precompiled header was |
| generated, or must not affect the precompiled header, which usually |
| means that they don't appear in the precompiled header at all. |
| |
| The @option{-D} option is one way to define a macro before a |
| precompiled header is included; using a @code{#define} can also do it. |
| There are also some options that define macros implicitly, like |
| @option{-O} and @option{-Wdeprecated}; the same rule applies to macros |
| defined this way. |
| |
| @item If debugging information is output when using the precompiled |
| header, using @option{-g} or similar, the same kind of debugging information |
| must have been output when building the precompiled header. However, |
| a precompiled header built using @option{-g} can be used in a compilation |
| when no debugging information is being output. |
| |
| @item The same @option{-m} options must generally be used when building |
| and using the precompiled header. @xref{Submodel Options}, |
| for any cases where this rule is relaxed. |
| |
| @item Each of the following options must be the same when building and using |
| the precompiled header: |
| |
| @gccoptlist{-fexceptions} |
| |
| @item |
| Some other command-line options starting with @option{-f}, |
| @option{-p}, or @option{-O} must be defined in the same way as when |
| the precompiled header was generated. At present, it's not clear |
| which options are safe to change and which are not; the safest choice |
| is to use exactly the same options when generating and using the |
| precompiled header. The following are known to be safe: |
| |
| @gccoptlist{-fmessage-length= -fpreprocessed -fsched-interblock @gol |
| -fsched-spec -fsched-spec-load -fsched-spec-load-dangerous @gol |
| -fsched-verbose=@var{number} -fschedule-insns -fvisibility= @gol |
| -pedantic-errors} |
| |
| @end itemize |
| |
| For all of these except the last, the compiler automatically |
| ignores the precompiled header if the conditions aren't met. If you |
| find an option combination that doesn't work and doesn't cause the |
| precompiled header to be ignored, please consider filing a bug report, |
| see @ref{Bugs}. |
| |
| If you do use differing options when generating and using the |
| precompiled header, the actual behavior is a mixture of the |
| behavior for the options. For instance, if you use @option{-g} to |
| generate the precompiled header but not when using it, you may or may |
| not get debugging information for routines in the precompiled header. |