Yi Kong | 878f994 | 2023-12-13 12:55:04 +0900 | [diff] [blame^] | 1 | //===- LazyBranchProbabilityInfo.h - Lazy Branch Probability ----*- C++ -*-===// |
| 2 | // |
| 3 | // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| 4 | // See https://llvm.org/LICENSE.txt for license information. |
| 5 | // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| 6 | // |
| 7 | //===----------------------------------------------------------------------===// |
| 8 | // |
| 9 | // This is an alternative analysis pass to BranchProbabilityInfoWrapperPass. |
| 10 | // The difference is that with this pass the branch probabilities are not |
| 11 | // computed when the analysis pass is executed but rather when the BPI results |
| 12 | // is explicitly requested by the analysis client. |
| 13 | // |
| 14 | //===----------------------------------------------------------------------===// |
| 15 | |
| 16 | #ifndef LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
| 17 | #define LLVM_ANALYSIS_LAZYBRANCHPROBABILITYINFO_H |
| 18 | |
| 19 | #include "llvm/Analysis/BranchProbabilityInfo.h" |
| 20 | #include "llvm/Pass.h" |
| 21 | |
| 22 | namespace llvm { |
| 23 | class AnalysisUsage; |
| 24 | class Function; |
| 25 | class LoopInfo; |
| 26 | class TargetLibraryInfo; |
| 27 | |
| 28 | /// This is an alternative analysis pass to |
| 29 | /// BranchProbabilityInfoWrapperPass. The difference is that with this pass the |
| 30 | /// branch probabilities are not computed when the analysis pass is executed but |
| 31 | /// rather when the BPI results is explicitly requested by the analysis client. |
| 32 | /// |
| 33 | /// There are some additional requirements for any client pass that wants to use |
| 34 | /// the analysis: |
| 35 | /// |
| 36 | /// 1. The pass needs to initialize dependent passes with: |
| 37 | /// |
| 38 | /// INITIALIZE_PASS_DEPENDENCY(LazyBPIPass) |
| 39 | /// |
| 40 | /// 2. Similarly, getAnalysisUsage should call: |
| 41 | /// |
| 42 | /// LazyBranchProbabilityInfoPass::getLazyBPIAnalysisUsage(AU) |
| 43 | /// |
| 44 | /// 3. The computed BPI should be requested with |
| 45 | /// getAnalysis<LazyBranchProbabilityInfoPass>().getBPI() before LoopInfo |
| 46 | /// could be invalidated for example by changing the CFG. |
| 47 | /// |
| 48 | /// Note that it is expected that we wouldn't need this functionality for the |
| 49 | /// new PM since with the new PM, analyses are executed on demand. |
| 50 | class LazyBranchProbabilityInfoPass : public FunctionPass { |
| 51 | |
| 52 | /// Wraps a BPI to allow lazy computation of the branch probabilities. |
| 53 | /// |
| 54 | /// A pass that only conditionally uses BPI can uncondtionally require the |
| 55 | /// analysis without paying for the overhead if BPI doesn't end up being used. |
| 56 | class LazyBranchProbabilityInfo { |
| 57 | public: |
| 58 | LazyBranchProbabilityInfo(const Function *F, const LoopInfo *LI, |
| 59 | const TargetLibraryInfo *TLI) |
| 60 | : F(F), LI(LI), TLI(TLI) {} |
| 61 | |
| 62 | /// Retrieve the BPI with the branch probabilities computed. |
| 63 | BranchProbabilityInfo &getCalculated() { |
| 64 | if (!Calculated) { |
| 65 | assert(F && LI && "call setAnalysis"); |
| 66 | BPI.calculate(*F, *LI, TLI, nullptr, nullptr); |
| 67 | Calculated = true; |
| 68 | } |
| 69 | return BPI; |
| 70 | } |
| 71 | |
| 72 | const BranchProbabilityInfo &getCalculated() const { |
| 73 | return const_cast<LazyBranchProbabilityInfo *>(this)->getCalculated(); |
| 74 | } |
| 75 | |
| 76 | private: |
| 77 | BranchProbabilityInfo BPI; |
| 78 | bool Calculated = false; |
| 79 | const Function *F; |
| 80 | const LoopInfo *LI; |
| 81 | const TargetLibraryInfo *TLI; |
| 82 | }; |
| 83 | |
| 84 | std::unique_ptr<LazyBranchProbabilityInfo> LBPI; |
| 85 | |
| 86 | public: |
| 87 | static char ID; |
| 88 | |
| 89 | LazyBranchProbabilityInfoPass(); |
| 90 | |
| 91 | /// Compute and return the branch probabilities. |
| 92 | BranchProbabilityInfo &getBPI() { return LBPI->getCalculated(); } |
| 93 | |
| 94 | /// Compute and return the branch probabilities. |
| 95 | const BranchProbabilityInfo &getBPI() const { return LBPI->getCalculated(); } |
| 96 | |
| 97 | void getAnalysisUsage(AnalysisUsage &AU) const override; |
| 98 | |
| 99 | /// Helper for client passes to set up the analysis usage on behalf of this |
| 100 | /// pass. |
| 101 | static void getLazyBPIAnalysisUsage(AnalysisUsage &AU); |
| 102 | |
| 103 | bool runOnFunction(Function &F) override; |
| 104 | void releaseMemory() override; |
| 105 | void print(raw_ostream &OS, const Module *M) const override; |
| 106 | }; |
| 107 | |
| 108 | /// Helper for client passes to initialize dependent passes for LBPI. |
| 109 | void initializeLazyBPIPassPass(PassRegistry &Registry); |
| 110 | |
| 111 | /// Simple trait class that provides a mapping between BPI passes and the |
| 112 | /// corresponding BPInfo. |
| 113 | template <typename PassT> struct BPIPassTrait { |
| 114 | static PassT &getBPI(PassT *P) { return *P; } |
| 115 | }; |
| 116 | |
| 117 | template <> struct BPIPassTrait<LazyBranchProbabilityInfoPass> { |
| 118 | static BranchProbabilityInfo &getBPI(LazyBranchProbabilityInfoPass *P) { |
| 119 | return P->getBPI(); |
| 120 | } |
| 121 | }; |
| 122 | } |
| 123 | #endif |