Stephen Hines | c6ca60f | 2023-05-09 02:19:22 -0700 | [diff] [blame^] | 1 | //===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- 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 file implements the AntiDepBreaker class, which implements |
| 10 | // anti-dependence breaking heuristics for post-register-allocation scheduling. |
| 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
| 14 | #ifndef LLVM_CODEGEN_ANTIDEPBREAKER_H |
| 15 | #define LLVM_CODEGEN_ANTIDEPBREAKER_H |
| 16 | |
| 17 | #include "llvm/ADT/iterator_range.h" |
| 18 | #include "llvm/CodeGen/MachineBasicBlock.h" |
| 19 | #include "llvm/CodeGen/MachineInstr.h" |
| 20 | #include "llvm/CodeGen/TargetSubtargetInfo.h" |
| 21 | #include "llvm/Support/Compiler.h" |
| 22 | #include <cassert> |
| 23 | #include <utility> |
| 24 | #include <vector> |
| 25 | |
| 26 | namespace llvm { |
| 27 | |
| 28 | class RegisterClassInfo; |
| 29 | |
| 30 | /// This class works in conjunction with the post-RA scheduler to rename |
| 31 | /// registers to break register anti-dependencies (WAR hazards). |
| 32 | class AntiDepBreaker { |
| 33 | public: |
| 34 | using DbgValueVector = |
| 35 | std::vector<std::pair<MachineInstr *, MachineInstr *>>; |
| 36 | |
| 37 | virtual ~AntiDepBreaker(); |
| 38 | |
| 39 | /// Initialize anti-dep breaking for a new basic block. |
| 40 | virtual void StartBlock(MachineBasicBlock *BB) = 0; |
| 41 | |
| 42 | /// Identifiy anti-dependencies within a basic-block region and break them by |
| 43 | /// renaming registers. Return the number of anti-dependencies broken. |
| 44 | virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits, |
| 45 | MachineBasicBlock::iterator Begin, |
| 46 | MachineBasicBlock::iterator End, |
| 47 | unsigned InsertPosIndex, |
| 48 | DbgValueVector &DbgValues) = 0; |
| 49 | |
| 50 | /// Update liveness information to account for the current |
| 51 | /// instruction, which will not be scheduled. |
| 52 | virtual void Observe(MachineInstr &MI, unsigned Count, |
| 53 | unsigned InsertPosIndex) = 0; |
| 54 | |
| 55 | /// Finish anti-dep breaking for a basic block. |
| 56 | virtual void FinishBlock() = 0; |
| 57 | |
| 58 | /// Update DBG_VALUE or DBG_PHI if dependency breaker is updating |
| 59 | /// other machine instruction to use NewReg. |
| 60 | void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) { |
| 61 | if (MI.isDebugValue()) { |
| 62 | if (MI.getDebugOperand(0).isReg() && |
| 63 | MI.getDebugOperand(0).getReg() == OldReg) |
| 64 | MI.getDebugOperand(0).setReg(NewReg); |
| 65 | } else if (MI.isDebugPHI()) { |
| 66 | if (MI.getOperand(0).isReg() && |
| 67 | MI.getOperand(0).getReg() == OldReg) |
| 68 | MI.getOperand(0).setReg(NewReg); |
| 69 | } else { |
| 70 | llvm_unreachable("MI is not DBG_VALUE / DBG_PHI!"); |
| 71 | } |
| 72 | } |
| 73 | |
| 74 | /// Update all DBG_VALUE instructions that may be affected by the dependency |
| 75 | /// breaker's update of ParentMI to use NewReg. |
| 76 | void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI, |
| 77 | unsigned OldReg, unsigned NewReg) { |
| 78 | // The following code is dependent on the order in which the DbgValues are |
| 79 | // constructed in ScheduleDAGInstrs::buildSchedGraph. |
| 80 | MachineInstr *PrevDbgMI = nullptr; |
| 81 | for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) { |
| 82 | MachineInstr *PrevMI = DV.second; |
| 83 | if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) { |
| 84 | MachineInstr *DbgMI = DV.first; |
| 85 | UpdateDbgValue(*DbgMI, OldReg, NewReg); |
| 86 | PrevDbgMI = DbgMI; |
| 87 | } else if (PrevDbgMI) { |
| 88 | break; // If no match and already found a DBG_VALUE, we're done. |
| 89 | } |
| 90 | } |
| 91 | } |
| 92 | }; |
| 93 | |
| 94 | AntiDepBreaker *createAggressiveAntiDepBreaker( |
| 95 | MachineFunction &MFi, const RegisterClassInfo &RCI, |
| 96 | TargetSubtargetInfo::RegClassVector &CriticalPathRCs); |
| 97 | |
| 98 | AntiDepBreaker *createCriticalAntiDepBreaker(MachineFunction &MFi, |
| 99 | const RegisterClassInfo &RCI); |
| 100 | |
| 101 | } // end namespace llvm |
| 102 | |
| 103 | #endif // LLVM_CODEGEN_ANTIDEPBREAKER_H |