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_LIB_CODEGEN_ANTIDEPBREAKER_H 15 #define LLVM_LIB_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/MachineOperand.h" 21 #include "llvm/CodeGen/ScheduleDAG.h" 22 #include "llvm/Support/Compiler.h" 23 #include <cassert> 24 #include <utility> 25 #include <vector> 26 27 namespace llvm { 28 29 /// This class works in conjunction with the post-RA scheduler to rename 30 /// registers to break register anti-dependencies (WAR hazards). 31 class LLVM_LIBRARY_VISIBILITY AntiDepBreaker { 32 public: 33 using DbgValueVector = 34 std::vector<std::pair<MachineInstr *, MachineInstr *>>; 35 36 virtual ~AntiDepBreaker(); 37 38 /// Initialize anti-dep breaking for a new basic block. 39 virtual void StartBlock(MachineBasicBlock *BB) = 0; 40 41 /// Identifiy anti-dependencies within a basic-block region and break them by 42 /// renaming registers. Return the number of anti-dependencies broken. 43 virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits, 44 MachineBasicBlock::iterator Begin, 45 MachineBasicBlock::iterator End, 46 unsigned InsertPosIndex, 47 DbgValueVector &DbgValues) = 0; 48 49 /// Update liveness information to account for the current 50 /// instruction, which will not be scheduled. 51 virtual void Observe(MachineInstr &MI, unsigned Count, 52 unsigned InsertPosIndex) = 0; 53 54 /// Finish anti-dep breaking for a basic block. 55 virtual void FinishBlock() = 0; 56 57 /// Update DBG_VALUE if dependency breaker is updating 58 /// other machine instruction to use NewReg. UpdateDbgValue(MachineInstr & MI,unsigned OldReg,unsigned NewReg)59 void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) { 60 assert(MI.isDebugValue() && "MI is not DBG_VALUE!"); 61 if (MI.getOperand(0).isReg() && MI.getOperand(0).getReg() == OldReg) 62 MI.getOperand(0).setReg(NewReg); 63 } 64 65 /// Update all DBG_VALUE instructions that may be affected by the dependency 66 /// breaker's update of ParentMI to use NewReg. UpdateDbgValues(const DbgValueVector & DbgValues,MachineInstr * ParentMI,unsigned OldReg,unsigned NewReg)67 void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI, 68 unsigned OldReg, unsigned NewReg) { 69 // The following code is dependent on the order in which the DbgValues are 70 // constructed in ScheduleDAGInstrs::buildSchedGraph. 71 MachineInstr *PrevDbgMI = nullptr; 72 for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) { 73 MachineInstr *PrevMI = DV.second; 74 if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) { 75 MachineInstr *DbgMI = DV.first; 76 UpdateDbgValue(*DbgMI, OldReg, NewReg); 77 PrevDbgMI = DbgMI; 78 } else if (PrevDbgMI) { 79 break; // If no match and already found a DBG_VALUE, we're done. 80 } 81 } 82 } 83 }; 84 85 } // end namespace llvm 86 87 #endif // LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H 88