1 //===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- C++ -*-===//
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
7 //===----------------------------------------------------------------------===//
9 // This file implements the AntiDepBreaker class, which implements
10 // anti-dependence breaking heuristics for post-register-allocation scheduling.
12 //===----------------------------------------------------------------------===//
14 #ifndef LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
15 #define LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H
17 #include "llvm/ADT/iterator_range.h"
18 #include "llvm/CodeGen/MachineBasicBlock.h"
19 #include "llvm/CodeGen/MachineInstr.h"
20 #include "llvm/CodeGen/ScheduleDAG.h"
21 #include "llvm/CodeGen/TargetSubtargetInfo.h"
22 #include "llvm/Support/Compiler.h"
29 class RegisterClassInfo;
31 /// This class works in conjunction with the post-RA scheduler to rename
32 /// registers to break register anti-dependencies (WAR hazards).
33 class AntiDepBreaker {
35 using DbgValueVector =
36 std::vector<std::pair<MachineInstr *, MachineInstr *>>;
38 virtual ~AntiDepBreaker();
40 /// Initialize anti-dep breaking for a new basic block.
41 virtual void StartBlock(MachineBasicBlock *BB) = 0;
43 /// Identifiy anti-dependencies within a basic-block region and break them by
44 /// renaming registers. Return the number of anti-dependencies broken.
45 virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
46 MachineBasicBlock::iterator Begin,
47 MachineBasicBlock::iterator End,
48 unsigned InsertPosIndex,
49 DbgValueVector &DbgValues) = 0;
51 /// Update liveness information to account for the current
52 /// instruction, which will not be scheduled.
53 virtual void Observe(MachineInstr &MI, unsigned Count,
54 unsigned InsertPosIndex) = 0;
56 /// Finish anti-dep breaking for a basic block.
57 virtual void FinishBlock() = 0;
59 /// Update DBG_VALUE if dependency breaker is updating
60 /// other machine instruction to use NewReg.
61 void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) {
62 assert(MI.isDebugValue() && "MI is not DBG_VALUE!");
63 if (MI.getDebugOperand(0).isReg() &&
64 MI.getDebugOperand(0).getReg() == OldReg)
65 MI.getDebugOperand(0).setReg(NewReg);
68 /// Update all DBG_VALUE instructions that may be affected by the dependency
69 /// breaker's update of ParentMI to use NewReg.
70 void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
71 unsigned OldReg, unsigned NewReg) {
72 // The following code is dependent on the order in which the DbgValues are
73 // constructed in ScheduleDAGInstrs::buildSchedGraph.
74 MachineInstr *PrevDbgMI = nullptr;
75 for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
76 MachineInstr *PrevMI = DV.second;
77 if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
78 MachineInstr *DbgMI = DV.first;
79 UpdateDbgValue(*DbgMI, OldReg, NewReg);
81 } else if (PrevDbgMI) {
82 break; // If no match and already found a DBG_VALUE, we're done.
88 AntiDepBreaker *createAggressiveAntiDepBreaker(
89 MachineFunction &MFi, const RegisterClassInfo &RCI,
90 TargetSubtargetInfo::RegClassVector &CriticalPathRCs);
92 AntiDepBreaker *createCriticalAntiDepBreaker(MachineFunction &MFi,
93 const RegisterClassInfo &RCI);
95 } // end namespace llvm
97 #endif // LLVM_LIB_CODEGEN_ANTIDEPBREAKER_H