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//===- llvm/CodeGen/AntiDepBreaker.h - Anti-Dependence Breaking -*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file implements the AntiDepBreaker class, which implements
// anti-dependence breaking heuristics for post-register-allocation scheduling.
#include "llvm/ADT/iterator_range.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Support/Compiler.h"
#include <cassert>
#include <utility>
#include <vector>
namespace llvm {
class RegisterClassInfo;
/// This class works in conjunction with the post-RA scheduler to rename
/// registers to break register anti-dependencies (WAR hazards).
class AntiDepBreaker {
using DbgValueVector =
std::vector<std::pair<MachineInstr *, MachineInstr *>>;
virtual ~AntiDepBreaker();
/// Initialize anti-dep breaking for a new basic block.
virtual void StartBlock(MachineBasicBlock *BB) = 0;
/// Identifiy anti-dependencies within a basic-block region and break them by
/// renaming registers. Return the number of anti-dependencies broken.
virtual unsigned BreakAntiDependencies(const std::vector<SUnit> &SUnits,
MachineBasicBlock::iterator Begin,
MachineBasicBlock::iterator End,
unsigned InsertPosIndex,
DbgValueVector &DbgValues) = 0;
/// Update liveness information to account for the current
/// instruction, which will not be scheduled.
virtual void Observe(MachineInstr &MI, unsigned Count,
unsigned InsertPosIndex) = 0;
/// Finish anti-dep breaking for a basic block.
virtual void FinishBlock() = 0;
/// Update DBG_VALUE or DBG_PHI if dependency breaker is updating
/// other machine instruction to use NewReg.
void UpdateDbgValue(MachineInstr &MI, unsigned OldReg, unsigned NewReg) {
if (MI.isDebugValue()) {
if (MI.getDebugOperand(0).isReg() &&
MI.getDebugOperand(0).getReg() == OldReg)
} else if (MI.isDebugPHI()) {
if (MI.getOperand(0).isReg() &&
MI.getOperand(0).getReg() == OldReg)
} else {
llvm_unreachable("MI is not DBG_VALUE / DBG_PHI!");
/// Update all DBG_VALUE instructions that may be affected by the dependency
/// breaker's update of ParentMI to use NewReg.
void UpdateDbgValues(const DbgValueVector &DbgValues, MachineInstr *ParentMI,
unsigned OldReg, unsigned NewReg) {
// The following code is dependent on the order in which the DbgValues are
// constructed in ScheduleDAGInstrs::buildSchedGraph.
MachineInstr *PrevDbgMI = nullptr;
for (const auto &DV : make_range(DbgValues.crbegin(), DbgValues.crend())) {
MachineInstr *PrevMI = DV.second;
if ((PrevMI == ParentMI) || (PrevMI == PrevDbgMI)) {
MachineInstr *DbgMI = DV.first;
UpdateDbgValue(*DbgMI, OldReg, NewReg);
PrevDbgMI = DbgMI;
} else if (PrevDbgMI) {
break; // If no match and already found a DBG_VALUE, we're done.
AntiDepBreaker *createAggressiveAntiDepBreaker(
MachineFunction &MFi, const RegisterClassInfo &RCI,
TargetSubtargetInfo::RegClassVector &CriticalPathRCs);
AntiDepBreaker *createCriticalAntiDepBreaker(MachineFunction &MFi,
const RegisterClassInfo &RCI);
} // end namespace llvm