114 lines · cpp
1//===----- PostRAHazardRecognizer.cpp - hazard recognizer -----------------===//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-exception6//7//===----------------------------------------------------------------------===//8//9/// \file10/// This runs the hazard recognizer and emits noops when necessary. This11/// gives targets a way to run the hazard recognizer without running one of12/// the schedulers. Example use cases for this pass would be:13///14/// - Targets that need the hazard recognizer to be run at -O0.15/// - Targets that want to guarantee that hazards at the beginning of16/// scheduling regions are handled correctly. The post-RA scheduler is17/// a top-down scheduler, but when there are multiple scheduling regions18/// in a basic block, it visits the regions in bottom-up order. This19/// makes it impossible for the scheduler to gauranttee it can correctly20/// handle hazards at the beginning of scheduling regions.21///22/// This pass traverses all the instructions in a program in top-down order.23/// In contrast to the instruction scheduling passes, this pass never resets24/// the hazard recognizer to ensure it can correctly handles noop hazards at25/// the beginning of blocks.26//27//===----------------------------------------------------------------------===//28 29#include "llvm/CodeGen/PostRAHazardRecognizer.h"30#include "llvm/ADT/Statistic.h"31#include "llvm/CodeGen/MachineFunctionPass.h"32#include "llvm/CodeGen/ScheduleHazardRecognizer.h"33#include "llvm/CodeGen/TargetInstrInfo.h"34#include "llvm/CodeGen/TargetSubtargetInfo.h"35#include "llvm/InitializePasses.h"36#include "llvm/Pass.h"37using namespace llvm;38 39#define DEBUG_TYPE "post-RA-hazard-rec"40 41STATISTIC(NumNoops, "Number of noops inserted");42 43namespace {44struct PostRAHazardRecognizer {45 bool run(MachineFunction &MF);46};47 48class PostRAHazardRecognizerLegacy : public MachineFunctionPass {49 50public:51 static char ID;52 PostRAHazardRecognizerLegacy() : MachineFunctionPass(ID) {}53 54 void getAnalysisUsage(AnalysisUsage &AU) const override {55 AU.setPreservesCFG();56 MachineFunctionPass::getAnalysisUsage(AU);57 }58 59 bool runOnMachineFunction(MachineFunction &Fn) override {60 return PostRAHazardRecognizer().run(Fn);61 }62};63char PostRAHazardRecognizerLegacy::ID = 0;64 65} // namespace66 67char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizerLegacy::ID;68 69INITIALIZE_PASS(PostRAHazardRecognizerLegacy, DEBUG_TYPE,70 "Post RA hazard recognizer", false, false)71 72PreservedAnalyses73llvm::PostRAHazardRecognizerPass::run(MachineFunction &MF,74 MachineFunctionAnalysisManager &MFAM) {75 if (!PostRAHazardRecognizer().run(MF))76 return PreservedAnalyses::all();77 78 auto PA = getMachineFunctionPassPreservedAnalyses();79 PA.preserveSet<CFGAnalyses>();80 return PA;81}82 83bool PostRAHazardRecognizer::run(MachineFunction &Fn) {84 const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();85 std::unique_ptr<ScheduleHazardRecognizer> HazardRec(86 TII->CreateTargetPostRAHazardRecognizer(Fn));87 88 // Return if the target has not implemented a hazard recognizer.89 if (!HazardRec)90 return false;91 92 // Loop over all of the basic blocks93 bool Changed = false;94 for (auto &MBB : Fn) {95 // We do not call HazardRec->reset() here to make sure we are handling noop96 // hazards at the start of basic blocks.97 for (MachineInstr &MI : MBB) {98 // If we need to emit noops prior to this instruction, then do so.99 unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);100 HazardRec->EmitNoops(NumPreNoops);101 TII->insertNoops(MBB, MachineBasicBlock::iterator(MI), NumPreNoops);102 NumNoops += NumPreNoops;103 if (NumPreNoops)104 Changed = true;105 106 HazardRec->EmitInstruction(&MI);107 if (HazardRec->atIssueLimit()) {108 HazardRec->AdvanceCycle();109 }110 }111 }112 return Changed;113}114