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-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 /// \file 10 /// This runs the hazard recognizer and emits noops when necessary. This 11 /// gives targets a way to run the hazard recognizer without running one of 12 /// 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 of 16 /// scheduling regions are handled correctly. The post-RA scheduler is 17 /// a top-down scheduler, but when there are multiple scheduling regions 18 /// in a basic block, it visits the regions in bottom-up order. This 19 /// makes it impossible for the scheduler to gauranttee it can correctly 20 /// 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 resets 24 /// the hazard recognizer to ensure it can correctly handles noop hazards at 25 /// 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" 37 using namespace llvm; 38 39 #define DEBUG_TYPE "post-RA-hazard-rec" 40 41 STATISTIC(NumNoops, "Number of noops inserted"); 42 43 namespace { 44 struct PostRAHazardRecognizer { 45 bool run(MachineFunction &MF); 46 }; 47 48 class PostRAHazardRecognizerLegacy : public MachineFunctionPass { 49 50 public: 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 }; 63 char PostRAHazardRecognizerLegacy::ID = 0; 64 65 } // namespace 66 67 char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizerLegacy::ID; 68 69 INITIALIZE_PASS(PostRAHazardRecognizerLegacy, DEBUG_TYPE, 70 "Post RA hazard recognizer", false, false) 71 72 PreservedAnalyses 73 llvm::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 83 bool 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 blocks 93 bool Changed = false; 94 for (auto &MBB : Fn) { 95 // We do not call HazardRec->reset() here to make sure we are handling noop 96 // 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