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/MachineLoopInfo.h"
33#include "llvm/CodeGen/ScheduleHazardRecognizer.h"
34#include "llvm/CodeGen/TargetInstrInfo.h"
35#include "llvm/CodeGen/TargetSubtargetInfo.h"
36#include "llvm/InitializePasses.h"
37#include "llvm/Pass.h"
38using namespace llvm;
39
40#define DEBUG_TYPE "post-RA-hazard-rec"
41
42STATISTIC(NumNoops, "Number of noops inserted");
43
44namespace {
45struct PostRAHazardRecognizer {
46 bool run(MachineFunction &MF, MachineLoopInfo *MLI);
47};
48
49class PostRAHazardRecognizerLegacy : public MachineFunctionPass {
50
51public:
52 static char ID;
53 PostRAHazardRecognizerLegacy() : MachineFunctionPass(ID) {}
54
55 void getAnalysisUsage(AnalysisUsage &AU) const override {
56 AU.setPreservesCFG();
57 AU.addRequired<MachineLoopInfoWrapperPass>();
58 MachineFunctionPass::getAnalysisUsage(AU);
59 }
60
61 bool runOnMachineFunction(MachineFunction &Fn) override {
62 MachineLoopInfo &MLI = getAnalysis<MachineLoopInfoWrapperPass>().getLI();
63 return PostRAHazardRecognizer().run(MF&: Fn, MLI: &MLI);
64 }
65};
66char PostRAHazardRecognizerLegacy::ID = 0;
67
68} // namespace
69
70char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizerLegacy::ID;
71
72INITIALIZE_PASS_BEGIN(PostRAHazardRecognizerLegacy, DEBUG_TYPE,
73 "Post RA hazard recognizer", false, false)
74INITIALIZE_PASS_DEPENDENCY(MachineLoopInfoWrapperPass)
75INITIALIZE_PASS_END(PostRAHazardRecognizerLegacy, DEBUG_TYPE,
76 "Post RA hazard recognizer", false, false)
77
78PreservedAnalyses
79llvm::PostRAHazardRecognizerPass::run(MachineFunction &MF,
80 MachineFunctionAnalysisManager &MFAM) {
81 MachineLoopInfo *MLI = &MFAM.getResult<MachineLoopAnalysis>(IR&: MF);
82 if (!PostRAHazardRecognizer().run(MF, MLI))
83 return PreservedAnalyses::all();
84
85 auto PA = getMachineFunctionPassPreservedAnalyses();
86 PA.preserveSet<CFGAnalyses>();
87 return PA;
88}
89
90bool PostRAHazardRecognizer::run(MachineFunction &Fn, MachineLoopInfo *MLI) {
91 const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
92 std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
93 TII->CreateTargetPostRAHazardRecognizer(MF: Fn, MLI));
94
95 // Return if the target has not implemented a hazard recognizer.
96 if (!HazardRec)
97 return false;
98
99 // Loop over all of the basic blocks
100 bool Changed = false;
101 for (auto &MBB : Fn) {
102 // We do not call HazardRec->reset() here to make sure we are handling noop
103 // hazards at the start of basic blocks.
104 for (MachineInstr &MI : MBB) {
105 // If we need to emit noops prior to this instruction, then do so.
106 unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);
107 HazardRec->EmitNoops(Quantity: NumPreNoops);
108 TII->insertNoops(MBB, MI: MachineBasicBlock::iterator(MI), Quantity: NumPreNoops);
109 NumNoops += NumPreNoops;
110 if (NumPreNoops)
111 Changed = true;
112
113 HazardRec->EmitInstruction(&MI);
114 if (HazardRec->atIssueLimit()) {
115 HazardRec->AdvanceCycle();
116 }
117 }
118 }
119 return Changed;
120}
121