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"
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(MF&: Fn);
61 }
62};
63char PostRAHazardRecognizerLegacy::ID = 0;
64
65} // namespace
66
67char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizerLegacy::ID;
68
69INITIALIZE_PASS(PostRAHazardRecognizerLegacy, DEBUG_TYPE,
70 "Post RA hazard recognizer", false, false)
71
72PreservedAnalyses
73llvm::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(MF: 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(Quantity: NumPreNoops);
101 TII->insertNoops(MBB, MI: MachineBasicBlock::iterator(MI), Quantity: 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