LLVM 20.0.0git
PostRAHazardRecognizer.cpp
Go to the documentation of this file.
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/ADT/Statistic.h"
35#include "llvm/Pass.h"
36using namespace llvm;
37
38#define DEBUG_TYPE "post-RA-hazard-rec"
39
40STATISTIC(NumNoops, "Number of noops inserted");
41
42namespace {
43 class PostRAHazardRecognizer : public MachineFunctionPass {
44
45 public:
46 static char ID;
47 PostRAHazardRecognizer() : MachineFunctionPass(ID) {}
48
49 void getAnalysisUsage(AnalysisUsage &AU) const override {
50 AU.setPreservesCFG();
52 }
53
54 bool runOnMachineFunction(MachineFunction &Fn) override;
55
56 };
57 char PostRAHazardRecognizer::ID = 0;
58
59}
60
61char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizer::ID;
62
63INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE,
64 "Post RA hazard recognizer", false, false)
65
66bool PostRAHazardRecognizer::runOnMachineFunction(MachineFunction &Fn) {
67 const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
68 std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
70
71 // Return if the target has not implemented a hazard recognizer.
72 if (!HazardRec)
73 return false;
74
75 // Loop over all of the basic blocks
76 bool Changed = false;
77 for (auto &MBB : Fn) {
78 // We do not call HazardRec->reset() here to make sure we are handling noop
79 // hazards at the start of basic blocks.
80 for (MachineInstr &MI : MBB) {
81 // If we need to emit noops prior to this instruction, then do so.
82 unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);
83 HazardRec->EmitNoops(NumPreNoops);
84 TII->insertNoops(MBB, MachineBasicBlock::iterator(MI), NumPreNoops);
85 NumNoops += NumPreNoops;
86 if (NumPreNoops)
87 Changed = true;
88
89 HazardRec->EmitInstruction(&MI);
90 if (HazardRec->atIssueLimit()) {
91 HazardRec->AdvanceCycle();
92 }
93 }
94 }
95 return Changed;
96}
MachineBasicBlock & MBB
const HexagonInstrInfo * TII
IRTranslator LLVM IR MI
#define INITIALIZE_PASS(passName, arg, name, cfg, analysis)
Definition: PassSupport.h:38
#define DEBUG_TYPE
This file defines the 'Statistic' class, which is designed to be an easy way to expose various metric...
#define STATISTIC(VARNAME, DESC)
Definition: Statistic.h:167
Represent the analysis usage information of a pass.
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:256
ScheduleHazardRecognizer * CreateTargetPostRAHazardRecognizer(const InstrItineraryData *II, const ScheduleDAG *DAG) const override
Allocate and return a hazard recognizer to use for this target when scheduling the machine instructio...
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
virtual bool runOnMachineFunction(MachineFunction &MF)=0
runOnMachineFunction - This method must be overloaded to perform the desired machine code transformat...
Representation of each machine instruction.
Definition: MachineInstr.h:69
TargetInstrInfo - Interface to description of machine instruction set.
unsigned ID
LLVM IR allows to use arbitrary numbers as calling convention identifiers.
Definition: CallingConv.h:24
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
char & PostRAHazardRecognizerID
PostRAHazardRecognizer - This pass runs the post-ra hazard recognizer.