LLVM  14.0.0git
PostRAHazardRecognizer.cpp
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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"
31 #include "llvm/CodeGen/Passes.h"
35 #include "llvm/InitializePasses.h"
36 #include "llvm/Support/Debug.h"
39 using namespace llvm;
40 
41 #define DEBUG_TYPE "post-RA-hazard-rec"
42 
43 STATISTIC(NumNoops, "Number of noops inserted");
44 
45 namespace {
46  class PostRAHazardRecognizer : public MachineFunctionPass {
47 
48  public:
49  static char ID;
50  PostRAHazardRecognizer() : MachineFunctionPass(ID) {}
51 
52  void getAnalysisUsage(AnalysisUsage &AU) const override {
53  AU.setPreservesCFG();
55  }
56 
57  bool runOnMachineFunction(MachineFunction &Fn) override;
58 
59  };
61 
62 }
63 
65 
66 INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE,
67  "Post RA hazard recognizer", false, false)
68 
69 bool PostRAHazardRecognizer::runOnMachineFunction(MachineFunction &Fn) {
70  const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
71  std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
73 
74  // Return if the target has not implemented a hazard recognizer.
75  if (!HazardRec.get())
76  return false;
77 
78  // Loop over all of the basic blocks
79  for (auto &MBB : Fn) {
80  // We do not call HazardRec->reset() here to make sure we are handling noop
81  // hazards at the start of basic blocks.
82  for (MachineInstr &MI : MBB) {
83  // If we need to emit noops prior to this instruction, then do so.
84  unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);
85  HazardRec->EmitNoops(NumPreNoops);
86  TII->insertNoops(MBB, MachineBasicBlock::iterator(MI), NumPreNoops);
87  NumNoops += NumPreNoops;
88 
89  HazardRec->EmitInstruction(&MI);
90  if (HazardRec->atIssueLimit()) {
91  HazardRec->AdvanceCycle();
92  }
93  }
94  }
95  return true;
96 }
MI
IRTranslator LLVM IR MI
Definition: IRTranslator.cpp:105
llvm
This file implements support for optimizing divisions by a constant.
Definition: AllocatorList.h:23
Statistic.h
ErrorHandling.h
llvm::MachineFunctionPass
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
Definition: MachineFunctionPass.h:30
TargetInstrInfo.h
llvm::MachineFunctionPass::getAnalysisUsage
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
Definition: MachineFunctionPass.cpp:102
ScheduleHazardRecognizer.h
llvm::TargetInstrInfo
TargetInstrInfo - Interface to description of machine instruction set.
Definition: TargetInstrInfo.h:97
llvm::PostRAHazardRecognizerID
char & PostRAHazardRecognizerID
PostRAHazardRecognizer - This pass runs the post-ra hazard recognizer.
Definition: PostRAHazardRecognizer.cpp:64
llvm::AnalysisUsage
Represent the analysis usage information of a pass.
Definition: PassAnalysisSupport.h:47
TII
const HexagonInstrInfo * TII
Definition: HexagonCopyToCombine.cpp:129
llvm::STATISTIC
STATISTIC(NumFunctions, "Total number of functions")
Passes.h
llvm::MachineInstr
Representation of each machine instruction.
Definition: MachineInstr.h:64
MachineFunctionPass.h
llvm::HexagonInstrInfo::CreateTargetPostRAHazardRecognizer
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...
Definition: HexagonInstrInfo.cpp:1782
llvm::MachineFunction
Definition: MachineFunction.h:234
llvm::AnalysisUsage::setPreservesCFG
void setPreservesCFG()
This function should be called by the pass, iff they do not:
Definition: Pass.cpp:253
TargetSubtargetInfo.h
MBB
MachineBasicBlock & MBB
Definition: AArch64SLSHardening.cpp:74
INITIALIZE_PASS
INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE, "Post RA hazard recognizer", false, false) bool PostRAHazardRecognizer
Definition: PostRAHazardRecognizer.cpp:66
raw_ostream.h
llvm::MachineInstrBundleIterator< MachineInstr >
InitializePasses.h
Debug.h
DEBUG_TYPE
#define DEBUG_TYPE
Definition: PostRAHazardRecognizer.cpp:41
llvm::Intrinsic::ID
unsigned ID
Definition: TargetTransformInfo.h:37