LLVM  9.0.0svn
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/Support/Debug.h"
38 using namespace llvm;
39 
40 #define DEBUG_TYPE "post-RA-hazard-rec"
41 
42 STATISTIC(NumNoops, "Number of noops inserted");
43 
44 namespace {
45  class PostRAHazardRecognizer : public MachineFunctionPass {
46 
47  public:
48  static char ID;
49  PostRAHazardRecognizer() : MachineFunctionPass(ID) {}
50 
51  void getAnalysisUsage(AnalysisUsage &AU) const override {
52  AU.setPreservesCFG();
54  }
55 
56  bool runOnMachineFunction(MachineFunction &Fn) override;
57 
58  };
60 
61 }
62 
64 
65 INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE,
66  "Post RA hazard recognizer", false, false)
67 
68 bool PostRAHazardRecognizer::runOnMachineFunction(MachineFunction &Fn) {
69  const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
70  std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
72 
73  // Return if the target has not implemented a hazard recognizer.
74  if (!HazardRec.get())
75  return false;
76 
77  // Loop over all of the basic blocks
78  for (auto &MBB : Fn) {
79  // We do not call HazardRec->reset() here to make sure we are handling noop
80  // hazards at the start of basic blocks.
81  for (MachineInstr &MI : MBB) {
82  // If we need to emit noops prior to this instruction, then do so.
83  unsigned NumPreNoops = HazardRec->PreEmitNoops(&MI);
84  for (unsigned i = 0; i != NumPreNoops; ++i) {
85  HazardRec->EmitNoop();
87  ++NumNoops;
88  }
89 
90  HazardRec->EmitInstruction(&MI);
91  if (HazardRec->atIssueLimit()) {
92  HazardRec->AdvanceCycle();
93  }
94  }
95  }
96  return true;
97 }
This class represents lattice values for constants.
Definition: AllocatorList.h:23
INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE, "Post RA hazard recognizer", false, false) bool PostRAHazardRecognizer
STATISTIC(NumFunctions, "Total number of functions")
MachineFunctionPass - This class adapts the FunctionPass interface to allow convenient creation of pa...
const HexagonInstrInfo * TII
TargetInstrInfo - Interface to description of machine instruction set.
void getAnalysisUsage(AnalysisUsage &AU) const override
getAnalysisUsage - Subclasses that override getAnalysisUsage must call this.
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:301
virtual void insertNoop(MachineBasicBlock &MBB, MachineBasicBlock::iterator MI) const
Insert a noop into the instruction stream at the specified point.
Representation of each machine instruction.
Definition: MachineInstr.h:63
#define DEBUG_TYPE
char & PostRAHazardRecognizerID
createPostRAHazardRecognizer - This pass runs the post-ra hazard recognizer.
IRTranslator LLVM IR MI
virtual ScheduleHazardRecognizer * CreateTargetPostRAHazardRecognizer(const InstrItineraryData *, const ScheduleDAG *DAG) const
Allocate and return a hazard recognizer to use for this target when scheduling the machine instructio...