1 //===----- PostRAHazardRecognizer.cpp - hazard recognizer -----------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 /// \file
11 /// This runs the hazard recognizer and emits noops when necessary. This
12 /// gives targets a way to run the hazard recognizer without running one of
13 /// the schedulers. Example use cases for this pass would be:
14 ///
15 /// - Targets that need the hazard recognizer to be run at -O0.
16 /// - Targets that want to guarantee that hazards at the beginning of
17 /// scheduling regions are handled correctly. The post-RA scheduler is
18 /// a top-down scheduler, but when there are multiple scheduling regions
19 /// in a basic block, it visits the regions in bottom-up order. This
20 /// makes it impossible for the scheduler to gauranttee it can correctly
21 /// handle hazards at the beginning of scheduling regions.
22 ///
23 /// This pass traverses all the instructions in a program in top-down order.
24 /// In contrast to the instruction scheduling passes, this pass never resets
25 /// the hazard recognizer to ensure it can correctly handles noop hazards at
26 /// the begining of blocks.
27 //
28 //===----------------------------------------------------------------------===//
29
30 #include "llvm/CodeGen/Passes.h"
31 #include "llvm/ADT/Statistic.h"
32 #include "llvm/CodeGen/MachineFunctionPass.h"
33 #include "llvm/CodeGen/ScheduleHazardRecognizer.h"
34 #include "llvm/Support/Debug.h"
35 #include "llvm/Support/ErrorHandling.h"
36 #include "llvm/Support/raw_ostream.h"
37 #include "llvm/Target/TargetInstrInfo.h"
38 #include "llvm/Target/TargetSubtargetInfo.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;
PostRAHazardRecognizer()50 PostRAHazardRecognizer() : MachineFunctionPass(ID) {}
51
getAnalysisUsage(AnalysisUsage & AU) const52 void getAnalysisUsage(AnalysisUsage &AU) const override {
53 AU.setPreservesCFG();
54 MachineFunctionPass::getAnalysisUsage(AU);
55 }
56
57 bool runOnMachineFunction(MachineFunction &Fn) override;
58
59 };
60 char PostRAHazardRecognizer::ID = 0;
61
62 }
63
64 char &llvm::PostRAHazardRecognizerID = PostRAHazardRecognizer::ID;
65
66 INITIALIZE_PASS(PostRAHazardRecognizer, DEBUG_TYPE,
67 "Post RA hazard recognizer", false, false)
68
runOnMachineFunction(MachineFunction & Fn)69 bool PostRAHazardRecognizer::runOnMachineFunction(MachineFunction &Fn) {
70 const TargetInstrInfo *TII = Fn.getSubtarget().getInstrInfo();
71 std::unique_ptr<ScheduleHazardRecognizer> HazardRec(
72 TII->CreateTargetPostRAHazardRecognizer(Fn));
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 for (unsigned i = 0; i != NumPreNoops; ++i) {
86 HazardRec->EmitNoop();
87 TII->insertNoop(MBB, MachineBasicBlock::iterator(MI));
88 ++NumNoops;
89 }
90
91 HazardRec->EmitInstruction(&MI);
92 if (HazardRec->atIssueLimit()) {
93 HazardRec->AdvanceCycle();
94 }
95 }
96 }
97 return true;
98 }
99