llvm/lib/CodeGen/MachineBranchProbabilityInfo.cpp

   1 //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
   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 // This analysis uses probability info stored in Machine Basic Blocks.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
  14 #include "llvm/CodeGen/MachineBasicBlock.h"
  15 #include "llvm/InitializePasses.h"
  16 #include "llvm/Support/CommandLine.h"
  17 #include "llvm/Support/raw_ostream.h"
  18
  19 using namespace llvm;
  20
  21 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfoWrapperPass,
  22                       "machine-branch-prob",
  23                       "Machine Branch Probability Analysis", false, true)
  24 INITIALIZE_PASS_END(MachineBranchProbabilityInfoWrapperPass,
  25                     "machine-branch-prob",
  26                     "Machine Branch Probability Analysis", false, true)
  27
  28 namespace llvm {
  29 cl::opt<unsigned>
  30     StaticLikelyProb("static-likely-prob",
  31                      cl::desc("branch probability threshold in percentage"
  32                               "to be considered very likely"),
  33                      cl::init(80), cl::Hidden);
  34
  35 cl::opt<unsigned> ProfileLikelyProb(
  36     "profile-likely-prob",
  37     cl::desc("branch probability threshold in percentage to be considered"
  38              " very likely when profile is available"),
  39     cl::init(51), cl::Hidden);
  40 } // namespace llvm
  41
  42 MachineBranchProbabilityAnalysis::Result
  43 MachineBranchProbabilityAnalysis::run(MachineFunction &,
  44                                       MachineFunctionAnalysisManager &) {
  45   return MachineBranchProbabilityInfo();
  46 }
  47
  48 PreservedAnalyses
  49 MachineBranchProbabilityPrinterPass::run(MachineFunction &MF,
  50                                          MachineFunctionAnalysisManager &MFAM) {
  51   OS << "Printing analysis 'Machine Branch Probability Analysis' for machine "
  52         "function '"
  53      << MF.getName() << "':\n";
  54   auto &MBPI = MFAM.getResult<MachineBranchProbabilityAnalysis>(MF);
  55   for (const MachineBasicBlock &MBB : MF) {
  56     for (const MachineBasicBlock *Succ : MBB.successors())
  57       MBPI.printEdgeProbability(OS << "  ", &MBB, Succ);
  58   }
  59   return PreservedAnalyses::all();
  60 }
  61
  62 char MachineBranchProbabilityInfoWrapperPass::ID = 0;
  63
  64 MachineBranchProbabilityInfoWrapperPass::
  65     MachineBranchProbabilityInfoWrapperPass()
  66     : ImmutablePass(ID) {
  67   PassRegistry &Registry = *PassRegistry::getPassRegistry();
  68   initializeMachineBranchProbabilityInfoWrapperPassPass(Registry);
  69 }
  70
  71 void MachineBranchProbabilityInfoWrapperPass::anchor() {}
  72
  73 AnalysisKey MachineBranchProbabilityAnalysis::Key;
  74
  75 bool MachineBranchProbabilityInfo::invalidate(
  76     MachineFunction &, const PreservedAnalyses &PA,
  77     MachineFunctionAnalysisManager::Invalidator &) {
  78   auto PAC = PA.getChecker<MachineBranchProbabilityAnalysis>();
  79   return !PAC.preservedWhenStateless();
  80 }
  81
  82 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
  83     const MachineBasicBlock *Src,
  84     MachineBasicBlock::const_succ_iterator Dst) const {
  85   return Src->getSuccProbability(Dst);
  86 }
  87
  88 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
  89     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
  90   // This is a linear search. Try to use the const_succ_iterator version when
  91   // possible.
  92   return getEdgeProbability(Src, find(Src->successors(), Dst));
  93 }
  94
  95 bool MachineBranchProbabilityInfo::isEdgeHot(
  96     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
  97   BranchProbability HotProb(StaticLikelyProb, 100);
  98   return getEdgeProbability(Src, Dst) > HotProb;
  99 }
 100
 101 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
 102     raw_ostream &OS, const MachineBasicBlock *Src,
 103     const MachineBasicBlock *Dst) const {
 104
 105   const BranchProbability Prob = getEdgeProbability(Src, Dst);
 106   OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
 107      << " probability is " << Prob
 108      << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
 109
 110   return OS;
 111 }