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/IR/Instructions.h"
  16 #include "llvm/InitializePasses.h"
  17 #include "llvm/Support/CommandLine.h"
  18 #include "llvm/Support/Debug.h"
  19 #include "llvm/Support/raw_ostream.h"
  20
  21 using namespace llvm;
  22
  23 INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
  24                       "Machine Branch Probability Analysis", false, true)
  25 INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "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 char MachineBranchProbabilityInfo::ID = 0;
  43
  44 MachineBranchProbabilityInfo::MachineBranchProbabilityInfo()
  45     : ImmutablePass(ID) {
  46   PassRegistry &Registry = *PassRegistry::getPassRegistry();
  47   initializeMachineBranchProbabilityInfoPass(Registry);
  48 }
  49
  50 void MachineBranchProbabilityInfo::anchor() {}
  51
  52 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
  53     const MachineBasicBlock *Src,
  54     MachineBasicBlock::const_succ_iterator Dst) const {
  55   return Src->getSuccProbability(Dst);
  56 }
  57
  58 BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
  59     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
  60   // This is a linear search. Try to use the const_succ_iterator version when
  61   // possible.
  62   return getEdgeProbability(Src, find(Src->successors(), Dst));
  63 }
  64
  65 bool MachineBranchProbabilityInfo::isEdgeHot(
  66     const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
  67   BranchProbability HotProb(StaticLikelyProb, 100);
  68   return getEdgeProbability(Src, Dst) > HotProb;
  69 }
  70
  71 raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
  72     raw_ostream &OS, const MachineBasicBlock *Src,
  73     const MachineBasicBlock *Dst) const {
  74
  75   const BranchProbability Prob = getEdgeProbability(Src, Dst);
  76   OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
  77      << " probability is " << Prob
  78      << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
  79
  80   return OS;
  81 }