text: //===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // This analysis uses probability info stored in Machine Basic Blocks.
  //
  //===----------------------------------------------------------------------===//
  
  #include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
  #include "llvm/CodeGen/MachineBasicBlock.h"
  #include "llvm/IR/Instructions.h"
  #include "llvm/Support/Debug.h"
  #include "llvm/Support/raw_ostream.h"
  
  using namespace llvm;
  
  INITIALIZE_PASS_BEGIN(MachineBranchProbabilityInfo, "machine-branch-prob",
                        "Machine Branch Probability Analysis", false, true)
  INITIALIZE_PASS_END(MachineBranchProbabilityInfo, "machine-branch-prob",
                      "Machine Branch Probability Analysis", false, true)
  
  cl::opt<unsigned>
      StaticLikelyProb("static-likely-prob",
                       cl::desc("branch probability threshold in percentage"
                                "to be considered very likely"),
                       cl::init(80), cl::Hidden);
  
  cl::opt<unsigned> ProfileLikelyProb(
      "profile-likely-prob",
      cl::desc("branch probability threshold in percentage to be considered"
               " very likely when profile is available"),
      cl::init(51), cl::Hidden);
  
  char MachineBranchProbabilityInfo::ID = 0;
  
  void MachineBranchProbabilityInfo::anchor() {}
  
  BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
      const MachineBasicBlock *Src,
      MachineBasicBlock::const_succ_iterator Dst) const {
    return Src->getSuccProbability(Dst);
  }
  
  BranchProbability MachineBranchProbabilityInfo::getEdgeProbability(
      const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
    // This is a linear search. Try to use the const_succ_iterator version when
    // possible.
    return getEdgeProbability(Src, find(Src->successors(), Dst));
  }
  
  bool MachineBranchProbabilityInfo::isEdgeHot(
      const MachineBasicBlock *Src, const MachineBasicBlock *Dst) const {
    BranchProbability HotProb(StaticLikelyProb, 100);
    return getEdgeProbability(Src, Dst) > HotProb;
  }
  
  MachineBasicBlock *
  MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
    auto MaxProb = BranchProbability::getZero();
    MachineBasicBlock *MaxSucc = nullptr;
    for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
         E = MBB->succ_end(); I != E; ++I) {
      auto Prob = getEdgeProbability(MBB, I);
      if (Prob > MaxProb) {
        MaxProb = Prob;
        MaxSucc = *I;
      }
    }
  
    BranchProbability HotProb(StaticLikelyProb, 100);
    if (getEdgeProbability(MBB, MaxSucc) >= HotProb)
      return MaxSucc;
  
    return nullptr;
  }
  
  raw_ostream &MachineBranchProbabilityInfo::printEdgeProbability(
      raw_ostream &OS, const MachineBasicBlock *Src,
      const MachineBasicBlock *Dst) const {
  
    const BranchProbability Prob = getEdgeProbability(Src, Dst);
    OS << "edge " << printMBBReference(*Src) << " -> " << printMBBReference(*Dst)
       << " probability is " << Prob
       << (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
  
    return OS;
  }
  