MachineBranchProbabilityInfo.cpp

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//===- 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/InitializePasses.h"
#include "llvm/Support/CommandLine.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)
 
namespace llvm {
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);
} // namespace llvm
 
char MachineBranchProbabilityInfo::ID = 0;
 
MachineBranchProbabilityInfo::MachineBranchProbabilityInfo()
    : ImmutablePass(ID) {
  PassRegistry &Registry = *PassRegistry::getPassRegistry();
  initializeMachineBranchProbabilityInfoPass(Registry);
}
 
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;
}
 
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;
}