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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/IR/Instructions.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/CommandLine.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;
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;
}
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;
}
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