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//===- MachineBranchProbabilityInfo.cpp - Machine Branch Probability Info -===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This analysis uses probability info stored in Machine Basic Blocks.
//
//===----------------------------------------------------------------------===//
#include "llvm/Instructions.h"
#include "llvm/CodeGen/MachineBranchProbabilityInfo.h"
#include "llvm/CodeGen/MachineBasicBlock.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)
char MachineBranchProbabilityInfo::ID = 0;
uint32_t MachineBranchProbabilityInfo::
getSumForBlock(MachineBasicBlock *MBB) const {
uint32_t Sum = 0;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
MachineBasicBlock *Succ = *I;
uint32_t Weight = getEdgeWeight(MBB, Succ);
uint32_t PrevSum = Sum;
Sum += Weight;
assert(Sum > PrevSum); (void) PrevSum;
}
return Sum;
}
uint32_t
MachineBranchProbabilityInfo::getEdgeWeight(MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
uint32_t Weight = Src->getSuccWeight(Dst);
if (!Weight)
return DEFAULT_WEIGHT;
return Weight;
}
bool MachineBranchProbabilityInfo::isEdgeHot(MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
// Hot probability is at least 4/5 = 80%
uint32_t Weight = getEdgeWeight(Src, Dst);
uint32_t Sum = getSumForBlock(Src);
// FIXME: Implement BranchProbability::compare then change this code to
// compare this BranchProbability against a static "hot" BranchProbability.
return (uint64_t)Weight * 5 > (uint64_t)Sum * 4;
}
MachineBasicBlock *
MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
uint32_t Sum = 0;
uint32_t MaxWeight = 0;
MachineBasicBlock *MaxSucc = 0;
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
E = MBB->succ_end(); I != E; ++I) {
MachineBasicBlock *Succ = *I;
uint32_t Weight = getEdgeWeight(MBB, Succ);
uint32_t PrevSum = Sum;
Sum += Weight;
assert(Sum > PrevSum); (void) PrevSum;
if (Weight > MaxWeight) {
MaxWeight = Weight;
MaxSucc = Succ;
}
}
// FIXME: Use BranchProbability::compare.
if ((uint64_t)MaxWeight * 5 >= (uint64_t)Sum * 4)
return MaxSucc;
return 0;
}
BranchProbability
MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
uint32_t N = getEdgeWeight(Src, Dst);
uint32_t D = getSumForBlock(Src);
return BranchProbability(N, D);
}
raw_ostream &MachineBranchProbabilityInfo::
printEdgeProbability(raw_ostream &OS, MachineBasicBlock *Src,
MachineBasicBlock *Dst) const {
const BranchProbability Prob = getEdgeProbability(Src, Dst);
OS << "edge MBB#" << Src->getNumber() << " -> MBB#" << Dst->getNumber()
<< " probability is " << Prob
<< (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
return OS;
}
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