mirror of
https://github.com/RPCSX/llvm.git
synced 2024-11-28 22:20:37 +00:00
25101bb2a7
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146986 91177308-0d34-0410-b5e6-96231b3b80d8
119 lines
3.9 KiB
C++
119 lines
3.9 KiB
C++
//===- 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;
|
|
|
|
void MachineBranchProbabilityInfo::anchor() { }
|
|
|
|
uint32_t MachineBranchProbabilityInfo::
|
|
getSumForBlock(const MachineBasicBlock *MBB, uint32_t &Scale) const {
|
|
// First we compute the sum with 64-bits of precision, ensuring that cannot
|
|
// overflow by bounding the number of weights considered. Hopefully no one
|
|
// actually needs 2^32 successors.
|
|
assert(MBB->succ_size() < UINT32_MAX);
|
|
uint64_t Sum = 0;
|
|
Scale = 1;
|
|
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
|
|
E = MBB->succ_end(); I != E; ++I) {
|
|
uint32_t Weight = getEdgeWeight(MBB, *I);
|
|
Sum += Weight;
|
|
}
|
|
|
|
// If the computed sum fits in 32-bits, we're done.
|
|
if (Sum <= UINT32_MAX)
|
|
return Sum;
|
|
|
|
// Otherwise, compute the scale necessary to cause the weights to fit, and
|
|
// re-sum with that scale applied.
|
|
assert((Sum / UINT32_MAX) < UINT32_MAX);
|
|
Scale = (Sum / UINT32_MAX) + 1;
|
|
Sum = 0;
|
|
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
|
|
E = MBB->succ_end(); I != E; ++I) {
|
|
uint32_t Weight = getEdgeWeight(MBB, *I);
|
|
Sum += Weight / Scale;
|
|
}
|
|
assert(Sum <= UINT32_MAX);
|
|
return Sum;
|
|
}
|
|
|
|
uint32_t
|
|
MachineBranchProbabilityInfo::getEdgeWeight(const MachineBasicBlock *Src,
|
|
const 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%
|
|
// FIXME: Compare against a static "hot" BranchProbability.
|
|
return getEdgeProbability(Src, Dst) > BranchProbability(4, 5);
|
|
}
|
|
|
|
MachineBasicBlock *
|
|
MachineBranchProbabilityInfo::getHotSucc(MachineBasicBlock *MBB) const {
|
|
uint32_t MaxWeight = 0;
|
|
MachineBasicBlock *MaxSucc = 0;
|
|
for (MachineBasicBlock::const_succ_iterator I = MBB->succ_begin(),
|
|
E = MBB->succ_end(); I != E; ++I) {
|
|
uint32_t Weight = getEdgeWeight(MBB, *I);
|
|
if (Weight > MaxWeight) {
|
|
MaxWeight = Weight;
|
|
MaxSucc = *I;
|
|
}
|
|
}
|
|
|
|
if (getEdgeProbability(MBB, MaxSucc) >= BranchProbability(4, 5))
|
|
return MaxSucc;
|
|
|
|
return 0;
|
|
}
|
|
|
|
BranchProbability
|
|
MachineBranchProbabilityInfo::getEdgeProbability(MachineBasicBlock *Src,
|
|
MachineBasicBlock *Dst) const {
|
|
uint32_t Scale = 1;
|
|
uint32_t D = getSumForBlock(Src, Scale);
|
|
uint32_t N = getEdgeWeight(Src, Dst) / Scale;
|
|
|
|
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;
|
|
}
|