mirror of
https://github.com/c64scene-ar/llvm-6502.git
synced 2024-08-28 06:29:45 +00:00
Patch by: Jakub Staszak! Introduces BranchProbability. Changes unsigned to uint32_t all over and uint64_t only when overflow is expected. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132867 91177308-0d34-0410-b5e6-96231b3b80d8
358 lines
10 KiB
C++
358 lines
10 KiB
C++
//===-- BranchProbabilityInfo.cpp - Branch Probability Analysis -*- C++ -*-===//
|
|
//
|
|
// The LLVM Compiler Infrastructure
|
|
//
|
|
// This file is distributed under the University of Illinois Open Source
|
|
// License. See LICENSE.TXT for details.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// Loops should be simplified before this analysis.
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#include "llvm/Instructions.h"
|
|
#include "llvm/Analysis/BranchProbabilityInfo.h"
|
|
#include "llvm/Support/Debug.h"
|
|
|
|
using namespace llvm;
|
|
|
|
INITIALIZE_PASS_BEGIN(BranchProbabilityInfo, "branch-prob",
|
|
"Branch Probability Analysis", false, true)
|
|
INITIALIZE_PASS_DEPENDENCY(LoopInfo)
|
|
INITIALIZE_PASS_END(BranchProbabilityInfo, "branch-prob",
|
|
"Branch Probability Analysis", false, true)
|
|
|
|
char BranchProbabilityInfo::ID = 0;
|
|
|
|
|
|
// Please note that BranchProbabilityAnalysis is not a FunctionPass.
|
|
// It is created by BranchProbabilityInfo (which is a FunctionPass), which
|
|
// provides a clear interface. Thanks to that, all heuristics and other
|
|
// private methods are hidden in the .cpp file.
|
|
class BranchProbabilityAnalysis {
|
|
|
|
typedef std::pair<BasicBlock *, BasicBlock *> Edge;
|
|
|
|
DenseMap<Edge, uint32_t> *Weights;
|
|
|
|
BranchProbabilityInfo *BP;
|
|
|
|
LoopInfo *LI;
|
|
|
|
|
|
// Weights are for internal use only. They are used by heuristics to help to
|
|
// estimate edges' probability. Example:
|
|
//
|
|
// Using "Loop Branch Heuristics" we predict weights of edges for the
|
|
// block BB2.
|
|
// ...
|
|
// |
|
|
// V
|
|
// BB1<-+
|
|
// | |
|
|
// | | (Weight = 128)
|
|
// V |
|
|
// BB2--+
|
|
// |
|
|
// | (Weight = 4)
|
|
// V
|
|
// BB3
|
|
//
|
|
// Probability of the edge BB2->BB1 = 128 / (128 + 4) = 0.9696..
|
|
// Probability of the edge BB2->BB3 = 4 / (128 + 4) = 0.0303..
|
|
|
|
static const uint32_t LBH_TAKEN_WEIGHT = 128;
|
|
static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
|
|
|
|
// Standard weight value. Used when none of the heuristics set weight for
|
|
// the edge.
|
|
static const uint32_t NORMAL_WEIGHT = 16;
|
|
|
|
// Minimum weight of an edge. Please note, that weight is NEVER 0.
|
|
static const uint32_t MIN_WEIGHT = 1;
|
|
|
|
// Return TRUE if BB leads directly to a Return Instruction.
|
|
static bool isReturningBlock(BasicBlock *BB) {
|
|
SmallPtrSet<BasicBlock *, 8> Visited;
|
|
|
|
while (true) {
|
|
TerminatorInst *TI = BB->getTerminator();
|
|
if (isa<ReturnInst>(TI))
|
|
return true;
|
|
|
|
if (TI->getNumSuccessors() > 1)
|
|
break;
|
|
|
|
// It is unreachable block which we can consider as a return instruction.
|
|
if (TI->getNumSuccessors() == 0)
|
|
return true;
|
|
|
|
Visited.insert(BB);
|
|
BB = TI->getSuccessor(0);
|
|
|
|
// Stop if cycle is detected.
|
|
if (Visited.count(BB))
|
|
return false;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
// Multiply Edge Weight by two.
|
|
void incEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
|
|
uint32_t Weight = BP->getEdgeWeight(Src, Dst);
|
|
uint32_t MaxWeight = getMaxWeightFor(Src);
|
|
|
|
if (Weight * 2 > MaxWeight)
|
|
BP->setEdgeWeight(Src, Dst, MaxWeight);
|
|
else
|
|
BP->setEdgeWeight(Src, Dst, Weight * 2);
|
|
}
|
|
|
|
// Divide Edge Weight by two.
|
|
void decEdgeWeight(BasicBlock *Src, BasicBlock *Dst) {
|
|
uint32_t Weight = BP->getEdgeWeight(Src, Dst);
|
|
|
|
assert(Weight > 0);
|
|
if (Weight / 2 < MIN_WEIGHT)
|
|
BP->setEdgeWeight(Src, Dst, MIN_WEIGHT);
|
|
else
|
|
BP->setEdgeWeight(Src, Dst, Weight / 2);
|
|
}
|
|
|
|
|
|
uint32_t getMaxWeightFor(BasicBlock *BB) const {
|
|
return UINT32_MAX / BB->getTerminator()->getNumSuccessors();
|
|
}
|
|
|
|
public:
|
|
BranchProbabilityAnalysis(DenseMap<Edge, uint32_t> *W,
|
|
BranchProbabilityInfo *BP, LoopInfo *LI)
|
|
: Weights(W), BP(BP), LI(LI) {
|
|
}
|
|
|
|
// Return Heuristics
|
|
void calcReturnHeuristics(BasicBlock *BB);
|
|
|
|
// Pointer Heuristics
|
|
void calcPointerHeuristics(BasicBlock *BB);
|
|
|
|
// Loop Branch Heuristics
|
|
void calcLoopBranchHeuristics(BasicBlock *BB);
|
|
|
|
bool runOnFunction(Function &F);
|
|
};
|
|
|
|
// Calculate Edge Weights using "Return Heuristics". Predict a successor which
|
|
// leads directly to Return Instruction will not be taken.
|
|
void BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
|
|
if (BB->getTerminator()->getNumSuccessors() == 1)
|
|
return;
|
|
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
|
|
BasicBlock *Succ = *I;
|
|
if (isReturningBlock(Succ)) {
|
|
decEdgeWeight(BB, Succ);
|
|
}
|
|
}
|
|
}
|
|
|
|
// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
|
|
// between two pointer or pointer and NULL will fail.
|
|
void BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
|
|
BranchInst * BI = dyn_cast<BranchInst>(BB->getTerminator());
|
|
if (!BI || !BI->isConditional())
|
|
return;
|
|
|
|
Value *Cond = BI->getCondition();
|
|
ICmpInst *CI = dyn_cast<ICmpInst>(Cond);
|
|
if (!CI)
|
|
return;
|
|
|
|
Value *LHS = CI->getOperand(0);
|
|
|
|
if (!LHS->getType()->isPointerTy())
|
|
return;
|
|
|
|
assert(CI->getOperand(1)->getType()->isPointerTy());
|
|
|
|
BasicBlock *Taken = BI->getSuccessor(0);
|
|
BasicBlock *NonTaken = BI->getSuccessor(1);
|
|
|
|
// p != 0 -> isProb = true
|
|
// p == 0 -> isProb = false
|
|
// p != q -> isProb = true
|
|
// p == q -> isProb = false;
|
|
bool isProb = !CI->isEquality();
|
|
if (!isProb)
|
|
std::swap(Taken, NonTaken);
|
|
|
|
incEdgeWeight(BB, Taken);
|
|
decEdgeWeight(BB, NonTaken);
|
|
}
|
|
|
|
// Calculate Edge Weights using "Loop Branch Heuristics". Predict backedges
|
|
// as taken, exiting edges as not-taken.
|
|
void BranchProbabilityAnalysis::calcLoopBranchHeuristics(BasicBlock *BB) {
|
|
uint32_t numSuccs = BB->getTerminator()->getNumSuccessors();
|
|
|
|
Loop *L = LI->getLoopFor(BB);
|
|
if (!L)
|
|
return;
|
|
|
|
SmallVector<BasicBlock *, 8> BackEdges;
|
|
SmallVector<BasicBlock *, 8> ExitingEdges;
|
|
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
|
|
BasicBlock *Succ = *I;
|
|
Loop *SuccL = LI->getLoopFor(Succ);
|
|
if (SuccL != L)
|
|
ExitingEdges.push_back(Succ);
|
|
else if (Succ == L->getHeader())
|
|
BackEdges.push_back(Succ);
|
|
}
|
|
|
|
if (uint32_t numBackEdges = BackEdges.size()) {
|
|
uint32_t backWeight = LBH_TAKEN_WEIGHT / numBackEdges;
|
|
if (backWeight < NORMAL_WEIGHT)
|
|
backWeight = NORMAL_WEIGHT;
|
|
|
|
for (SmallVector<BasicBlock *, 8>::iterator EI = BackEdges.begin(),
|
|
EE = BackEdges.end(); EI != EE; ++EI) {
|
|
BasicBlock *Back = *EI;
|
|
BP->setEdgeWeight(BB, Back, backWeight);
|
|
}
|
|
}
|
|
|
|
uint32_t numExitingEdges = ExitingEdges.size();
|
|
if (uint32_t numNonExitingEdges = numSuccs - numExitingEdges) {
|
|
uint32_t exitWeight = LBH_NONTAKEN_WEIGHT / numNonExitingEdges;
|
|
if (exitWeight < MIN_WEIGHT)
|
|
exitWeight = MIN_WEIGHT;
|
|
|
|
for (SmallVector<BasicBlock *, 8>::iterator EI = ExitingEdges.begin(),
|
|
EE = ExitingEdges.end(); EI != EE; ++EI) {
|
|
BasicBlock *Exiting = *EI;
|
|
BP->setEdgeWeight(BB, Exiting, exitWeight);
|
|
}
|
|
}
|
|
}
|
|
|
|
bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
|
|
|
|
for (Function::iterator I = F.begin(), E = F.end(); I != E; ) {
|
|
BasicBlock *BB = I++;
|
|
|
|
// Only LBH uses setEdgeWeight method.
|
|
calcLoopBranchHeuristics(BB);
|
|
|
|
// PH and RH use only incEdgeWeight and decEwdgeWeight methods to
|
|
// not efface LBH results.
|
|
calcPointerHeuristics(BB);
|
|
calcReturnHeuristics(BB);
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
|
|
bool BranchProbabilityInfo::runOnFunction(Function &F) {
|
|
LoopInfo &LI = getAnalysis<LoopInfo>();
|
|
BranchProbabilityAnalysis BPA(&Weights, this, &LI);
|
|
return BPA.runOnFunction(F);
|
|
}
|
|
|
|
uint32_t BranchProbabilityInfo::getSumForBlock(BasicBlock *BB) const {
|
|
uint32_t Sum = 0;
|
|
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
|
|
BasicBlock *Succ = *I;
|
|
uint32_t Weight = getEdgeWeight(BB, Succ);
|
|
uint32_t PrevSum = Sum;
|
|
|
|
Sum += Weight;
|
|
assert(Sum > PrevSum); (void) PrevSum;
|
|
}
|
|
|
|
return Sum;
|
|
}
|
|
|
|
bool BranchProbabilityInfo::isEdgeHot(BasicBlock *Src, BasicBlock *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;
|
|
}
|
|
|
|
BasicBlock *BranchProbabilityInfo::getHotSucc(BasicBlock *BB) const {
|
|
uint32_t Sum = 0;
|
|
uint32_t MaxWeight = 0;
|
|
BasicBlock *MaxSucc = 0;
|
|
|
|
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
|
|
BasicBlock *Succ = *I;
|
|
uint32_t Weight = getEdgeWeight(BB, 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;
|
|
}
|
|
|
|
// Return edge's weight. If can't find it, return DEFAULT_WEIGHT value.
|
|
uint32_t
|
|
BranchProbabilityInfo::getEdgeWeight(BasicBlock *Src, BasicBlock *Dst) const {
|
|
Edge E(Src, Dst);
|
|
DenseMap<Edge, uint32_t>::const_iterator I = Weights.find(E);
|
|
|
|
if (I != Weights.end())
|
|
return I->second;
|
|
|
|
return DEFAULT_WEIGHT;
|
|
}
|
|
|
|
void BranchProbabilityInfo::setEdgeWeight(BasicBlock *Src, BasicBlock *Dst,
|
|
uint32_t Weight) {
|
|
Weights[std::make_pair(Src, Dst)] = Weight;
|
|
DEBUG(dbgs() << "set edge " << Src->getNameStr() << " -> "
|
|
<< Dst->getNameStr() << " weight to " << Weight
|
|
<< (isEdgeHot(Src, Dst) ? " [is HOT now]\n" : "\n"));
|
|
}
|
|
|
|
|
|
BranchProbability BranchProbabilityInfo::
|
|
getEdgeProbability(BasicBlock *Src, BasicBlock *Dst) const {
|
|
|
|
uint32_t N = getEdgeWeight(Src, Dst);
|
|
uint32_t D = getSumForBlock(Src);
|
|
|
|
return BranchProbability(N, D);
|
|
}
|
|
|
|
raw_ostream &
|
|
BranchProbabilityInfo::printEdgeProbability(raw_ostream &OS, BasicBlock *Src,
|
|
BasicBlock *Dst) const {
|
|
BranchProbability Prob = getEdgeProbability(Src, Dst);
|
|
|
|
OS << "edge " << Src->getNameStr() << " -> " << Dst->getNameStr()
|
|
<< " probability is " << Prob
|
|
<< (isEdgeHot(Src, Dst) ? " [HOT edge]\n" : "\n");
|
|
|
|
return OS;
|
|
}
|