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Remove incEdgeWeight and decEdgeWeight. Set edge weight directly to avoid 

rounding errors.

llvm-svn: 136456
This commit is contained in:
Jakub Staszak 2011-07-29 02:36:53 +00:00
parent bc836c2c84
commit 0978426843
1 changed files with 35 additions and 30 deletions
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65
llvm/lib/Analysis/BranchProbabilityInfo.cpp
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@ -66,6 +66,12 @@ class BranchProbabilityAnalysis {
static const uint32_t LBH_TAKEN_WEIGHT = 124;
static const uint32_t LBH_NONTAKEN_WEIGHT = 4;
static const uint32_t RH_TAKEN_WEIGHT = 24;
static const uint32_t RH_NONTAKEN_WEIGHT = 8;
static const uint32_t PH_TAKEN_WEIGHT = 20;
static const uint32_t PH_NONTAKEN_WEIGHT = 12;
// Standard weight value. Used when none of the heuristics set weight for
// the edge.
static const uint32_t NORMAL_WEIGHT = 16;
@ -100,29 +106,6 @@ class BranchProbabilityAnalysis {
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();
}
@ -152,16 +135,38 @@ bool BranchProbabilityAnalysis::calcReturnHeuristics(BasicBlock *BB){
if (BB->getTerminator()->getNumSuccessors() == 1)
return false;
bool Any = false;
SmallVector<BasicBlock *, 4> ReturningEdges;
SmallVector<BasicBlock *, 4> StayEdges;
for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
BasicBlock *Succ = *I;
if (isReturningBlock(Succ)) {
decEdgeWeight(BB, Succ);
Any = true;
if (isReturningBlock(Succ))
ReturningEdges.push_back(Succ);
else
StayEdges.push_back(Succ);
}
if (uint32_t numStayEdges = StayEdges.size()) {
uint32_t stayWeight = RH_TAKEN_WEIGHT / numStayEdges;
if (stayWeight < NORMAL_WEIGHT)
stayWeight = NORMAL_WEIGHT;
for (SmallVector<BasicBlock *, 4>::iterator I = StayEdges.begin(),
E = StayEdges.end(); I != E; ++I)
BP->setEdgeWeight(BB, *I, stayWeight);
}
if (uint32_t numRetEdges = ReturningEdges.size()) {
uint32_t retWeight = RH_NONTAKEN_WEIGHT / numRetEdges;
if (retWeight < MIN_WEIGHT)
retWeight = MIN_WEIGHT;
for (SmallVector<BasicBlock *, 4>::iterator I = ReturningEdges.begin(),
E = ReturningEdges.end(); I != E; ++I) {
BP->setEdgeWeight(BB, *I, retWeight);
}
}
return Any;
return ReturningEdges.size() > 0;
}
// Calculate Edge Weights using "Pointer Heuristics". Predict a comparsion
@ -194,8 +199,8 @@ bool BranchProbabilityAnalysis::calcPointerHeuristics(BasicBlock *BB) {
if (!isProb)
std::swap(Taken, NonTaken);
incEdgeWeight(BB, Taken);
decEdgeWeight(BB, NonTaken);
BP->setEdgeWeight(BB, Taken, PH_TAKEN_WEIGHT);
BP->setEdgeWeight(BB, NonTaken, PH_NONTAKEN_WEIGHT);
return true;
}