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BranchProbabilityInfo: floating point equality is unlikely. 

This is from the same paper from Ball and Larus as the rest of the currently implemented heuristics.

llvm-svn: 142677
This commit is contained in:
Benjamin Kramer 2011-10-21 20:12:47 +00:00
parent 99904b33b7
commit 1e731a10d0
1 changed files with 34 additions and 2 deletions
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36
llvm/lib/Analysis/BranchProbabilityInfo.cpp
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@ -76,6 +76,9 @@ class BranchProbabilityAnalysis {
static const uint32_t ZH_TAKEN_WEIGHT = 20;
static const uint32_t ZH_NONTAKEN_WEIGHT = 12;
static const uint32_t FPH_TAKEN_WEIGHT = 20;
static const uint32_t FPH_NONTAKEN_WEIGHT = 12;
// Standard weight value. Used when none of the heuristics set weight for
// the edge.
static const uint32_t NORMAL_WEIGHT = 16;
@ -131,9 +134,12 @@ public:
// Loop Branch Heuristics
bool calcLoopBranchHeuristics(BasicBlock *BB);
// Zero Heurestics
// Zero Heuristics
bool calcZeroHeuristics(BasicBlock *BB);
// Floating Point Heuristics
bool calcFloatingPointHeuristics(BasicBlock *BB);
bool runOnFunction(Function &F);
};
} // end anonymous namespace
@ -378,6 +384,29 @@ bool BranchProbabilityAnalysis::calcZeroHeuristics(BasicBlock *BB) {
return true;
}
bool BranchProbabilityAnalysis::calcFloatingPointHeuristics(BasicBlock *BB) {
BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator());
if (!BI || !BI->isConditional())
return false;
Value *Cond = BI->getCondition();
FCmpInst *FCmp = dyn_cast<FCmpInst>(Cond);
if (!FCmp || !FCmp->isEquality())
return false;
BasicBlock *Taken = BI->getSuccessor(0);
BasicBlock *NonTaken = BI->getSuccessor(1);
// f1 == f2 -> Unlikely
// f1 != f2 -> Likely
if (FCmp->isTrueWhenEqual())
std::swap(Taken, NonTaken);
BP->setEdgeWeight(BB, Taken, FPH_TAKEN_WEIGHT);
BP->setEdgeWeight(BB, NonTaken, FPH_NONTAKEN_WEIGHT);
return true;
}
bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
@ -396,7 +425,10 @@ bool BranchProbabilityAnalysis::runOnFunction(Function &F) {
if (calcPointerHeuristics(BB))
continue;
calcZeroHeuristics(BB);
if (calcZeroHeuristics(BB))
continue;
calcFloatingPointHeuristics(BB);
}
return false;