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Now that we have comparison on probabilities, add some static functions 

to get important constant branch probabilities and use them for finding
the best branch out of a set of possibilities.

llvm-svn: 142762
This commit is contained in:
Chandler Carruth 2011-10-23 20:10:34 +00:00
parent 446210b616
commit fd7475e906
2 changed files with 8 additions and 8 deletions
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3
llvm/include/llvm/Support/BranchProbability.h
View File

@ -39,6 +39,9 @@ public:
assert(n <= d && "Probability cannot be bigger than 1!"); assert(n <= d && "Probability cannot be bigger than 1!");
} }
static BranchProbability getZero() { return BranchProbability(0, 1); }
static BranchProbability getOne() { return BranchProbability(1, 1); }
uint32_t getNumerator() const { return N; } uint32_t getNumerator() const { return N; }
uint32_t getDenominator() const { return D; } uint32_t getDenominator() const { return D; }

13
llvm/lib/CodeGen/MachineBlockPlacement.cpp
View File

@ -287,10 +287,8 @@ void MachineBlockPlacement::mergeSuccessor(MachineBasicBlock *BB,
return; return;
// Walk through the successors looking for the highest probability edge. // Walk through the successors looking for the highest probability edge.
// FIXME: This is an annoying way to do the comparison, but it's correct.
// Support should be added to BranchProbability to properly compare two.
MachineBasicBlock *Successor = 0; MachineBasicBlock *Successor = 0;
BlockFrequency BestFreq; BranchProbability BestProb = BranchProbability::getZero();
DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n"); DEBUG(dbgs() << "Attempting merge from: " << getBlockName(BB) << "\n");
for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(), for (MachineBasicBlock::succ_iterator SI = BB->succ_begin(),
SE = BB->succ_end(); SE = BB->succ_end();
@ -298,13 +296,12 @@ void MachineBlockPlacement::mergeSuccessor(MachineBasicBlock *BB,
if (BB == *SI || (Filter && !Filter->count(*SI))) if (BB == *SI || (Filter && !Filter->count(*SI)))
continue; continue;
BlockFrequency SuccFreq(BlockFrequency::getEntryFrequency()); BranchProbability SuccProb = MBPI->getEdgeProbability(BB, *SI);
SuccFreq *= MBPI->getEdgeProbability(BB, *SI); DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccProb << "\n");
DEBUG(dbgs() << " " << getBlockName(*SI) << " -> " << SuccFreq << "\n"); if (!Successor || SuccProb > BestProb || (!(SuccProb < BestProb) &&
if (!Successor || SuccFreq > BestFreq || (!(SuccFreq < BestFreq) &&
BB->isLayoutSuccessor(*SI))) { BB->isLayoutSuccessor(*SI))) {
Successor = *SI; Successor = *SI;
BestFreq = SuccFreq; BestProb = SuccProb;
} }
} }
if (!Successor) if (!Successor)