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PGO: preserve branch-weight metadata when simplifying Switch to a sub, an icmp

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and a conditional branch; also when removing dead cases from a switch.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164084 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
2012-09-18 00:47:33 +00:00
parent e4095f95ac
commit 222d6192ad
2 changed files with 85 additions and 2 deletions
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39
lib/Transforms/Utils/SimplifyCFG.cpp
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@ -2853,9 +2853,28 @@ static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
if (!Offset->isNullValue())
Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
Builder.CreateCondBr(
BranchInst *NewBI = Builder.CreateCondBr(
Cmp, SI->case_begin().getCaseSuccessor(), SI->getDefaultDest());
// Update weight for the newly-created conditional branch.
SmallVector<uint64_t, 8> Weights;
bool HasWeights = HasBranchWeights(SI);
if (HasWeights) {
GetBranchWeights(SI, Weights);
if (Weights.size() == 1 + SI->getNumCases()) {
// Combine all weights for the cases to be the true weight of NewBI.
// We assume that the sum of all weights for a Terminator can fit into 32
// bits.
uint32_t NewTrueWeight = 0;
for (unsigned I = 1, E = Weights.size(); I != E; ++I)
NewTrueWeight += (uint32_t)Weights[I];
NewBI->setMetadata(LLVMContext::MD_prof,
MDBuilder(SI->getContext()).
createBranchWeights(NewTrueWeight,
(uint32_t)Weights[0]));
}
}
// Prune obsolete incoming values off the successor's PHI nodes.
for (BasicBlock::iterator BBI = SI->case_begin().getCaseSuccessor()->begin();
isa<PHINode>(BBI); ++BBI) {
@ -2886,15 +2905,33 @@ static bool EliminateDeadSwitchCases(SwitchInst *SI) {
}
}
SmallVector<uint64_t, 8> Weights;
bool HasWeight = HasBranchWeights(SI);
if (HasWeight) {
GetBranchWeights(SI, Weights);
HasWeight = (Weights.size() == 1 + SI->getNumCases());
}
// Remove dead cases from the switch.
for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
SwitchInst::CaseIt Case = SI->findCaseValue(DeadCases[I]);
assert(Case != SI->case_default() &&
"Case was not found. Probably mistake in DeadCases forming.");
if (HasWeight) {
std::swap(Weights[Case.getCaseIndex()+1], Weights.back());
Weights.pop_back();
}
// Prune unused values from PHI nodes.
Case.getCaseSuccessor()->removePredecessor(SI->getParent());
SI->removeCase(Case);
}
if (HasWeight) {
SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
SI->setMetadata(LLVMContext::MD_prof,
MDBuilder(SI->getParent()->getContext()).
createBranchWeights(MDWeights));
}
return !DeadCases.empty();
}