PGO: preserve branch-weight metadata when simplifying Switch to a sub, an icmp
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
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 1316b85..3365c2f 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -2853,9 +2853,28 @@
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 @@
}
}
+ 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();
}