PGO: preserve branch-weight metadata when simplifying a switch with a single
case to a conditional branch and when removing dead cases.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163942 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 551df00..a9d74cd 100644
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -667,13 +667,32 @@
DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
<< "Through successor TI: " << *TI);
+ // Collect branch weights into a vector.
+ SmallVector<uint32_t, 8> Weights;
+ MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
+ bool HasWeight = MD && (MD->getNumOperands() == 2 + SI->getNumCases());
+ if (HasWeight)
+ for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
+ ++MD_i) {
+ ConstantInt* CI = dyn_cast<ConstantInt>(MD->getOperand(MD_i));
+ assert(CI);
+ Weights.push_back(CI->getValue().getZExtValue());
+ }
for (SwitchInst::CaseIt i = SI->case_end(), e = SI->case_begin(); i != e;) {
--i;
if (DeadCases.count(i.getCaseValue())) {
+ if (HasWeight) {
+ std::swap(Weights[i.getCaseIndex()+1], Weights.back());
+ Weights.pop_back();
+ }
i.getCaseSuccessor()->removePredecessor(TI->getParent());
SI->removeCase(i);
}
}
+ if (HasWeight)
+ SI->setMetadata(LLVMContext::MD_prof,
+ MDBuilder(SI->getParent()->getContext()).
+ createBranchWeights(Weights));
DEBUG(dbgs() << "Leaving: " << *TI << "\n");
return true;