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PGO: preserve branch-weight metadata when removing a case which jumps

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to the default target.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163724 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren
2012-09-12 17:04:11 +00:00
parent 67c8978617
commit ee99c7f1bf
2 changed files with 55 additions and 1 deletions
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22
lib/Transforms/Utils/Local.cpp
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@@ -23,6 +23,7 @@
#include "llvm/Instructions.h"
#include "llvm/IntrinsicInst.h"
#include "llvm/Intrinsics.h"
#include "llvm/MDBuilder.h"
#include "llvm/Metadata.h"
#include "llvm/Operator.h"
#include "llvm/ADT/DenseMap.h"
@@ -122,6 +123,27 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
// Check to see if this branch is going to the same place as the default
// dest. If so, eliminate it as an explicit compare.
if (i.getCaseSuccessor() == DefaultDest) {
MDNode* MD = SI->getMetadata(LLVMContext::MD_prof);
// MD should have 2 + NumCases operands.
if (MD && MD->getNumOperands() == 2 + SI->getNumCases()) {
// Collect branch weights into a vector.
SmallVector<uint32_t, 8> Weights;
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());
}
// Merge weight of this case to the default weight.
unsigned idx = i.getCaseIndex();
Weights[0] += Weights[idx+1];
// Remove weight for this case.
std::swap(Weights[idx+1], Weights.back());
Weights.pop_back();
SI->setMetadata(LLVMContext::MD_prof,
MDBuilder(BB->getContext()).
createBranchWeights(Weights));
}
// Remove this entry.
DefaultDest->removePredecessor(SI->getParent());
SI->removeCase(i);