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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
View File

@ -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);

34
test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -79,10 +79,42 @@ Z:
ret void
}
;; test5 - The case where it jumps to the default target will be removed.
define void @test5(i32 %M, i32 %N) nounwind uwtable {
entry:
switch i32 %N, label %sw2 [
i32 1, label %sw2
i32 2, label %sw.bb
i32 3, label %sw.bb1
], !prof !3
; CHECK: test5
; CHECK: switch i32 %N, label %sw2 [
; CHECK: i32 3, label %sw.bb1
; CHECK: i32 2, label %sw.bb
; CHECK: ], !prof !2
sw.bb:
call void @helper(i32 0)
br label %sw.epilog
sw.bb1:
call void @helper(i32 1)
br label %sw.epilog
sw2:
call void @helper(i32 2)
br label %sw.epilog
sw.epilog:
ret void
}
!0 = metadata !{metadata !"branch_weights", i32 3, i32 5}
!1 = metadata !{metadata !"branch_weights", i32 1, i32 1}
!2 = metadata !{metadata !"branch_weights", i32 1, i32 2}
!3 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
; CHECK-NOT: !2
; CHECK: !2 = metadata !{metadata !"branch_weights", i32 7, i32 1, i32 2}
; CHECK-NOT: !3