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PGO: preserve branch-weight metadata when simplifying two branches with a common

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destination in SimplifyCondBranchToCondBranch.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164054 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Manman Ren 2012-09-17 21:30:40 +00:00
parent ff1547890a
commit 566540332f
2 changed files with 49 additions and 1 deletions
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27
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2150,6 +2150,33 @@ static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
PBI->setSuccessor(0, CommonDest);
PBI->setSuccessor(1, OtherDest);
// Update branch weight for PBI.
uint64_t PredTrueWeight, PredFalseWeight, SuccTrueWeight, SuccFalseWeight;
bool PredHasWeights = ExtractBranchMetadata(PBI, PredTrueWeight,
PredFalseWeight);
bool SuccHasWeights = ExtractBranchMetadata(BI, SuccTrueWeight,
SuccFalseWeight);
if (PredHasWeights && SuccHasWeights) {
uint64_t PredCommon = PBIOp ? PredFalseWeight : PredTrueWeight;
uint64_t PredOther = PBIOp ?PredTrueWeight : PredFalseWeight;
uint64_t SuccCommon = BIOp ? SuccFalseWeight : SuccTrueWeight;
uint64_t SuccOther = BIOp ? SuccTrueWeight : SuccFalseWeight;
// The weight to CommonDest should be PredCommon * SuccTotal +
// PredOther * SuccCommon.
// The weight to OtherDest should be PredOther * SuccOther.
SmallVector<uint64_t, 2> NewWeights;
NewWeights.push_back(PredCommon * (SuccCommon + SuccOther) +
PredOther * SuccCommon);
NewWeights.push_back(PredOther * SuccOther);
// Halve the weights if any of them cannot fit in an uint32_t
FitWeights(NewWeights);
SmallVector<uint32_t, 2> MDWeights(NewWeights.begin(),NewWeights.end());
PBI->setMetadata(LLVMContext::MD_prof,
MDBuilder(BI->getContext()).
createBranchWeights(MDWeights));
}
// OtherDest may have phi nodes. If so, add an entry from PBI's
// block that are identical to the entries for BI's block.
AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);

23
test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -174,16 +174,37 @@ Z:
ret void
}
define void @test7(i1 %a, i1 %b) {
; CHECK: @test7
entry:
%c = or i1 %b, false
br i1 %a, label %Y, label %X, !prof !0
; CHECK: br i1 %brmerge, label %Y, label %Z, !prof !5
X:
br i1 %c, label %Y, label %Z, !prof !6
Y:
call void @helper(i32 0)
ret void
Z:
call void @helper(i32 1)
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}
!4 = metadata !{metadata !"branch_weights", i32 4, i32 3, i32 2, i32 1}
!5 = metadata !{metadata !"branch_weights", i32 7, i32 6, i32 5}
!6 = metadata !{metadata !"branch_weights", i32 1, i32 3}
; CHECK: !0 = metadata !{metadata !"branch_weights", i32 5, i32 11}
; CHECK: !1 = metadata !{metadata !"branch_weights", i32 1, i32 5}
; CHECK: !2 = metadata !{metadata !"branch_weights", i32 7, i32 1, i32 2}
; CHECK: !3 = metadata !{metadata !"branch_weights", i32 49, i32 12, i32 24, i32 35}
; CHECK: !4 = metadata !{metadata !"branch_weights", i32 11, i32 5}
; CHECK-NOT: !5
; CHECK: !5 = metadata !{metadata !"branch_weights", i32 17, i32 15}
; CHECK-NOT: !6