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PGO: preserve branch-weight metadata when simplifying Switch

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Hanlde the case when we split the default edge if the default target has "icmp"
and unconditinal branch.

llvm-svn: 164076
This commit is contained in:
Manman Ren 2012-09-17 23:07:43 +00:00
parent 1956ad7efe
commit 77511d5a11
2 changed files with 51 additions and 1 deletions
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15
lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2425,6 +2425,21 @@ static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
// the switch to the merge point on the compared value.
BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
BB->getParent(), BB);
SmallVector<uint64_t, 8> Weights;
bool HasWeights = HasBranchWeights(SI);
if (HasWeights) {
GetBranchWeights(SI, Weights);
if (Weights.size() == 1 + SI->getNumCases()) {
// Split weight for default case to case for "Cst".
Weights[0] = (Weights[0]+1) >> 1;
Weights.push_back(Weights[0]);
SmallVector<uint32_t, 8> MDWeights(Weights.begin(), Weights.end());
SI->setMetadata(LLVMContext::MD_prof,
MDBuilder(SI->getContext()).
createBranchWeights(MDWeights));
}
}
SI->addCase(Cst, NewBB);
// NewBB branches to the phi block, add the uncond branch and the phi entry.

37
test/Transforms/SimplifyCFG/preserve-branchweights.ll
View File

@ -216,6 +216,40 @@ bees:
ret void
}
; Test edge splitting when the default target has icmp and unconditinal
; branch
define i1 @test9(i32 %x, i32 %y) nounwind {
; CHECK: @test9
entry:
switch i32 %x, label %bees [
i32 0, label %a
i32 1, label %end
i32 2, label %end
], !prof !7
; CHECK: switch i32 %x, label %bees [
; CHECK: i32 0, label %a
; CHECK: i32 1, label %end
; CHECK: i32 2, label %end
; CHECK: i32 92, label %end
; CHECK: ], !prof !7
a:
call void @helper(i32 0) nounwind
%reta = icmp slt i32 %x, %y
ret i1 %reta
bees:
%tmp = icmp eq i32 %x, 92
br label %end
end:
; CHECK: end:
; CHECK: %ret = phi i1 [ true, %entry ], [ false, %bees ], [ true, %entry ], [ true, %entry ]
%ret = phi i1 [ true, %entry ], [%tmp, %bees], [true, %entry]
call void @helper(i32 2) nounwind
ret i1 %ret
}
!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}
@ -232,4 +266,5 @@ bees:
; CHECK: !4 = metadata !{metadata !"branch_weights", i32 11, i32 5}
; CHECK: !5 = metadata !{metadata !"branch_weights", i32 17, i32 15}
; CHECK: !6 = metadata !{metadata !"branch_weights", i32 9, i32 7}
; CHECK-NOT: !7
; CHECK: !7 = metadata !{metadata !"branch_weights", i32 17, i32 9, i32 8, i32 7, i32 17}
; CHECK-NOT: !8