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Don't use isNullValue to evaluate ConstantExpr

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ConstantExpr can evaluate to false even when isNullValue gives false.

Fixes PR18143.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196611 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan P. N. Exon Smith 2013-12-06 21:48:36 +00:00
parent 92b10e5f85
commit 42883d0ac4
2 changed files with 23 additions and 1 deletions
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5
lib/Transforms/InstCombine/InstructionCombining.cpp
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@ -699,7 +699,10 @@ Instruction *InstCombiner::FoldOpIntoPhi(Instruction &I) {
Value *TrueVInPred = TrueV->DoPHITranslation(PhiTransBB, ThisBB);
Value *FalseVInPred = FalseV->DoPHITranslation(PhiTransBB, ThisBB);
Value *InV = 0;
if (Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i)))
// Beware of ConstantExpr: it may eventually evaluate to getNullValue,
// even if currently isNullValue gives false.
Constant *InC = dyn_cast<Constant>(PN->getIncomingValue(i));
if (InC && !isa<ConstantExpr>(InC))
InV = InC->isNullValue() ? FalseVInPred : TrueVInPred;
else
InV = Builder->CreateSelect(PN->getIncomingValue(i),

19
test/Transforms/InstCombine/phi-select-constexpr.ll Normal file
View File

@ -0,0 +1,19 @@
; RUN: opt < %s -S -instcombine | FileCheck %s
@A = extern_weak global i32, align 4
@B = extern_weak global i32, align 4
define i32 @foo(i1 %which) {
entry:
br i1 %which, label %final, label %delay
delay:
br label %final
; CHECK-LABEL: final:
; CHECK: phi i32 [ 1, %entry ], [ select (i1 icmp eq (i32* @A, i32* @B), i32 2, i32 1), %delay ]
final:
%use2 = phi i1 [ false, %entry ], [ icmp eq (i32* @A, i32* @B), %delay ]
%value = select i1 %use2, i32 2, i32 1
ret i32 %value
}