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ComputeMaskedBits: sub falls through to add, and sub doesn't have the same overflow semantics as add.

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Should fix the selfhost failures that started with r127463.

llvm-svn: 127465
This commit is contained in:
Benjamin Kramer 2011-03-11 14:46:49 +00:00
parent 666407939f
commit d4ea449e7e
2 changed files with 12 additions and 1 deletions
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3
lib/Analysis/ValueTracking.cpp
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@ -431,7 +431,8 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask,
}
// Are we still trying to solve for the sign bit?
if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){
if (I->getOpcode() == Instruction::Add &&
Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){
OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(I);
if (OBO->hasNoSignedWrap()) {
// Adding two positive numbers can't wrap into negative ...

10
test/Transforms/InstCombine/sext.ll
View File

@ -126,3 +126,13 @@ define void @test11(<2 x i16> %srcA, <2 x i16> %srcB, <2 x i16>* %dst) {
; CHECK-NEXT: store <2 x i16>
; CHECK-NEXT: ret
}
define i64 @test12(i32 %x) nounwind {
%shr = lshr i32 %x, 1
%sub = sub nsw i32 0, %shr
%conv = sext i32 %sub to i64
ret i64 %conv
; CHECK: @test12
; CHECK: sext
; CHECK: ret
}