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InstCombine: Don't just copy known bits from the first operand of an srem.

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That's obviously wrong. Conservatively restrict it to the sign bit, which
matches the original intention of this analysis. Fixes PR15940.

llvm-svn: 181518
This commit is contained in:
Benjamin Kramer 2013-05-09 16:32:32 +00:00
parent 2e056f9798
commit 54122b8028
2 changed files with 13 additions and 1 deletions
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2
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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@ -754,7 +754,7 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
// If it's known zero, our sign bit is also zero.
if (LHSKnownZero.isNegative())
KnownZero |= LHSKnownZero;
KnownZero.setBit(KnownZero.getBitWidth() - 1);
}
break;
case Instruction::URem: {

12
test/Transforms/InstCombine/icmp.ll
View File

@ -707,6 +707,18 @@ define i1 @test69(i32 %c) nounwind uwtable {
ret i1 %3
}
; PR15940
; CHECK: @test70
; CHECK-NEXT: %A = srem i32 5, %X
; CHECK-NEXT: %C = icmp ne i32 %A, 2
; CHECK-NEXT: ret i1 %C
define i1 @test70(i32 %X) {
%A = srem i32 5, %X
%B = add i32 %A, 2
%C = icmp ne i32 %B, 4
ret i1 %C
}
; CHECK: @icmp_sext16trunc
; CHECK-NEXT: %1 = trunc i32 %x to i16
; CHECK-NEXT: %cmp = icmp slt i16 %1, 36