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Merging r214385:

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r214385 | majnemer | 2014-07-30 21:49:29 -0700 (Wed, 30 Jul 2014) | 9 lines

InstCombine: Correctly propagate NSW/NUW for x-(-A) -> x+A

We can only propagate the nsw bits if both subtraction instructions are
marked with the appropriate bit.

N.B.  We only propagate the nsw bit in InstCombine because the nuw case
is already handled in InstSimplify.

This fixes PR20189.
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_35@223644 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-12-08 09:11:36 +00:00
parent f38406688d
commit af44f02444
2 changed files with 18 additions and 3 deletions
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12
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@ -1462,11 +1462,17 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (Value *V = SimplifyUsingDistributiveLaws(I))
return ReplaceInstUsesWith(I, V);
// If this is a 'B = x-(-A)', change to B = x+A. This preserves NSW/NUW.
// If this is a 'B = x-(-A)', change to B = x+A.
if (Value *V = dyn_castNegVal(Op1)) {
BinaryOperator *Res = BinaryOperator::CreateAdd(Op0, V);
Res->setHasNoSignedWrap(I.hasNoSignedWrap());
Res->setHasNoUnsignedWrap(I.hasNoUnsignedWrap());
if (const auto *BO = dyn_cast<BinaryOperator>(Op1)) {
assert(BO->getOpcode() == Instruction::Sub &&
"Expected a subtraction operator!");
if (BO->hasNoSignedWrap() && I.hasNoSignedWrap())
Res->setHasNoSignedWrap(true);
}
return Res;
}

9
test/Transforms/InstCombine/sub.ll
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@ -464,3 +464,12 @@ define i32 @test38(i32 %A) {
; CHECK-NEXT: [[SEXT:%.*]] = sext i1 [[ICMP]] to i32
; CHECK-NEXT: ret i32 [[SEXT]]
}
define i32 @test39(i32 %A, i32 %x) {
%B = sub i32 0, %A
%C = sub nsw i32 %x, %B
ret i32 %C
; CHECK-LABEL: @test39(
; CHECK: %C = add i32 %x, %A
; CHECK: ret i32 %C
}