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[InstSimplify] Fix addo/subo undef folds (PR42209)

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Fix folds of addo and subo with an undef operand to be:

`@llvm.{u,s}{add,sub}.with.overflow` all fold to `{ undef, false }`,
 as per LLVM undef rules.
Same for commuted variants.

Based on the original version of the patch by @nikic.

Fixes [[ https://bugs.llvm.org/show_bug.cgi?id=42209 | PR42209 ]]

Differential Revision: https://reviews.llvm.org/D63065

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@363522 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Roman Lebedev
2019-06-16 20:39:45 +00:00
parent e51018c229
commit d09f140cd1
3 changed files with 20 additions and 16 deletions
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lib/Analysis/InstructionSimplify.cpp
+11 -8
View File
@@ -4843,16 +4843,19 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
// X - X -> { 0, false }
if (Op0 == Op1)
return Constant::getNullValue(ReturnType);
// X - undef -> undef
// undef - X -> undef
if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
return UndefValue::get(ReturnType);
break;
LLVM_FALLTHROUGH;
case Intrinsic::uadd_with_overflow:
case Intrinsic::sadd_with_overflow:
// X + undef -> undef
if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1))
return UndefValue::get(ReturnType);
// X - undef -> { undef, false }
// undef - X -> { undef, false }
// X + undef -> { undef, false }
// undef + x -> { undef, false }
if (isa<UndefValue>(Op0) || isa<UndefValue>(Op1)) {
return ConstantStruct::get(
cast<StructType>(ReturnType),
{UndefValue::get(ReturnType->getStructElementType(0)),
Constant::getNullValue(ReturnType->getStructElementType(1))});
}
break;
case Intrinsic::umul_with_overflow:
case Intrinsic::smul_with_overflow: