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[ConstantFolding] Fixing addo/subo with undef 

When folding addo/subo with undef, the current
convention is to use { -1, false } for addo and
{ 0, false } for subo. This was fixed for InstSimplify in
https://reviews.llvm.org/rGf094d65beaa492e845b03561eddd75b5be653a01,
but not in ConstantFolding.

Reviewed By: nikic, lebedev.ri

Differential Revision: https://reviews.llvm.org/D99564
This commit is contained in:
George Mitenkov 2021-03-31 21:46:28 +03:00
parent 10847f6217
commit 807b019ca2
2 changed files with 12 additions and 9 deletions
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13
llvm/lib/Analysis/ConstantFolding.cpp
View File

@ -2519,16 +2519,19 @@ static Constant *ConstantFoldScalarCall2(StringRef Name,
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:
// X - undef -> { 0, false }
// undef - X -> { 0, false }
if (!C0 || !C1)
return Constant::getNullValue(Ty);
LLVM_FALLTHROUGH;
case Intrinsic::uadd_with_overflow:
case Intrinsic::sadd_with_overflow:
// X - undef -> { undef, false }
// undef - X -> { undef, false }
// X + undef -> { undef, false }
// undef + x -> { undef, false }
// X + undef -> { -1, false }
// undef + x -> { -1, false }
if (!C0 || !C1) {
return ConstantStruct::get(
cast<StructType>(Ty),
{UndefValue::get(Ty->getStructElementType(0)),
{Constant::getAllOnesValue(Ty->getStructElementType(0)),
Constant::getNullValue(Ty->getStructElementType(1))});
}
LLVM_FALLTHROUGH;

8
llvm/test/Transforms/InstSimplify/ConstProp/overflow-ops.ll
View File

@ -31,7 +31,7 @@ define {i8, i1} @uadd_2() nounwind {
define {i8, i1} @uadd_undef() nounwind {
; CHECK-LABEL: @uadd_undef(
; CHECK-NEXT: ret { i8, i1 } { i8 undef, i1 false }
; CHECK-NEXT: ret { i8, i1 } { i8 -1, i1 false }
;
%t = call {i8, i1} @llvm.uadd.with.overflow.i8(i8 142, i8 undef)
ret {i8, i1} %t
@ -59,7 +59,7 @@ define {i8, i1} @usub_2() nounwind {
define {i8, i1} @usub_undef() nounwind {
; CHECK-LABEL: @usub_undef(
; CHECK-NEXT: ret { i8, i1 } { i8 undef, i1 false }
; CHECK-NEXT: ret { i8, i1 } zeroinitializer
;
%t = call {i8, i1} @llvm.usub.with.overflow.i8(i8 4, i8 undef)
ret {i8, i1} %t
@ -147,7 +147,7 @@ define {i8, i1} @sadd_5() nounwind {
define {i8, i1} @sadd_undef() nounwind {
; CHECK-LABEL: @sadd_undef(
; CHECK-NEXT: ret { i8, i1 } { i8 undef, i1 false }
; CHECK-NEXT: ret { i8, i1 } { i8 -1, i1 false }
;
%t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 undef, i8 -10)
ret {i8, i1} %t
@ -215,7 +215,7 @@ define {i8, i1} @ssub_5() nounwind {
define {i8, i1} @ssub_undef() nounwind {
; CHECK-LABEL: @ssub_undef(
; CHECK-NEXT: ret { i8, i1 } { i8 undef, i1 false }
; CHECK-NEXT: ret { i8, i1 } zeroinitializer
;
%t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 undef, i8 -10)
ret {i8, i1} %t