diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp --- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp +++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp @@ -880,8 +880,15 @@ return SelectInst::Create(X, InstCombiner::SubOne(Op1C), Op1); // ~X + C --> (C-1) - X - if (match(Op0, m_Not(m_Value(X)))) - return BinaryOperator::CreateSub(InstCombiner::SubOne(Op1C), X); + if (match(Op0, m_Not(m_Value(X)))) { + // ~X + C has NSW and (C-1) won't oveflow => (C-1)-X can have NSW + auto *COne = ConstantInt::get(Op1C->getType(), 1); + bool WillNotSOV = willNotOverflowSignedSub(Op1C, COne, Add); + BinaryOperator *Res = + BinaryOperator::CreateSub(ConstantExpr::getSub(Op1C, COne), X); + Res->setHasNoSignedWrap(Add.hasNoSignedWrap() && WillNotSOV); + return Res; + } // (iN X s>> (N - 1)) + 1 --> zext (X > -1) const APInt *C; diff --git a/llvm/test/Transforms/InstCombine/add.ll b/llvm/test/Transforms/InstCombine/add.ll --- a/llvm/test/Transforms/InstCombine/add.ll +++ b/llvm/test/Transforms/InstCombine/add.ll @@ -360,7 +360,7 @@ ; ~X + -127 and (-128) - X with nsw are equally poisonous define i8 @test18_nsw(i8 %A) { ; CHECK-LABEL: @test18_nsw( -; CHECK-NEXT: [[C:%.*]] = sub i8 -128, [[A:%.*]] +; CHECK-NEXT: [[C:%.*]] = sub nsw i8 -128, [[A:%.*]] ; CHECK-NEXT: ret i8 [[C]] ; %B = xor i8 %A, -1 @@ -402,7 +402,7 @@ define <2 x i8> @test18vec_nsw(<2 x i8> %A) { ; CHECK-LABEL: @test18vec_nsw( -; CHECK-NEXT: [[C:%.*]] = sub <2 x i8> , [[A:%.*]] +; CHECK-NEXT: [[C:%.*]] = sub nsw <2 x i8> , [[A:%.*]] ; CHECK-NEXT: ret <2 x i8> [[C]] ; %B = xor <2 x i8> %A,