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[InstCombine] Don't transform sub X, ~Y -> add X, -Y unless Y is actually negatable #72767

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[InstCombine] Don't transform sub X, ~Y -> add X, -Y unless Y is actually negatable #72767

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82f0e80
[InstCombine] Add tests for improving `sub X, ~Y` -> `add X, -Y`; NFC
goldsteinn Nov 18, 2023
bea9aeb
[InstCombine] Don't transform `sub X, ~Y` -> `add X, -Y` unless `Y` i…
goldsteinn Nov 18, 2023
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8 changes: 5 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp
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Expand Up @@ -447,9 +447,11 @@ std::array<Value *, 2> Negator::getSortedOperandsOfBinOp(Instruction *I) {
// `xor` is negatible if one of its operands is invertible.
// FIXME: InstCombineInverter? But how to connect Inverter and Negator?
if (auto *C = dyn_cast<Constant>(Ops[1])) {
Value *Xor = Builder.CreateXor(Ops[0], ConstantExpr::getNot(C));
return Builder.CreateAdd(Xor, ConstantInt::get(Xor->getType(), 1),
I->getName() + ".neg");
if (IsTrulyNegation) {
Value *Xor = Builder.CreateXor(Ops[0], ConstantExpr::getNot(C));
return Builder.CreateAdd(Xor, ConstantInt::get(Xor->getType(), 1),
I->getName() + ".neg");
}
}
return nullptr;
}
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5 changes: 2 additions & 3 deletions llvm/test/Analysis/ValueTracking/knownbits-and-or-xor-lowbit.ll
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Expand Up @@ -106,9 +106,8 @@ define <2 x i1> @sub_XY_and_bit0_is_zero_fail(<2 x i8> %x, <2 x i8> %C) nounwind

define i1 @sub_XY_xor_bit0_is_one_fail(i8 %x, i8 %C) nounwind {
; CHECK-LABEL: @sub_XY_xor_bit0_is_one_fail(
; CHECK-NEXT: [[TMP1:%.*]] = xor i8 [[C:%.*]], -2
; CHECK-NEXT: [[C1_NEG:%.*]] = add i8 [[TMP1]], 1
; CHECK-NEXT: [[Y:%.*]] = add i8 [[C1_NEG]], [[X:%.*]]
; CHECK-NEXT: [[C1:%.*]] = xor i8 [[C:%.*]], 1
; CHECK-NEXT: [[Y:%.*]] = sub i8 [[X:%.*]], [[C1]]
; CHECK-NEXT: [[W:%.*]] = xor i8 [[Y]], [[X]]
; CHECK-NEXT: [[R:%.*]] = icmp eq i8 [[W]], 10
; CHECK-NEXT: ret i1 [[R]]
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27 changes: 20 additions & 7 deletions llvm/test/Transforms/InstCombine/fold-sub-of-not-to-inc-of-add.ll
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Expand Up @@ -22,6 +22,19 @@ define i32 @p0_scalar(i32 %x, i32 %y) {
ret i32 %t1
}

define i8 @p0_scalar_not_truly_negatable(i8 %x, i8 %y) {
; CHECK-LABEL: @p0_scalar_not_truly_negatable(
; CHECK-NEXT: [[XX:%.*]] = xor i8 [[X:%.*]], 123
; CHECK-NEXT: [[YY:%.*]] = xor i8 [[Y:%.*]], 45
; CHECK-NEXT: [[R:%.*]] = sub i8 [[XX]], [[YY]]
; CHECK-NEXT: ret i8 [[R]]
;
%xx = xor i8 %x, 123
%yy = xor i8 %y, 45
%r = sub i8 %xx, %yy
ret i8 %r
}

;------------------------------------------------------------------------------;
; Vector tests
;------------------------------------------------------------------------------;
Expand Down Expand Up @@ -79,28 +92,28 @@ define i32 @n4(i32 %x, i32 %y) {
; CHECK-NEXT: ret i32 [[T1]]
;
%t0 = xor i32 %x, -1
%t1 = sub i32 %t0, %y ; swapped
%t1 = sub i32 %t0, %y ; swapped
ret i32 %t1
}

define i32 @n5_is_not_not(i32 %x, i32 %y) {
; CHECK-LABEL: @n5_is_not_not(
; CHECK-NEXT: [[T0_NEG:%.*]] = add i32 [[X:%.*]], -2147483647
; CHECK-NEXT: [[T1:%.*]] = add i32 [[T0_NEG]], [[Y:%.*]]
; CHECK-NEXT: [[T0:%.*]] = xor i32 [[X:%.*]], 2147483647
; CHECK-NEXT: [[T1:%.*]] = sub i32 [[Y:%.*]], [[T0]]
; CHECK-NEXT: ret i32 [[T1]]
;
%t0 = xor i32 %x, 2147483647 ; not -1
%t0 = xor i32 %x, 2147483647 ; not -1
%t1 = sub i32 %y, %t0
ret i32 %t1
}

define <2 x i32> @n5_is_not_not_vec_splat(<2 x i32> %x, <2 x i32> %y) {
; CHECK-LABEL: @n5_is_not_not_vec_splat(
; CHECK-NEXT: [[T0_NEG:%.*]] = add <2 x i32> [[X:%.*]], <i32 -2147483647, i32 -2147483647>
; CHECK-NEXT: [[T1:%.*]] = add <2 x i32> [[T0_NEG]], [[Y:%.*]]
; CHECK-NEXT: [[T0:%.*]] = xor <2 x i32> [[X:%.*]], <i32 2147483647, i32 2147483647>
; CHECK-NEXT: [[T1:%.*]] = sub <2 x i32> [[Y:%.*]], [[T0]]
; CHECK-NEXT: ret <2 x i32> [[T1]]
;
%t0 = xor <2 x i32> %x, <i32 2147483647, i32 2147483647> ; signmask, but not -1
%t0 = xor <2 x i32> %x, <i32 2147483647, i32 2147483647> ; signmask, but not -1
%t1 = sub <2 x i32> %y, %t0
ret <2 x i32> %t1
}