Commit f112e469 authored by Noah Goldstein's avatar Noah Goldstein
Browse files

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

This combine was previously adding instruction in some cases (see the
tests).

Closes #72767
parent 3af514e5

llvm/lib/Transforms/InstCombine/InstCombineNegator.cpp

+5 −3
Original line number Diff line number Diff line
@@ -447,10 +447,12 @@ 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])) {

      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;

  }

  case Instruction::Mul: {

llvm/test/Analysis/ValueTracking/knownbits-and-or-xor-lowbit.ll

+2 −3
Original line number Diff line number Diff line
@@ -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]]

llvm/test/Transforms/InstCombine/fold-sub-of-not-to-inc-of-add.ll

+6 −7
Original line number Diff line number Diff line
@@ -25,9 +25,8 @@ define i32 @p0_scalar(i32 %x, i32 %y) { 
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:    [[TMP1:%.*]] = xor i8 [[Y:%.*]], -46

; CHECK-NEXT:    [[YY_NEG:%.*]] = add i8 [[TMP1]], 1

; CHECK-NEXT:    [[R:%.*]] = add i8 [[YY_NEG]], [[XX]]

; CHECK-NEXT:    [[YY:%.*]] = xor i8 [[Y:%.*]], 45

; CHECK-NEXT:    [[R:%.*]] = sub i8 [[XX]], [[YY]]

; CHECK-NEXT:    ret i8 [[R]]

;

  %xx = xor i8 %x, 123
@@ -99,8 +98,8 @@ define i32 @n4(i32 %x, i32 %y) { 


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
@@ -110,8 +109,8 @@ define i32 @n5_is_not_not(i32 %x, i32 %y) { 


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