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[InstCombine] Propagate nsw in (sub (and Op1, (neg X)), Op1) --> neg (and Op1, (add X, -1)) #149366

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[InstCombine] Propagate nsw in (sub (and Op1, (neg X)), Op1) --> neg (and Op1, (add X, -1)) #149366

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23 changes: 19 additions & 4 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2588,10 +2588,25 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
{
// (sub (and Op1, (neg X)), Op1) --> neg (and Op1, (add X, -1))
Value *X;
if (match(Op0, m_OneUse(m_c_And(m_Specific(Op1),
m_OneUse(m_Neg(m_Value(X))))))) {
return BinaryOperator::CreateNeg(Builder.CreateAnd(
Op1, Builder.CreateAdd(X, Constant::getAllOnesValue(I.getType()))));
BinaryOperator *NegInst;
if (match(Op0,
m_OneUse(m_c_And(m_Specific(Op1), m_OneUse(m_BinOp(NegInst))))) &&
match(NegInst, m_Neg(m_Value(X)))) {

// If neg X is nsw, then X - 1 must be too
bool AddHasNSW = NegInst->hasNoSignedWrap();

// If the original sub is nsw, then the final neg must be too
bool NegHasNSW = I.hasNoSignedWrap();

Value *Add =
Builder.CreateAdd(X, Constant::getAllOnesValue(I.getType()), "",
/*HasNUW=*/false, /*HasNSW=*/AddHasNSW);
Value *And = Builder.CreateAnd(Op1, Add);

// Use CreateNSWNeg or CreateNeg based on the flag
return NegHasNSW ? BinaryOperator::CreateNSWNeg(And)
: BinaryOperator::CreateNeg(And);
}
}

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39 changes: 39 additions & 0 deletions llvm/test/Transforms/InstCombine/hoist-negation-out-of-bias-calculation.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,45 @@ define i8 @t0(i8 %x, i8 %y) {
ret i8 %negbias
}

define i8 @t0_nsw(i8 %x, i8 %y) {
; CHECK-LABEL: @t0_nsw(
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = and i8 [[X:%.*]], [[TMP1]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub i8 0, [[TMP2]]
; CHECK-NEXT: ret i8 [[NEGBIAS]]
;
%negy = sub nsw i8 0, %y
%unbiasedx = and i8 %negy, %x
%negbias = sub i8 %unbiasedx, %x
ret i8 %negbias
}

define i8 @t0_nsw_2(i8 %x, i8 %y) {
; CHECK-LABEL: @t0_nsw_2(
; CHECK-NEXT: [[TMP1:%.*]] = add i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = and i8 [[X:%.*]], [[TMP1]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub nsw i8 0, [[TMP2]]
; CHECK-NEXT: ret i8 [[NEGBIAS]]
;
%negy = sub i8 0, %y
%unbiasedx = and i8 %negy, %x
%negbias = sub nsw i8 %unbiasedx, %x
ret i8 %negbias
}

define i8 @t0_nsw_3(i8 %x, i8 %y) {
; CHECK-LABEL: @t0_nsw_3(
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = and i8 [[X:%.*]], [[TMP1]]
; CHECK-NEXT: [[NEGBIAS:%.*]] = sub nsw i8 0, [[TMP2]]
; CHECK-NEXT: ret i8 [[NEGBIAS]]
;
%negy = sub nsw i8 0, %y
%unbiasedx = and i8 %negy, %x
%negbias = sub nsw i8 %unbiasedx, %x
ret i8 %negbias
}

declare i8 @gen8()

define i8 @t1_commutative(i8 %y) {
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