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[InstCombine] Propagate NSW in ~((-X) | Y) --> (X - 1) & (~Y) #149359

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[InstCombine] Propagate NSW in ~((-X) | Y) --> (X - 1) & (~Y) #149359

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641ae74
Pre-commit test (NFC)
AZero13 Jul 17, 2025
a8e39c2
Propagate NSW in ~((-X) | Y) --> (X - 1) & (~Y)
AZero13 Jul 17, 2025
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14 changes: 14 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4750,8 +4750,22 @@ Instruction *InstCombinerImpl::foldNot(BinaryOperator &I) {
BinaryOperator *NotVal;
if (match(NotOp, m_BinOp(NotVal))) {
// ~((-X) | Y) --> (X - 1) & (~Y)
if (match(NotVal,
m_OneUse(m_c_Or(m_OneUse(m_NSWNeg(m_Value(X))), m_Value(Y))))) {
// If -X is nsw, then X - 1 must be too.
// This is because -X can only be nsw if X is any number that is not
// INT_MIN. And if X is not INT_MIN, then X - 1 must be nsw.
Value *DecX = Builder.CreateAdd(X, ConstantInt::getAllOnesValue(Ty), "",
/*HasNUW=*/false, /*HasNSW=*/true);
Value *NotY = Builder.CreateNot(Y);
return BinaryOperator::CreateAnd(DecX, NotY);
}

if (match(NotVal,
m_OneUse(m_c_Or(m_OneUse(m_Neg(m_Value(X))), m_Value(Y))))) {
// If -X is nsw, then X - 1 must be too.
// This is because -X can only be nsw if X is any number that is not
// INT_MIN. And if X is not INT_MIN, then X - 1 must be nsw.
Value *DecX = Builder.CreateAdd(X, ConstantInt::getAllOnesValue(Ty));
Value *NotY = Builder.CreateNot(Y);
return BinaryOperator::CreateAnd(DecX, NotY);
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28 changes: 28 additions & 0 deletions llvm/test/Transforms/InstCombine/not.ll
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Expand Up @@ -436,6 +436,34 @@ define <3 x i5> @not_or_neg_commute_vec(<3 x i5> %x, <3 x i5> %p) {
ret <3 x i5> %not
}

define i8 @not_or_neg_nsw(i8 %x, i8 %y) {
; CHECK-LABEL: @not_or_neg_nsw(
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i8 [[Y:%.*]], -1
; CHECK-NEXT: [[TMP2:%.*]] = xor i8 [[X:%.*]], -1
; CHECK-NEXT: [[NOT:%.*]] = and i8 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i8 [[NOT]]
;
%s = sub nsw i8 0, %y
%o = or i8 %s, %x
%not = xor i8 %o, -1
ret i8 %not
}

define <3 x i5> @not_or_neg_commute_vec_nsw(<3 x i5> %x, <3 x i5> %p) {
; CHECK-LABEL: @not_or_neg_commute_vec_nsw(
; CHECK-NEXT: [[Y:%.*]] = mul <3 x i5> [[P:%.*]], <i5 1, i5 2, i5 3>
; CHECK-NEXT: [[TMP1:%.*]] = add nsw <3 x i5> [[X:%.*]], splat (i5 -1)
; CHECK-NEXT: [[TMP2:%.*]] = xor <3 x i5> [[Y]], splat (i5 -1)
; CHECK-NEXT: [[NOT:%.*]] = and <3 x i5> [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret <3 x i5> [[NOT]]
;
%y = mul <3 x i5> %p, <i5 1, i5 2, i5 3> ; thwart complexity-based-canonicalization
%s = sub nsw <3 x i5> <i5 0, i5 0, i5 poison>, %x
%o = or <3 x i5> %y, %s
%not = xor <3 x i5> %o, <i5 -1, i5 poison, i5 -1>
ret <3 x i5> %not
}

; negative test

define i8 @not_or_neg_use1(i8 %x, i8 %y) {
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