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[ValueTracking] For NUW, X + Y are not 0 if they are nonequal #148101

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[ValueTracking] For NUW, X + Y are not 0 if they are nonequal #148101

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15 changes: 13 additions & 2 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2833,19 +2833,27 @@ static bool isNonZeroAdd(const APInt &DemandedElts, const SimplifyQuery &Q,
if (matchOpWithOpEqZero(X, Y))
return true;

if (NUW)
if (NUW) {
// X + Y != 0 if X != Y, and X + Y is NUW.
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A simpler way to state this:

Suggested change
// X + Y != 0 if X != Y, and X + Y is NUW.
// If X != Y then X +nuw Y != 0.

if (isKnownNonEqual(X, Y, DemandedElts, Q, Depth))
return true;
return isKnownNonZero(Y, DemandedElts, Q, Depth) ||
isKnownNonZero(X, DemandedElts, Q, Depth);
}

KnownBits XKnown = computeKnownBits(X, DemandedElts, Q, Depth);
KnownBits YKnown = computeKnownBits(Y, DemandedElts, Q, Depth);

// If X and Y are both non-negative (as signed values) then their sum is not
// zero unless both X and Y are zero.
if (XKnown.isNonNegative() && YKnown.isNonNegative())
if (XKnown.isNonNegative() && YKnown.isNonNegative()) {
if (isKnownNonZero(Y, DemandedElts, Q, Depth) ||
isKnownNonZero(X, DemandedElts, Q, Depth))
return true;
// X + Y != 0 if X != Y, and X + Y are both nonnegative.
if (isKnownNonEqual(X, Y, DemandedElts, Q, Depth))
return true;
}

// If X and Y are both negative (as signed values) then their sum is not
// zero unless both X and Y equal INT_MIN.
Expand All @@ -2859,6 +2867,9 @@ static bool isNonZeroAdd(const APInt &DemandedElts, const SimplifyQuery &Q,
// to INT_MIN.
if (YKnown.One.intersects(Mask))
return true;
// X + Y != 0 because if they are not equal, they cannot both be INT_MIN.
if (isKnownNonEqual(X, Y, DemandedElts, Q, Depth))
return true;
}

// The sum of a non-negative number and a power of two is not zero.
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