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[KnownBits] Add force{Non}Negative API #110389

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[KnownBits] Add force{Non}Negative API #110389

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14 changes: 14 additions & 0 deletions llvm/include/llvm/Support/KnownBits.h
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Original file line number Diff line number Diff line change
Expand Up @@ -114,6 +114,20 @@ struct KnownBits {
Zero.setSignBit();
}

/// Force this value to be negative. Unlike `makeNegative`, this will clear
/// any existing signbit.
void forceNegative() {
Zero.clearSignBit();
One.setSignBit();
}

/// Force this value to be non-negative. Unlike `makeNonNegative`, this will
/// clear any existing signbit.
void forceNonNegative() {
One.clearSignBit();
Zero.setSignBit();
}

/// Return the minimal unsigned value possible given these KnownBits.
APInt getMinValue() const {
// Assume that all bits that aren't known-ones are zeros.
Expand Down
32 changes: 11 additions & 21 deletions llvm/lib/Support/KnownBits.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -578,8 +578,7 @@ KnownBits KnownBits::abs(bool IntMinIsPoison) const {
// is poison anyways.
if (IntMinIsPoison && Tmp.countMinPopulation() == 1 &&
Tmp.countMaxPopulation() != 1) {
Tmp.One.clearSignBit();
Tmp.Zero.setSignBit();
Tmp.forceNonNegative();
KnownAbs.One.setBits(getBitWidth() - Tmp.countMinLeadingZeros(),
getBitWidth() - 1);
}
Expand All @@ -596,10 +595,8 @@ KnownBits KnownBits::abs(bool IntMinIsPoison) const {
// We only know that the absolute values's MSB will be zero if INT_MIN is
// poison, or there is a set bit that isn't the sign bit (otherwise it could
// be INT_MIN).
if (IntMinIsPoison || (!One.isZero() && !One.isMinSignedValue())) {
KnownAbs.One.clearSignBit();
KnownAbs.Zero.setSignBit();
}
if (IntMinIsPoison || (!One.isZero() && !One.isMinSignedValue()))
KnownAbs.forceNonNegative();
}

return KnownAbs;
Expand Down Expand Up @@ -658,26 +655,19 @@ static KnownBits computeForSatAddSub(bool Add, bool Signed,

if (Signed) {
if (Add) {
if (LHS.isNonNegative() && RHS.isNonNegative()) {
if (LHS.isNonNegative() && RHS.isNonNegative())
// Pos + Pos -> Pos
Res.One.clearSignBit();
Res.Zero.setSignBit();
}
if (LHS.isNegative() && RHS.isNegative()) {
Res.forceNonNegative();
if (LHS.isNegative() && RHS.isNegative())
// Neg + Neg -> Neg
Res.One.setSignBit();
Res.Zero.clearSignBit();
}
Res.forceNegative();
} else {
if (LHS.isNegative() && RHS.isNonNegative()) {
if (LHS.isNegative() && RHS.isNonNegative())
// Neg - Pos -> Neg
Res.One.setSignBit();
Res.Zero.clearSignBit();
} else if (LHS.isNonNegative() && RHS.isNegative()) {
Res.forceNegative();
else if (LHS.isNonNegative() && RHS.isNegative())
// Pos - Neg -> Pos
Res.One.clearSignBit();
Res.Zero.setSignBit();
}
Res.forceNonNegative();
}
} else {
// Add: Leading ones of either operand are preserved.
Expand Down
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