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[ValueTracking] improve isKnownNonZero precision for smax #88170

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[ValueTracking] improve isKnownNonZero precision for smax #88170

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d5966f8
[ValueTracking] Add tests for improving `isKnownNonZero` of `smax`; NFC
goldsteinn Apr 9, 2024
0454763
[ValueTracking] improve `isKnownNonZero` precision for `smax`
goldsteinn Apr 9, 2024
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41 changes: 31 additions & 10 deletions llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2828,23 +2828,44 @@ static bool isKnownNonZeroFromOperator(const Operator *I,
case Intrinsic::uadd_sat:
return isKnownNonZero(II->getArgOperand(1), DemandedElts, Depth, Q) ||
isKnownNonZero(II->getArgOperand(0), DemandedElts, Depth, Q);
case Intrinsic::smin:
case Intrinsic::smax: {
auto KnownOpImpliesNonZero = [&](const KnownBits &K) {
return II->getIntrinsicID() == Intrinsic::smin
? K.isNegative()
: K.isStrictlyPositive();
// If either arg is strictly positive the result is non-zero. Otherwise
// the result is non-zero if both ops are non-zero.
auto IsNonZero = [&](Value *Op, std::optional<bool> &OpNonZero,
KnownBits OpKnown) {
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Suggested change
KnownBits OpKnown) {
const KnownBits &OpKnown) {

if (!OpNonZero.has_value())
OpNonZero = OpKnown.isNonZero() ||
isKnownNonZero(Op, DemandedElts, Depth, Q);
return *OpNonZero;
};
KnownBits XKnown =
// Avoid re-computing isKnownNonZero.
std::optional<bool> Op0NonZero, Op1NonZero;
KnownBits Op1Known =
computeKnownBits(II->getArgOperand(1), DemandedElts, Depth, Q);
if (Op1Known.isNonNegative() &&
IsNonZero(II->getArgOperand(1), Op1NonZero, Op1Known))
return true;
KnownBits Op0Known =
computeKnownBits(II->getArgOperand(0), DemandedElts, Depth, Q);
if (KnownOpImpliesNonZero(XKnown))
if (Op0Known.isNonNegative() &&
IsNonZero(II->getArgOperand(0), Op0NonZero, Op0Known))
return true;
KnownBits YKnown =
return IsNonZero(II->getArgOperand(1), Op1NonZero, Op1Known) &&
IsNonZero(II->getArgOperand(0), Op0NonZero, Op0Known);
}
case Intrinsic::smin: {
// If either arg is negative the result is non-zero. Otherwise
// the result is non-zero if both ops are non-zero.
KnownBits Op1Known =
computeKnownBits(II->getArgOperand(1), DemandedElts, Depth, Q);
if (KnownOpImpliesNonZero(YKnown))
if (Op1Known.isNegative())
return true;
KnownBits Op0Known =
computeKnownBits(II->getArgOperand(0), DemandedElts, Depth, Q);
if (Op0Known.isNegative())
return true;

if (XKnown.isNonZero() && YKnown.isNonZero())
if (Op1Known.isNonZero() && Op0Known.isNonZero())
return true;
}
[[fallthrough]];
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11 changes: 11 additions & 0 deletions llvm/test/Transforms/InstSimplify/known-non-zero.ll
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Expand Up @@ -166,3 +166,14 @@ A:
B:
ret i1 0
}

define i1 @smax_non_zero(i8 %xx, i8 %y) {
; CHECK-LABEL: @smax_non_zero(
; CHECK-NEXT: ret i1 false
;
%x0 = and i8 %xx, 63
%x = add i8 %x0, 1
%v = call i8 @llvm.smax.i8(i8 %x, i8 %y)
%r = icmp eq i8 %v, 0
ret i1 %r
}