================
@@ -5805,6 +5805,37 @@ void computeKnownFPClass(const Value *V, const APInt
&DemandedElts,
break;
}
+ case Instruction::BitCast: {
+ const Value *Src;
+ if (!match(Op, m_ElementWiseBitCast(m_Value(Src))) ||
+ !Src->getType()->isIntOrIntVectorTy())
+ break;
+
+ const Type *Ty = Op->getType()->getScalarType();
+ KnownBits Bits(Ty->getScalarSizeInBits());
+ computeKnownBits(Src, DemandedElts, Bits, Depth + 1, Q);
+
+ // Transfer information from the sign bit.
+ if (Bits.isNonNegative())
+ Known.signBitMustBeZero();
+ else if (Bits.isNegative())
+ Known.signBitMustBeOne();
+
+ if (Ty->isIEEE()) {
+ // IEEE floats are NaN when all bits of the exponent plus at least one of
+ // the fraction bits are 1. This means:
+ // - If we assume unknown bits are 0 and the value is NaN, it will
+ // always be NaN
+ // - If we assume unknown bits are 1 and the value is not NaN, it can
+ // never be NaN
+ if (APFloat(Ty->getFltSemantics(), Bits.One).isNaN())
+ Known.KnownFPClasses = fcNan;
+ else if (!APFloat(Ty->getFltSemantics(), ~Bits.Zero).isNaN())
+ Known.knownNot(fcNan);
----------------
arsenm wrote:
inf is simpler, but normal / subnormal would require knowing at least one bit
of the mantissa is set and the exponent is not the maximum which is trickier
https://github.com/llvm/llvm-project/pull/97762
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