[InstCombine] Don't add fcmp instructions to strictfp functions (#81498)

The strictfp attribute has the requirement that "LLVM will not introduce
any new floating-point instructions that may trap". The llvm.is.fpclass
intrinsic is documented as "The function never raises floating-point
exceptions", and the fcmp instruction may raise one, so we can't
transform the former into the latter in functions with the strictfp
attribute.

Author: ostannard

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -902,7 +902,8 @@ Instruction *InstCombinerImpl::foldIntrinsicIsFPClass(IntrinsicInst &II) {
   const FPClassTest OrderedMask = Mask & ~fcNan;
   const FPClassTest OrderedInvertedMask = ~OrderedMask & ~fcNan;
 
-  const bool IsStrict = II.isStrictFP();
+  const bool IsStrict =
+      II.getFunction()->getAttributes().hasFnAttr(Attribute::StrictFP);
 
   Value *FNegSrc;
   if (match(Src0, m_FNeg(m_Value(FNegSrc)))) {