Currently InstructionSimplify.cpp knows how to simplify floating point instructions that have a NaN operand. It does not know how to handle the matching constrained FP intrinsic.
This patch teaches it how to simplify so long as the exception handling is not "fpexcept.strict".
Does it make sense to pass rounding mode instead of IsDefaultFPEnv and deduce if environment is default inside the function? Could it be useful for other foldings?