The fmin/fmax tests added by D95245 use the no-nans-fp-math function
attribute, and fail to vectorize when the attribute is removed in favour of using
nnan directly in the instructions. This patch changes isRecurrenceInstr
to also check if the no-NaNs flag is set on the fcmp/select.
I'm not sure if there are any problems with this approach, which is why I've
split this out from D95245.