Ideally the normal fadd/fmin/fmax this was creating would fail the verifier.
It's probably also necessary to force off FP exception handlers in the cmpxchg
loop but we don't have a generic way to do that now.
Note strictfp builder is broken in the minnum/maxnum case
I'd reword: "If FP exceptions are observable".
And, FTR, GCC does already do this (and it's required by the spec). So we should actually fix that at some point. :)