Optimisation prevents overflow?

[Davide Mancusi]

Brooks Moses wrote:
> Paul Brook has corrected me.  The extra-precision registers _do_ have
> enough extra precision that 273 is a reasonable answer for this theory.
> 
> Sorry for the confusion, then.  :)
> 
> So, yeah, -ffloat-store or -mfpmath=sse is the right answer.

This brings me to a "philosophical" question, then. Say that program
"foo" gives different results depending on the use of -ffloat-store; I
am not talking about round-off here, I mean real differences. Would you
say that "foo" is not portable? In other words, relying on overflow (or
underflow) is obviously not portable, but is overflow the _only_ way to
trigger inconsistent behaviours?

Davide