[RFC] Fix PR28684

[Paul Brook]

> >    associate:
> >      /* In most languages, can't associate operations on floats through
> >         parentheses.  Rather than remember where the parentheses were, we
> >         don't associate floats at all, unless the user has specified
> >         -funsafe-math-optimizations.  */
>
> Ah, interesting.  As a numerical guy, the "reorder unless in paranthesis"
> is certainly what I'm used to, but I figured it was the hassle of keeping
> track of it that kept you guys from implementing . . .

That's because you're used to programming in Fortran. No such rule exists in 
C. gfortran doesn't currently take advantage of that particular fortran 
feature, but that's a largely separate issue.

Paul