[Bug tree-optimization/32183] -fast-math causes a missed optimization to happen

[hjl at lucon dot org]

------- Comment #5 from hjl at lucon dot org  2007-06-02 00:10 -------
(In reply to comment #3)
> (In reply to comment #2)
> > Is that OK to transform
> > 
> >       float sf;
> >       ...
> >       sf = 500 * sf;
> >       for (i = 0; i < ceplen; i++)
> >         sum[i] *= sf;
> > 
> > to
> > 
> >       for (i = 0; i < ceplen; i++)
> >         sum[i] = (sum[i]* 500)*sf;
> > 
> > You can certainly get the different results when sf is small and sum[i] is
> > large.
> 
> with -ffast-math, this transformation is ok (although it does not seem to make
> sense to do it, it moves a multiplication into a loop).
>

We moved a multiply, which is outside of loop in source, into
a loop. I don't think gcc should do it with any optimization
flag, including -ffast-math.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32183