https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63743
--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Zhenqiang Chen from comment #2)
> (In reply to Jakub Jelinek from comment #1)
> > Were we swapping operands before? I mean, if you rewrite the testcase to
> > swap the * arguments in the source, did you get the same more efficient code
> > in the past?
>
> Yes. I tried the test case:
>
> double
> test1 (double x, double y)
> {
> return x * (x + y);
> }
> double
> test2 (double x, double y)
> {
> return (x + y) * x;
> }
>
> Without r216728, I got efficient codes for both functions. But with r216728,
> I got inefficient codes for both functions.
What about
double
test3 (double x, double y)
{
return (x + y) * (x - y);
}
? At least from quick looking at ppc -msoft-float -O2 -m32, I see the same
issue there, add called first, sub called second, and result of second returned
in the same registers as used for the first argument. So something to handle at
expansion or RA rather than in GIMPLE anyway IMHO.
