------- Comment #22 from rguenther at suse dot de 2008-10-15 18:33 -------
Subject: Re: [4.4 Regression] calculix gets
wrong answer for -O1 -ffast-math
On Wed, 15 Oct 2008, dberlin at dberlin dot org wrote:
> ------- Comment #21 from dberlin at gcc dot gnu dot org 2008-10-15 17:55
> -------
> Subject: Re: [4.4 Regression] calculix gets wrong answer for -O1 -ffast-math
>
> >
> > It already does (I fixed that recently), but we only phi-translate during
> > insertion and we
> > don't insert for that case, as obviously there is no partial redundancy.
>
> True, but if it discovered all the new phi arguments would be constant
> it used to create a new phi node with the new constant values and let
> eliminate replace the old calculation with the new phi node.
>
> Maybe it only did this if all the constants ended up the same value,
> but it would be trivial to do it if all the arguments are constant,
> regardless of whether they are the same value.
> :)
Well, we already do for
int foo (int b)
{
double i;
if (b)
i = 4;
else
i = 9;
return __builtin_sqrt(i);
}
<bb 4>:
# i_1 = PHI <4.0e+0(5), 9.0e+0(3)>
# prephitmp.11_7 = PHI <2.0e+0(5), 3.0e+0(3)>
# prephitmp.12_8 = PHI <2(5), 3(3)>
D.1238_5 = prephitmp.11_7;
D.1237_6 = prephitmp.12_8;
return D.1237_6;
at least. Somebody needs to look why it doesn't happen for the
testcase posted.
Richard.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37449
