[Bug tree-optimization/37449] [4.4 Regression] calculix gets wrong answer for -O1 -ffast-math

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- 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