[Bug fortran/42131] Weird translation of DO loops

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

------- Comment #17 from rguenther at suse dot de  2009-11-27 09:47 -------
Subject: Re:  Weird translation of DO loops

On Thu, 26 Nov 2009, tkoenig at gcc dot gnu dot org wrote:

> ------- Comment #13 from tkoenig at gcc dot gnu dot org  2009-11-26 21:56 -------
> Created an attachment (id=19159)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19159&action=view)
>  --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=19159&action=view)
> patch that implements the multiplication idea
> 
> This generates
> 
>    if (D.1339 > 0)
>       {
>         if (D.1338 < D.1337)
>           {
>             goto L.2;
>           }
>         else
>           {
>             step_sign.2 = 1;
>           }
>       }
>     else
>       {
>         if (D.1338 > D.1337)
>           {
>             goto L.2;
>           }
>         else
>           {
>             step_sign.2 = -1;
>           }
>       }
>     countm1.1 = (((character(kind=4)) D.1338 - (character(kind=4)) D.1337) *
> (character(kind=4)) step_sign.2) / (character(kind=4)) (step_sign.2 * D.1339);
> 
> implementing the multiplication idea outlined above, and passes at
> least do_3.F90.
> 
> Better?

Unfortunately the conditional step_sign.2 is as bad as a conditional
countm1.1 for optimization.  The above might even be worse than
the original.

Richard.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42131