[patch, vectorizer] Fix PR tree-optimization/36293

[Richard Guenther]

On Thu, May 22, 2008 at 11:44 AM, Ira Rosen <IRAR@il.ibm.com> wrote:
>
> Hi,
>
> The fix of PR 36098
> (http://gcc.gnu.org/ml/gcc-patches/2008-05/msg00802.html) revealed a
> problem in generation of strided loads with gaps. When there is a gap in a
> group of strided loads, we load all the elements (including the gaps) and
> then skip the loads that correspond to the gaps (the redundant loads are
> later removed by DCE). There is no need to check if the first load must be
> skipped, since it cannot be a gap (we start a group of strided access only
> with actual data-ref). However, the check was O.K. since the value of gap
> for a first load of the group was always 0. The fix of PR 36098 stored a
> value different from 0 in DR_GROUP_GAP of a first load causing ICE.
>
> Bootstrapped with vectorization enabled and tested on ppc-linux. O.K. for
> 4.3.1 and trunk?

This is ok.

Thanks,
Richard.

> Thanks,
> Ira
>
> ChangeLog:
>
>      PR tree-optimization/36293
>      * tree-vect-transform.c (vect_transform_strided_load): Don't check
>      if the first load must be skipped because of a gap.
>
>
> Index: tree-vect-transform.c
> ===================================================================
> --- tree-vect-transform.c       (revision 135751)
> +++ tree-vect-transform.c       (working copy)
> @@ -5473,12 +5473,14 @@ vect_transform_strided_load (tree stmt,
>        break;
>
>       /* Skip the gaps. Loads created for the gaps will be removed by
> dead.
> -       code elimination pass later.
> +       code elimination pass later. No need to check for the first stmt
> in.
> +       the group, since it always exists.
>        DR_GROUP_GAP is the number of steps in elements from the previous
>        access (if there is no gap DR_GROUP_GAP is 1). We skip loads that
>        correspond to the gaps.
>       */
> -      if (gap_count < DR_GROUP_GAP (vinfo_for_stmt (next_stmt)))
> +      if (next_stmt != first_stmt
> +          && gap_count < DR_GROUP_GAP (vinfo_for_stmt (next_stmt)))
>       {
>         gap_count++;
>         continue;
>
>