https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31873
Eric Gallager <egallager at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |dberlin at gcc dot gnu.org,
| |kazu at codesourcery dot com,
| |roger at eyesopen dot com
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=25125
--- Comment #3 from Eric Gallager <egallager at gcc dot gnu.org> ---
(In reply to Dorit Naishlos from comment #0)
> This PR was originally opened against PRE (PR25809), but turns out PRE can't
> solve this problem, so here's a new PR instead:
>
> In testcases that have reduction, like gcc.dg/vect/vect-reduc-2char.c and
> gcc.dg/vect-reduc-2short.c, the following casts appear:
>
> signed char sdiff;
> unsigned char ux, udiff;
> sdiff_0 = ...
> loop:
> # sdiff_41 = PHI <sdiff_39, sdiff_0>;
> .....
> ux_36 = ....
> udiff_37 = (unsigned char) sdiff_41;
> udiff_38 = x_36 + udiff_37;
> sdiff_39 = (signed char) udiff_38;
> end_loop
>
> although these casts could be taken out of loop all together. i.e., transform
> the code into something like the following:
>
> signed char sdiff;
> unsigned char ux, udiff;
> sdiff_0 = ...
> udiff_1 = (unsigned char) sdiff_0;
> loop:
> # udiff_3 = PHI <udiff_2, udiff_1>;
> .....
> ux_36 = ....
> udiff_2 = ux_36 + udiff_3;
> end_loop
> sdiff_39 = (signed char) udiff_2;
>
> see this discussion thread:
> http://gcc.gnu.org/ml/gcc-patches/2005-12/msg01827.html
thread says this is related to bug 25125; adding that under "See Also"
(also adding some people from the thread on cc)
