[Bug tree-optimization/107346] [13 Regression] gnat.dg/loop_optimization23_pkg.ad failure afer r13-3413-ge10ca9544632db

["ebotcazou at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107346

Eric Botcazou <ebotcazou at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ebotcazou at gcc dot gnu.org

--- Comment #8 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
> I am wondering whether I should try to support this, or bail out of
> vect_check_gather_scatter if pbitpos is not a multiple of BITS_PER_UNIT. The
> latter obviously feels safer.

It turns out that this vect_check_gather_scatter problem was latent since I can
reproduce it with the GCC 12 compiler in Ada, and the following fix:

diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
index e32b1779c5d..a22eb2d763d 100644
--- a/gcc/tree-vect-data-refs.cc
+++ b/gcc/tree-vect-data-refs.cc
@@ -4013,7 +4013,7 @@ vect_check_gather_scatter (stmt_vec_info stmt_info,
loop_vec_info loop_vinfo,
      that can be gimplified before the loop.  */
   base = get_inner_reference (base, &pbitsize, &pbitpos, &off, &pmode,
                              &punsignedp, &reversep, &pvolatilep);
-  if (reversep)
+  if (!multiple_p (pbitpos, BITS_PER_UNIT) || reversep)
     return false;

   poly_int64 pbytepos = exact_div (pbitpos, BITS_PER_UNIT);

is sufficient to get rid of it.