[Bug target/103771] [12 Regression] Missed vectorization under -mavx512f -mavx512vl after r12-5489

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103771

--- Comment #13 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 13 Jan 2022, rsandifo at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103771
> 
> --- Comment #9 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
> (In reply to Richard Biener from comment #7)
> > I think that is what we need to add.  We also don't have a good
> > representation
> > for "packing" of masks.
> > 
> > diff --git a/gcc/tree-vect-patterns.c b/gcc/tree-vect-patterns.c
> > index 3ea905538e1..729a1d32612 100644
> > --- a/gcc/tree-vect-patterns.c
> > +++ b/gcc/tree-vect-patterns.c
> > @@ -4679,8 +4679,10 @@ vect_recog_mask_conversion_pattern (vec_info *vinfo,
> >                                   rhs1_type);
> >         }
> >  
> > -      if (maybe_ne (TYPE_VECTOR_SUBPARTS (vectype1),
> > -                   TYPE_VECTOR_SUBPARTS (vectype2)))
> > +      /* AVX512 style masks cannot be packed/unpacked.  */
> > +      if (TYPE_PRECISION (TREE_TYPE (vectype2)) != 1
> > +         && maybe_ne (TYPE_VECTOR_SUBPARTS (vectype1),
> > +                      TYPE_VECTOR_SUBPARTS (vectype2)))
> >         tmp = build_mask_conversion (vinfo, rhs1, vectype1, stmt_vinfo);
> >        else
> >         tmp = rhs1;
> Haven't had time to look at it properly yet, but my first impression
> is that that's likely to regress SVE.  Packing and unpacking are
> natural operations on boolean vector modes.

Sure, but we can't produce scalar code mimicking this for
1 bit element vectors.  It "works" for the others because based
on the width of the elements we choose a vector with different
number of elements.  But here the pattern produces a 8 bit element
which isn't want is desired here.