On Thu, 10 Jul 2025, Tamar Christina wrote:
> > -----Original Message-----
> > From: Richard Biener <rguent...@suse.de>
> > Sent: Thursday, July 10, 2025 1:31 PM
> > To: gcc-patches@gcc.gnu.org
> > Cc: Richard Sandiford <richard.sandif...@arm.com>; Tamar Christina
> > <tamar.christ...@arm.com>; RISC-V CI <patchworks...@rivosinc.com>
> > Subject: [PATCH] Reject single lane vector types for SLP build
> >
> > The following makes us never consider vector(1) T types for
> > vectorization and ensures this during SLP build. This is a
> > long-standing issue for BB vectorization and when we remove
> > early loop vector type setting we lose the single place we have
> > that rejects this for loops.
> >
> > Once we implement partial loop vectorization we should revisit
> > this, but then use the original scalar types for the unvectorized
> > parts.
>
> SGTM FWIW,
>
> I was also wondering if I should start upstreaming my changes to
> get the vectorizer to recognize vector types as scalar types as well.
>
> Or if you wanted me to wait until I have the lane representations
> more figured out.
I think if we can restrict things to cases that have a strong
overlap with what we intend to use in the end that sounds good.
Like allow only a single "scalar" vector def per SLP node for now
and simply stash that into the scalar-stmts array. In the end
we'd want to allow mixed scalar and vector defs there.
It does require altering code that expects to get at actual _scalar_
defs for each lane, but I don't think that's much code.
Richard.
> Regards,
> Tamar
> >
> > Bootstrapped and tested on x86_64-unknown-linux-gnu. I'll see
> > if there's any surprises from the CI, but otherwise I'll go
> > ahead with this.
> >
> > Richard.
> >
> > * tree-vect-slp.cc (vect_build_slp_tree_1): Reject
> > single-lane vector types.
> > ---
> > gcc/tree-vect-slp.cc | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
> > index ad75386926a..d2ce4ffaa4f 100644
> > --- a/gcc/tree-vect-slp.cc
> > +++ b/gcc/tree-vect-slp.cc
> > @@ -1114,6 +1114,15 @@ vect_build_slp_tree_1 (vec_info *vinfo, unsigned char
> > *swap,
> > matches[0] = false;
> > return false;
> > }
> > + if (known_le (TYPE_VECTOR_SUBPARTS (vectype), 1U))
> > + {
> > + if (dump_enabled_p ())
> > + dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
> > + "Build SLP failed: not using single lane "
> > + "vector type %T\n", vectype);
> > + matches[0] = false;
> > + return false;
> > + }
> > /* Record nunits required but continue analysis, producing matches[]
> > as if nunits was not an issue. This allows splitting of groups
> > to happen. */
> > --
> > 2.43.0
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
