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From: "tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/113441] [14 Regression] Fail to fold the last
 element with multiple loop since g:2efe3a7de0107618397264017fb045f237764cc7
Date: Tue, 27 Feb 2024 08:01:57 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113441

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

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

--- Comment #29 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to rguenther@suse.de from comment #28)
> On Mon, 26 Feb 2024, tnfchris at gcc dot gnu.org wrote:
>=20
> > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113441
> >=20
> > --- Comment #27 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
> > Created attachment 57538 [details]
> >   --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=3D57538&action=3De=
dit
> > proposed1.patch
> >=20
> > proposed patch, this gets the gathers and scatters back. doing regressi=
on run.
>=20
> I don't think this will fly.

Well.. I don't really know what the do here I guess.

per the discussion on irc, we only used to try gather/scatters when SCEV fa=
ils.

Now that it succeeds we no longer try using the pattern and try to handle it
during vectorizable_load/vectorizable_stores as recognizing the gather/scat=
ters
inline through VMAT_GATHER_SCATTER.

This works fine for normal gather and scatters but doesn't work for widening
gathers and narrowing scatters which only the pattern seems to handle.

I don't know how to get this to be detected through get_load_store_type sin=
ce
well, that's very late.  among others we've already determined the VF and t=
he
unpacks have already been marked relevant. So
vectorizable_load/vectorizable_store would have to actively change the IL.

So I don't know how widening and narrowing operations are supposed to work
here.  given that.. I will leave it up to the maintainers I guess.=