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From: "rguenther at suse dot de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/109499] Unnecessary zeroing in SVE loops
Date: Thu, 13 Apr 2023 13:21:49 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109499

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 13 Apr 2023, rsandifo at gcc dot gnu.org wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109499
>=20
> --- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.=
org> ---
> (In reply to Richard Biener from comment #1)
> > Is there not enough info to catch this on the RTL level with a peephole?
> That works for simple cases like the first loop.  But in general, I think=
 we
> want the full power of gimple to push the information down.  The second l=
oop is
> one example of that, but in general, there could be a chain of operations=
 that
> naturally do the right thing for inactive lanes.

AVX512 masking allows merge and zero modes, zero being cheaper=20
(obviously).  I think "zero" is what all targets support so we could
define GIMPLE to be that way - inactive lanes become zero.  That's
then also less of a "partial definition" and "undefined" should be
avoided at best?=