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From: "goldstein.w.n at gmail dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug string/29611] Optimized AVX2 string functions unconditionally
 use BMI2 instructions
Date: Mon, 26 Sep 2022 14:05:42 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29611

--- Comment #6 from Noah Goldstein <goldstein.w.n at gmail dot com> ---
(In reply to Aurelien Jarno from comment #5)
> (In reply to Noah Goldstein from comment #3)
> > (In reply to Noah Goldstein from comment #2)
> > > This was fixed by:
> > >=20
> > > commit 83c5b368226c34a2f0a5287df40fc290b2b34359
> > > Author: H.J. Lu <hjl.tools@gmail.com>
> > > Date:   Mon Apr 19 10:45:07 2021 -0700
> > >=20
> > >     x86-64: Require BMI2 for strchr-avx2.S
> > >=20
> > > Which we can probably backport easily. The issue is that some avx2 ch=
anges
> > > where backported without the surrounding ifunc code.
> > >
> >=20
> > I think this needs to be backported to:
> > 2.28-2.32=20
> >=20
> > I applies cleanly on 2.32
> >=20
> > but for 2.28 - 2.31 it depends on:
> >=20
> > commit 107e6a3c2212ba7a3a4ec7cae8d82d73f7c95d0b (HEAD)
> > Author: H.J. Lu <hjl.tools@gmail.com>
> > Date:   Mon Jun 29 16:36:08 2020 -0700
> >=20
> >     x86: Support usable check for all CPU features
> >=20
>=20
> If that one is too complicated to backport to 2.31, maybe it's easier to
> revert the optimization in 2.31?

Would like to get H.Js opinion on that, but maybe.

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