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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: Wed, 28 Sep 2022 15:52:59 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D29611

--- Comment #12 from Noah Goldstein <goldstein.w.n at gmail dot com> ---
(In reply to Aurelien Jarno from comment #11)
> Before trying to fix that in older branches, we should start by fixing
> master. 3 groups of functions are using BMI2: memchr, strchr and strlen.
> * strchr is fixed by this commit:
>=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
> * strlen is fixed by this commit:
>=20
> commit aaa23c35071537e2dcf5807e956802ed215210aa
> Author: Noah Goldstein <goldstein.w.n@gmail.com>
> Date:   Mon Apr 19 19:36:07 2021 -0400
>=20
>     x86: Optimize strlen-avx2.S
>=20
> * memchr is not yet fixed in master
memchr should be fine in master.

It uses ifunc-evex.h which has a BMI2 check for avx2:
https://sourceware.org/git/?p=3Dglibc.git;a=3Dblob;f=3Dsysdeps/x86_64/multi=
arch/ifunc-evex.h;h=3D310cfd269f5e4a4a94e96ab971201ae55a41b0b8;hb=3DHEAD#l37
>=20
> So the first step is to fix memchr.

--=20
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