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From: "hjl.tools at gmail dot com" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug string/27457] vzeroupper use in AVX2 multiarch string functions
 cause HTM aborts
Date: Mon, 01 Mar 2021 13:27:08 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27457

--- Comment #12 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Florian Weimer from comment #9)
> (In reply to rguenther from comment #7)
> > On Mon, 1 Mar 2021, fweimer at redhat dot com wrote:
> > > The sources do not seem to show the selection logic.
> > > __memset_avx2_unaligned_rtm seems to simply have dropped the VZEROUPP=
ER
> > > instruction, which can't be good for general application performance.
> >=20
> > The intent was to use %ymm16+ only which does not cause any transition
> > penalty even w/o vzeroupper.
>=20
> I still saw %ymm0 usage in the disassembly, if I recall correctly. And for
> AVX2, there isn't much choice. I didn't try to reverse-engineer the
> corresponding IFUNC selector.
>=20

memset-evex-unaligned-erms.S has

# define VEC_SIZE       32
# define XMM0           xmm16
# define YMM0           ymm16
# define VEC0           ymm16
# define VEC(i)         VEC##i
# define VMOVU          vmovdqu64
# define VMOVA          vmovdqa64
# define VZEROUPPER

There are no %ymm0 nor vzeroupper.

--=20
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