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 <xnmtof4ss3.fsf@greed.delorie.com>
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From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Tue, 14 Sep 2021 00:55:07 -0500
Message-ID: <CAFUsyfL+F-SqYo=PXjCimLUgf_U62=f_8uVY-=qh=BruNwMMNQ@mail.gmail.com>
Subject: Re: [PATCH 5/5] x86_64: Add evex optimized bcmp implementation in
 bcmp-evex.S
To: DJ Delorie <dj@redhat.com>
Cc: "Carlos O'Donell" <carlos@redhat.com>,
 GNU C Library <libc-alpha@sourceware.org>
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On Tue, Sep 14, 2021 at 12:42 AM DJ Delorie <dj@redhat.com> wrote:

> Noah Goldstein <goldstein.w.n@gmail.com> writes:
> > I'm not 100% sure what you mean? memcmp can correctly implement bcmp
> > but not the vice versa.
>
> glibc does not have a separate implementation of bcmp().  Any calls to
> bcmp() end up calling memcmp() (through that weak alias).  So your patch
> is not *optimizing* bcmp, it is *adding* bcmp.  The new version you are
> adding is no longer using the optimized versions of memcmp, so you'd
> have to either (1) be very careful to not introduce a performance
> regression, or (2) optimize the existing memcmp()s further instead.
>

Ah, got it.

In the first patch of the set:
[PATCH 1/5] x86_64: Add support for bcmp using sse2, sse4_1, avx2, and evex

I have some performance numbers. Seems to be an improvement for avx2/evex.
The sse2/sse4 stuff is a bit more iffy. I don't really have the hardware to
properly
test those versions.

Thank you for all the help!