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From: "Bonzini" <bonzini@gnu.org>
To: <kevin@atkinson.dhs.org>
Cc: <gcc@gcc.gnu.org>
Subject: Re: Slow memcmp for aligned strings on Pentium 3
Date: Fri, 04 Apr 2003 14:33:00 -0000	[thread overview]
Message-ID: <003301c2fa70$5beff990$6edc1d97@bonz> (raw)

> I was doing some tests with with memcmp and it seams that gcc 3.2.2
> always uses cmps, even for aligned strings.

I also had a very fast memcmp that also worked word-by-word in the unaligned case
(using some bit-twiddling tricks with SHRD), but I never had the time to polish it for
inclusion in glibc.  It turned out however that CMPS is as fast as mine (or even
faster) on AMD chips.

I do think anyway that memcmp expansion in gcc should be disabled unless optimizing for
size or unless the size is known to be small, say 16 bytes.

See these posts:

http://gcc.gnu.org/ml/gcc/2002-10/msg01616.html (me)
http://gcc.gnu.org/ml/gcc/2002-10/msg01637.html (Roger)
http://sources.redhat.com/ml/libc-alpha/2002-10/msg00511.html (source)

Paolo

             reply	other threads:[~2003-04-04  9:35 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-04-04 14:33 Bonzini [this message]
  -- strict thread matches above, loose matches on Subject: below --
2003-04-04 17:13 Jerry Quinn
2003-04-04 17:29 ` Kevin Atkinson
2003-04-06  5:54   ` Jerry Quinn
2003-04-06 22:17     ` Kevin Atkinson
2003-04-07 17:30       ` Jerry Quinn
2003-04-04 13:18 Roger Sayle
2003-04-04 14:51 ` Kevin Atkinson
2003-04-04 17:08 ` Kevin Atkinson
2003-04-04 18:58   ` Marcel Cox
2003-04-04 19:27     ` Kevin Atkinson
2003-04-04  6:22 Kevin Atkinson
2003-04-04  8:52 ` Zack Weinberg
2003-04-04 15:16   ` Kevin Atkinson

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