linux-kernel - Re: kernel + gcc 4.1 = several problems

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Message-Id: <11fc5e81b224467e25caaefb66ba82e7@kernel.crashing.org>
Date:	Sun, 7 Jan 2007 16:10:53 +0100
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Denis Vlasenko <vda.linux@...glemail.com>
Cc:	akpm@...l.org, Albert Cahalan <acahalan@...il.com>,
	linux-kernel@...r.kernel.org, s0348365@....ed.ac.uk,
	Linus Torvalds <torvalds@...l.org>, bunk@...sta.de,
	mikpe@...uu.se
Subject: Re: kernel + gcc 4.1 = several problems

> I want this:
>
> char v[4];
> ...
> 	memcmp(v, "abcd", 4) == 0
>
> compile to single cmpl on i386. This (gcc 4.1.1) is ridiculous:

>         call    memcmp

i686-linux-gcc (GCC) 4.2.0 20060410 (experimental)

         movl    $4, %ecx        #, tmp65
         cld
         movl    $v, %esi        #, tmp63
         movl    $.LC0, %edi     #, tmp64
         repz
         cmpsb
         sete    %al     #, tmp68

Still not perfect, but better already.  If you have any
specific examples that you'd like to have compiled to
better code, please report them in GCC bugzilla (with a
self-contained testcase, please).


Segher

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