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Message-Id: <200909291444.06422.arnd@arndb.de>
Date: Tue, 29 Sep 2009 14:44:06 +0200
From: Arnd Bergmann <arnd@...db.de>
To: Arjan van de Ven <arjan@...radead.org>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...x.de,
hpa@...or.com, torvalds@...ux-foundation.org
Subject: Re: [PATCH] x86: Use __builtin_memset and __builtin_memcpy for memset/memcpy
On Monday 28 September 2009, Arjan van de Ven wrote:
>
> GCC provides reasonable memset/memcpy functions itself, with __builtin_memset
> and __builtin_memcpy. For the "unknown" cases, it'll fall back to our
> current existing functions, but for fixed size versions it'll inline
> something smart. Quite often that will be the same as we have now,
> but sometimes it can do something smarter (for example, if the code
> then sets the first member of a struct, it can do a shorter memset).
>
> In addition, and this is more important, gcc knows which registers and
> such are not clobbered (while for our asm version it pretty much
> acts like a compiler barrier), so for various cases it can avoid reloading
> values.
>
> The effect on codesize is shown below on my typical laptop .config:
>
> text data bss dec hex filename
> 5605675 2041100 6525148 14171923 d83f13 vmlinux.before
> 5595849 2041668 6525148 14162665 d81ae9 vmlinux.after
>
The patch looks good, but is there a reason to keep it architecture
specific? I would guess that the same logic applies to all architectures
with gcc-4.x and could be put into include/linux/compiler-gcc4.h.
Arnd <><
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