Messages in this thread |  | | | Subject | Re: [PATCH] x86: Use __builtin_memset and __builtin_memcpy for memset/memcpy | | From | Andi Kleen <> | | Date | Fri, 02 Oct 2009 21:19:18 +0200 |
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Arjan van de Ven <arjan@infradead.org> writes:
> From ebb81aab0c3df19771ebc0eec1261ae314ddc0af Mon Sep 17 00:00:00 2001 > From: Arjan van de Ven <arjan@linux.intel.com> > Date: Mon, 28 Sep 2009 11:21:32 +0200 > Subject: [PATCH] x86: Use __builtin_memset and __builtin_memcpy for memset/memcpy > > 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
I tried this some time ago, but it it generates bad code on some gcc 3 versions.
You really need to test such kind of changes on a wide variety of compilers, not assuming everyone uses the same version as you.
-Andi
-- ak@linux.intel.com -- Speaking for myself only.
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