Messages in this thread Patch in this message | | | Date | Mon, 28 Sep 2009 11:34:33 +0200 | From | Arjan van de Ven <> | Subject | [PATCH] x86: Use __builtin_memset and __builtin_memcpy for memset/memcpy |
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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
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> --- arch/x86/include/asm/string_32.h | 11 ++--------- 1 files changed, 2 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h index ae907e6..23a0bc2 100644 --- a/arch/x86/include/asm/string_32.h +++ b/arch/x86/include/asm/string_32.h @@ -177,10 +177,7 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len) */ #ifndef CONFIG_KMEMCHECK -#define memcpy(t, f, n) \ - (__builtin_constant_p((n)) \ - ? __constant_memcpy((t), (f), (n)) \ - : __memcpy((t), (f), (n))) +#define memcpy(t, f, n) __builtin_memcpy(t, f, n) #else /* * kmemcheck becomes very happy if we use the REP instructions unconditionally, @@ -316,11 +313,7 @@ void *__constant_c_and_count_memset(void *s, unsigned long pattern, : __memset_generic((s), (c), (count))) #define __HAVE_ARCH_MEMSET -#define memset(s, c, count) \ - (__builtin_constant_p(c) \ - ? __constant_c_x_memset((s), (0x01010101UL * (unsigned char)(c)), \ - (count)) \ - : __memset((s), (c), (count))) +#define memset(s, c, count) __builtin_memset(s, c, count) /* * find the first occurrence of byte 'c', or 1 past the area if none -- 1.6.2.5
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
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