diff options
authorArjan van de Ven <arjan@infradead.org>2009-09-28 12:21:22 (GMT)
committerH. Peter Anvin <hpa@zytor.com>2009-09-28 23:43:15 (GMT)
commitff60fab71bb3b4fdbf8caf57ff3739ffd0887396 (patch)
parent9f0cf4adb6aa0bfccf675c938124e68f7f06349d (diff)
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 Due to some not-so-good behavior in the gcc 3.x series, this change is only done for GCC 4.x and above. Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> LKML-Reference: <20090928142122.6fc57e9c@infradead.org> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
1 files changed, 9 insertions, 0 deletions
diff --git a/arch/x86/include/asm/string_32.h b/arch/x86/include/asm/string_32.h
index ae907e6..3d3e835 100644
--- a/arch/x86/include/asm/string_32.h
+++ b/arch/x86/include/asm/string_32.h
@@ -177,10 +177,15 @@ static inline void *__memcpy3d(void *to, const void *from, size_t len)
+#if (__GNUC__ >= 4)
+#define memcpy(t, f, n) __builtin_memcpy(t, f, n)
#define memcpy(t, f, n) \
(__builtin_constant_p((n)) \
? __constant_memcpy((t), (f), (n)) \
: __memcpy((t), (f), (n)))
* kmemcheck becomes very happy if we use the REP instructions unconditionally,
@@ -316,11 +321,15 @@ void *__constant_c_and_count_memset(void *s, unsigned long pattern,
: __memset_generic((s), (c), (count)))
+#if (__GNUC__ >= 4)
+#define memset(s, c, count) __builtin_memset(s, c, count)
#define memset(s, c, count) \
(__builtin_constant_p(c) \
? __constant_c_x_memset((s), (0x01010101UL * (unsigned char)(c)), \
(count)) \
: __memset((s), (c), (count)))
* find the first occurrence of byte 'c', or 1 past the area if none

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