If the address of the swapped memory location is known at compile time,
we can check its alignment at no runtime cost and use lswapl instead.
text data bss dec hex filename
before: 1872820 52136 78040 2002996 1e9034 hw/xfree86/Xorg
after: 1864396 52136 78040 1994572 1e6f4c hw/xfree86/Xorg
bswap instructions: 131 -> 308 (used in lswapl)
rol instructions: 943 -> 1174 (used in lswaps)
Signed-off-by: Matt Turner <[email protected]>
---
include/misc.h | 15 +++++++++++++--
1 files changed, 13 insertions(+), 2 deletions(-)
diff --git a/include/misc.h b/include/misc.h
index cfe734f..b340591 100644
--- a/include/misc.h
+++ b/include/misc.h
@@ -270,6 +270,11 @@ void __attribute__((error("wrong sized variable passed to
swap"))) wrong_size(vo
static inline void wrong_size(void)
{
}
+
+static inline void __builtin_constant_p(int x)
+{
+ return 0;
+}
#endif
/* byte swap a 32-bit value */
@@ -286,7 +291,10 @@ static inline void swap_uint32(uint32_t *x)
#define swapl(x) do { \
if (sizeof(*(x)) != 4) \
wrong_size(); \
- swap_uint32((uint32_t *)(x)); \
+ if (__builtin_constant_p((uintptr_t)(x) & 3) && ((uintptr_t)(x)
& 3) == 0) \
+ *(x) = lswapl(*(x)); \
+ else \
+ swap_uint32((uint32_t *)(x)); \
} while (0)
/* byte swap a 16-bit value */
@@ -300,7 +308,10 @@ static inline void swap_uint16(uint16_t *x)
#define swaps(x) do { \
if (sizeof(*(x)) != 2) \
wrong_size(); \
- swap_uint16((uint16_t *)(x)); \
+ if (__builtin_constant_p((uintptr_t)(x) & 1) && ((uintptr_t)(x)
& 1) == 0) \
+ *(x) = lswaps(*(x)); \
+ else \
+ swap_uint16((uint16_t *)(x)); \
} while (0)
/* copy 32-bit value from src to dst byteswapping on the way */
--
1.7.3.4
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