diff options
| author | David Woodhouse <David.Woodhouse@intel.com> | 2012-12-03 16:25:40 +0000 |
|---|---|---|
| committer | David Woodhouse <David.Woodhouse@intel.com> | 2012-12-06 01:22:31 +0000 |
| commit | cf66bb93e0f75e0a4ba1ec070692618fa028e994 (patch) | |
| tree | 0ae48658adb29f50bdd85a94cbb84670a234f441 /include/linux/compiler-gcc4.h | |
| parent | 27d7c2a006a81c04fab00b8cd81b99af3b32738d (diff) | |
byteorder: allow arch to opt to use GCC intrinsics for byteswapping
Since GCC 4.4, there have been __builtin_bswap32() and __builtin_bswap16()
intrinsics. A __builtin_bswap16() came a little later (4.6 for PowerPC,
48 for other platforms).
By using these instead of the inline assembler that most architectures
have in their __arch_swabXX() macros, we let the compiler see what's
actually happening. The resulting code should be at least as good, and
much *better* in the cases where it can be combined with a nearby load
or store, using a load-and-byteswap or store-and-byteswap instruction
(e.g. lwbrx/stwbrx on PowerPC, movbe on Atom).
When GCC is sufficiently recent *and* the architecture opts in to using
the intrinsics by setting CONFIG_ARCH_USE_BUILTIN_BSWAP, they will be
used in preference to the __arch_swabXX() macros. An architecture which
does not set ARCH_USE_BUILTIN_BSWAP will continue to use its own
hand-crafted macros.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Acked-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'include/linux/compiler-gcc4.h')
| -rw-r--r-- | include/linux/compiler-gcc4.h | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/include/linux/compiler-gcc4.h b/include/linux/compiler-gcc4.h index 412bc6c2b023..dc16a858e77c 100644 --- a/include/linux/compiler-gcc4.h +++ b/include/linux/compiler-gcc4.h @@ -63,3 +63,13 @@ #define __compiletime_warning(message) __attribute__((warning(message))) #define __compiletime_error(message) __attribute__((error(message))) #endif + +#ifdef CONFIG_ARCH_USE_BUILTIN_BSWAP +#if __GNUC_MINOR__ >= 4 +#define __HAVE_BUILTIN_BSWAP32__ +#define __HAVE_BUILTIN_BSWAP64__ +#endif +#if __GNUC_MINOR__ >= 8 || (defined(__powerpc__) && __GNUC_MINOR__ >= 6) +#define __HAVE_BUILTIN_BSWAP16__ +#endif +#endif |