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byteorder: allow arch to opt to use GCC intrinsics for byteswapping

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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>
This commit is contained in:
David Woodhouse 2012-12-03 16:25:40 +00:00
parent 27d7c2a006
commit cf66bb93e0
4 changed files with 45 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

12
include/uapi/linux/swab.h
View file

@ -45,7 +45,9 @@
static inline __attribute_const__ __u16 __fswab16(__u16 val)
{
#ifdef __arch_swab16
#ifdef __HAVE_BUILTIN_BSWAP16__
return __builtin_bswap16(val);
#elif defined (__arch_swab16)
return __arch_swab16(val);
#else
return ___constant_swab16(val);
@ -54,7 +56,9 @@ static inline __attribute_const__ __u16 __fswab16(__u16 val)
static inline __attribute_const__ __u32 __fswab32(__u32 val)
{
#ifdef __arch_swab32
#ifdef __HAVE_BUILTIN_BSWAP32__
return __builtin_bswap32(val);
#elif defined(__arch_swab32)
return __arch_swab32(val);
#else
return ___constant_swab32(val);
@ -63,7 +67,9 @@ static inline __attribute_const__ __u32 __fswab32(__u32 val)
static inline __attribute_const__ __u64 __fswab64(__u64 val)
{
#ifdef __arch_swab64
#ifdef __HAVE_BUILTIN_BSWAP64__
return __builtin_bswap64(val);
#elif defined (__arch_swab64)
return __arch_swab64(val);
#elif defined(__SWAB_64_THRU_32__)
__u32 h = val >> 32;