Merge tag 'byteswap-for-linus-20121219' of git://git.infradead.org/users/dwmw2/byteswap

Pull preparatory gcc intrisics bswap patch from David Woodhouse:
 "This single patch is effectively a no-op for now.  It enables
  architectures to opt in to using GCC's __builtin_bswapXX() intrinsics
  for byteswapping, and if we merge this now then the architecture
  maintainers can enable it for their arch during the next cycle without
  dependency issues.

  It's worth making it a par-arch opt-in, because although in *theory*
  the compiler should never do worse than hand-coded assembler (and of
  course it also ought to do a lot better on platforms like Atom and
  PowerPC which have load-and-swap or store-and-swap instructions), that
  isn't always the case.  See

     http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46453

  for example."

* tag 'byteswap-for-linus-20121219' of git://git.infradead.org/users/dwmw2/byteswap:
  byteorder: allow arch to opt to use GCC intrinsics for byteswapping

4 files changed, 45 insertions, 3 deletions

diff --git a/arch/Kconfig b/arch/Kconfig
index 54ffd0f9df21..8e9e3246b2b4 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -113,6 +113,25 @@ config HAVE_EFFICIENT_UNALIGNED_ACCESS
           See Documentation/unaligned-memory-access.txt for more
           information on the topic of unaligned memory accesses.
 
+config ARCH_USE_BUILTIN_BSWAP
+       bool
+       help
+         Modern versions of GCC (since 4.4) have builtin functions
+         for handling byte-swapping. Using these, instead of the old
+         inline assembler that the architecture code provides in the
+         __arch_bswapXX() macros, allows the compiler to see what's
+         happening and offers more opportunity for optimisation. In
+         particular, the compiler will be able to combine the byteswap
+         with a nearby load or store and use load-and-swap or
+         store-and-swap instructions if the architecture has them. It
+         should almost *never* result in code which is worse than the
+         hand-coded assembler in <asm/swab.h>.  But just in case it
+         does, the use of the builtins is optional.
+
+         Any architecture with load-and-swap or store-and-swap
+         instructions should set this. And it shouldn't hurt to set it
+         on architectures that don't have such instructions.
+
 config HAVE_SYSCALL_WRAPPERS
         bool
 
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
diff --git a/include/linux/compiler-intel.h b/include/linux/compiler-intel.h
index d8e636e5607d..973ce10c40b6 100644
--- a/include/linux/compiler-intel.h
+++ b/include/linux/compiler-intel.h
@@ -29,3 +29,10 @@
 #endif
 
 #define uninitialized_var(x) x
+
+#ifndef __HAVE_BUILTIN_BSWAP16__
+/* icc has this, but it's called _bswap16 */
+#define __HAVE_BUILTIN_BSWAP16__
+#define __builtin_bswap16 _bswap16
+#endif
+
diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
index e811474724c2..0e011eb91b5d 100644
--- a/include/uapi/linux/swab.h
+++ b/include/uapi/linux/swab.h
@@ -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;