[GIT *] Preparatory patch for using GCC intrinsics for byteswapping

[GIT *] Preparatory patch for using GCC intrinsics for byteswapping

[David Woodhouse]

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Linus, please pull from
	git://git.infradead.org/users/dwmw2/byteswap.git byteswap-for-linus-20121219

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.

David Woodhouse (1):
      byteorder: allow arch to opt to use GCC intrinsics for byteswapping

 arch/Kconfig                   | 19 +++++++++++++++++++
 include/linux/compiler-gcc4.h  | 10 ++++++++++
 include/linux/compiler-intel.h |  7 +++++++
 include/uapi/linux/swab.h      | 12 +++++++++---
 4 files changed, 45 insertions(+), 3 deletions(-)

-- 
David Woodhouse                            Open Source Technology Centre
David.Woodhouse@intel.com                              Intel Corporation




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