MIPS: Use ARCH_USE_BUILTIN_BSWAP.

ARCH_USE_BUILTIN_BSWAP will use __builtin_bswap16(), __builtin_bswap32()
and __builtin_bswap64() where available.  This allows better instruction
scheduling.  On pre-R2 processors it will result in 32 bit and 64 bit
swapping being performed in a call to a __bswapsi2() rsp. __bswapdi2()
functions, so we add these, too.

For a 4.2 kernel with GCC 4.9 this yields the following kernel sizes:

   text    data     bss     dec     hex filename
3996071  155804   88992 4240867  40b5e3 vmlinux         ip22 baseline
3985687  159900   88992 4234579  409d53 vmlinux         ip22 + bswap patch
6913157  378552  251024 7542733  7317cd vmlinux         ip27 baseline
6878581  378552  251024 7508157  7290bd vmlinux         ip27 + bswap patch
5773777  268752  187424 6229953  5f0fc1 vmlinux         malta baseline
5773401  268752  187424 6229577  5f0e49 vmlinux         malta + bswap patch

Presumably the code size improvments yield better cache hit rate thus
better performance compensating for the extra function call but this
will still need to be benchmarked.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/mips/lib/bswapsi.c b/arch/mips/lib/bswapsi.c
new file mode 100644
index 000000000000..2b302ff121d2
--- /dev/null
+++ b/arch/mips/lib/bswapsi.c
@@ -0,0 +1,11 @@
+#include <linux/module.h>
+
+unsigned int __bswapsi2(unsigned int u)
+{
+	return (((u) & 0xff000000) >> 24) |
+	       (((u) & 0x00ff0000) >>  8) |
+	       (((u) & 0x0000ff00) <<  8) |
+	       (((u) & 0x000000ff) << 24);
+}
+
+EXPORT_SYMBOL(__bswapsi2);