From: Nicolas Pitre Date: Tue, 10 Jan 2006 19:48:02 +0000 (+0000) Subject: [ARM] 3252/1: help gcc do the best with ___arch__swab32 X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=a3e49436867e6c7acc1b5eed21d30c88d156825b;p=openwrt%2Fstaging%2Fblogic.git [ARM] 3252/1: help gcc do the best with ___arch__swab32 Patch from Nicolas Pitre Depending on your gcc version, the current C-only implementation would produce suboptimal code, ranging from a bad register selection forcing an additional mov instruction to a failure to merge the eor and the ror in a single instruction. With a little help gcc always produces the best code. Signed-off-by: Nicolas Pitre Signed-off-by: Russell King --- diff --git a/include/asm-arm/byteorder.h b/include/asm-arm/byteorder.h index 741f5bc5d016..17eaf8bdf092 100644 --- a/include/asm-arm/byteorder.h +++ b/include/asm-arm/byteorder.h @@ -22,7 +22,16 @@ static inline __attribute_const__ __u32 ___arch__swab32(__u32 x) { __u32 t; - t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */ + if (__builtin_constant_p(x)) { + t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */ + } else { + /* + * The compiler needs a bit of a hint here to always do the + * right thing and not screw it up to different degrees + * depending on the gcc version. + */ + asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x)); + } x = (x << 24) | (x >> 8); /* mov r0,r0,ror #8 */ t &= ~0x00FF0000; /* bic r1,r1,#0x00FF0000 */ x ^= (t >> 8); /* eor r0,r0,r1,lsr #8 */