Following a relatively recent compiler change, make use of the fact that for non-zero input BSF and TZCNT produce the same result, and that CPUs not knowing of TZCNT will treat the instruction as BSF (i.e. ignore what looks like a REP prefix to them). The assumption here is that TZCNT would never have worse performance than BSF.
Signed-off-by: Jan Beulich <jbeul...@suse.com> Cc: Linus Torvalds <torva...@linux-foundation.org> --- v2: Do this unconditionally, and change title accordingly. --- arch/x86/include/asm/bitops.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- 3.6-rc6/arch/x86/include/asm/bitops.h +++ 3.6-rc6-x86-bsf-tzcnt/arch/x86/include/asm/bitops.h @@ -355,7 +355,7 @@ static int test_bit(int nr, const volati */ static inline unsigned long __ffs(unsigned long word) { - asm("bsf %1,%0" + asm("rep; bsf %1,%0" : "=r" (word) : "rm" (word)); return word; @@ -369,7 +369,7 @@ static inline unsigned long __ffs(unsign */ static inline unsigned long ffz(unsigned long word) { - asm("bsf %1,%0" + asm("rep; bsf %1,%0" : "=r" (word) : "r" (~word)); return word; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/