diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2025-03-27 10:56:28 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2025-03-28 23:24:16 +0100 |
| commit | e29c5d0e5dc35ed8b8920b573925d8aa2f8bafb0 (patch) | |
| tree | 63aafc5bf3a1a5dbf4571b7c4419e80d126242c0 | |
| parent | 0717b1392dc7e3f350e5a5d25ea794aa92210684 (diff) | |
x86/bitops: Simplify variable_ffz() as variable__ffs(~word)
Find first zero (FFZ) can be implemented by negating the
input and using find first set (FFS).
Before/after code generation comparison on ffz()-using
kernel code shows that code generation has not changed:
# kernel/signal.o:
text data bss dec hex filename
42121 3472 8 45601 b221 signal.o.before
42121 3472 8 45601 b221 signal.o.after
md5:
ce4c31e1bce96af19b62a5f9659842f1 signal.o.before.asm
ce4c31e1bce96af19b62a5f9659842f1 signal.o.after.asm
[ mingo: Added code generation check. ]
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250327095641.131483-1-ubizjak@gmail.com
| -rw-r--r-- | arch/x86/include/asm/bitops.h | 5 |
1 files changed, 1 insertions, 4 deletions
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h index bbaf75ea6703..eebbc8889e70 100644 --- a/arch/x86/include/asm/bitops.h +++ b/arch/x86/include/asm/bitops.h @@ -267,10 +267,7 @@ static __always_inline unsigned long variable__ffs(unsigned long word) static __always_inline unsigned long variable_ffz(unsigned long word) { - asm("tzcnt %1,%0" - : "=r" (word) - : "r" (~word)); - return word; + return variable__ffs(~word); } /** |