[tip: x86/asm] x86/bitops: Use TZCNT mnemonic in <asm/bitops.h>

[tip-bot2 for Uros Bizjak]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     0717b1392dc7e3f350e5a5d25ea794aa92210684
Gitweb:        https://git.kernel.org/tip/0717b1392dc7e3f350e5a5d25ea794aa92210684
Author:        Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate:    Tue, 25 Mar 2025 18:52:01 +01:00
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Tue, 25 Mar 2025 22:38:29 +01:00

x86/bitops: Use TZCNT mnemonic in <asm/bitops.h>

Current minimum required version of binutils is 2.25,
which supports TZCNT instruction mnemonic.

Replace "REP; BSF" in variable__{ffs,ffz}() function
with this proper mnemonic.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20250325175215.330659-1-ubizjak@xxxxxxxxx
---
 arch/x86/include/asm/bitops.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 100413a..bbaf75e 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -248,7 +248,7 @@ arch_test_bit_acquire(unsigned long nr, const volatile unsigned long *addr)
 
 static __always_inline unsigned long variable__ffs(unsigned long word)
 {
-	asm("rep; bsf %1,%0"
+	asm("tzcnt %1,%0"
 		: "=r" (word)
 		: ASM_INPUT_RM (word));
 	return word;
@@ -267,7 +267,7 @@ static __always_inline unsigned long variable__ffs(unsigned long word)
 
 static __always_inline unsigned long variable_ffz(unsigned long word)
 {
-	asm("rep; bsf %1,%0"
+	asm("tzcnt %1,%0"
 		: "=r" (word)
 		: "r" (~word));
 	return word;