x86: Implement change_bit with immediate operand as "lock xorb"

Impact: Minor optimization.

Implement change_bit with immediate bit count as "lock xorb". This is
similar to  "lock orb" and "lock andb"  for set_bit and clear_bit
functions.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 3600103..9fa9dcd 100644 (file)
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -168,7 +168,15 @@ static inline void __change_bit(int nr, volatile unsigned long *addr)
  */
 static inline void change_bit(int nr, volatile unsigned long *addr)
 {
-       asm volatile(LOCK_PREFIX "btc %1,%0" : ADDR : "Ir" (nr));
+       if (IS_IMMEDIATE(nr)) {
+               asm volatile(LOCK_PREFIX "xorb %1,%0"
+                       : CONST_MASK_ADDR(nr, addr)
+                       : "iq" ((u8)CONST_MASK(nr)));
+       } else {
+               asm volatile(LOCK_PREFIX "btc %1,%0"
+                       : BITOP_ADDR(addr)
+                       : "Ir" (nr));
+       }
 }
 
 /**