in include/asm/bitops.h [45:56]
static inline void FNAME(int nr, volatile unsigned long *addr) \
{ \
unsigned char *b_addr; \
unsigned char bit = nr & 7; \
\
b_addr = (unsigned char *)addr + ((nr >> 3) ^ 3); \
if (__builtin_constant_p(nr)) { \
__asm__(OP " %1,%0" : "+WU"(*b_addr) : "i"(nr & 7)); \
} else { \
__asm__(OP " %s1,%0" : "+WU"(*b_addr) : "r"(bit)); \
} \
}