diff options
| -rw-r--r-- | include/linux/bitops.h | 18 |
1 files changed, 17 insertions, 1 deletions
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 3c3afbae1533..cf9bf65039f2 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -33,8 +33,24 @@ extern unsigned long __sw_hweight64(__u64 w); #include <asm-generic/bitops/generic-non-atomic.h> +/* + * Many architecture-specific non-atomic bitops contain inline asm code and due + * to that the compiler can't optimize them to compile-time expressions or + * constants. In contrary, generic_*() helpers are defined in pure C and + * compilers optimize them just well. + * Therefore, to make `unsigned long foo = 0; __set_bit(BAR, &foo)` effectively + * equal to `unsigned long foo = BIT(BAR)`, pick the generic C alternative when + * the arguments can be resolved at compile time. That expression itself is a + * constant and doesn't bring any functional changes to the rest of cases. + * The casts to `uintptr_t` are needed to mitigate `-Waddress` warnings when + * passing a bitmap from .bss or .data (-> `!!addr` is always true). + */ #define bitop(op, nr, addr) \ - op(nr, addr) + ((__builtin_constant_p(nr) && \ + __builtin_constant_p((uintptr_t)(addr) != (uintptr_t)NULL) && \ + (uintptr_t)(addr) != (uintptr_t)NULL && \ + __builtin_constant_p(*(const unsigned long *)(addr))) ? \ + const##op(nr, addr) : op(nr, addr)) #define __set_bit(nr, addr) bitop(___set_bit, nr, addr) #define __clear_bit(nr, addr) bitop(___clear_bit, nr, addr) |