Commit bb7379bf authored by Alexander Lobakin's avatar Alexander Lobakin Committed by Yury Norov
Browse files

bitops: define const_*() versions of the non-atomics 



Define const_*() variants of the non-atomic bitops to be used when
the input arguments are compile-time constants, so that the compiler
will be always able to resolve those to compile-time constants as
well. Those are mostly direct aliases for generic_*() with one
exception for const_test_bit(): the original one is declared
atomic-safe and thus doesn't discard the `volatile` qualifier, so
in order to let optimize code, define it separately disregarding
the qualifier.
Add them to the compile-time type checks as well just in case.

Suggested-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarAlexander Lobakin <alexandr.lobakin@intel.com>
Reviewed-by: default avatarMarco Elver <elver@google.com>
Reviewed-by: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarYury Norov <yury.norov@gmail.com>
parent 0e862838

include/asm-generic/bitops/generic-non-atomic.h

+31 −0
Original line number Diff line number Diff line
@@ -127,4 +127,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr) 
	return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));

}



/*

 * const_*() definitions provide good compile-time optimizations when

 * the passed arguments can be resolved at compile time.

 */

#define const___set_bit			generic___set_bit

#define const___clear_bit		generic___clear_bit

#define const___change_bit		generic___change_bit

#define const___test_and_set_bit	generic___test_and_set_bit

#define const___test_and_clear_bit	generic___test_and_clear_bit

#define const___test_and_change_bit	generic___test_and_change_bit



/**

 * const_test_bit - Determine whether a bit is set

 * @nr: bit number to test

 * @addr: Address to start counting from

 *

 * A version of generic_test_bit() which discards the `volatile` qualifier to

 * allow a compiler to optimize code harder. Non-atomic and to be called only

 * for testing compile-time constants, e.g. by the corresponding macros, not

 * directly from "regular" code.

 */

static __always_inline bool

const_test_bit(unsigned long nr, const volatile unsigned long *addr)

{

	const unsigned long *p = (const unsigned long *)addr + BIT_WORD(nr);

	unsigned long mask = BIT_MASK(nr);

	unsigned long val = *p;



	return !!(val & mask);

}



#endif /* __ASM_GENERIC_BITOPS_GENERIC_NON_ATOMIC_H */

include/linux/bitops.h

+1 −0
Original line number Diff line number Diff line
@@ -37,6 +37,7 @@ extern unsigned long __sw_hweight64(__u64 w); 
/* Check that the bitops prototypes are sane */

#define __check_bitop_pr(name)						\

	static_assert(__same_type(arch_##name, generic_##name) &&	\

		      __same_type(const_##name, generic_##name) &&	\

		      __same_type(name, generic_##name))



__check_bitop_pr(__set_bit);