compiler.h: add support for function attribute assume_aligned

#define __visible	__attribute__((externally_visible))

#endif

#if GCC_VERSION >= 40900

/*

 * __assume_aligned(n, k): Tell the optimizer that the returned

 * pointer can be assumed to be k modulo n. The second argument is

 * optional (default 0), so we use a variadic macro to make the

 * shorthand.

 *

 * Beware: Do not apply this to functions which may return

 * ERR_PTRs. Also, it is probably unwise to apply it to functions

 * returning extra information in the low bits (but in that case the

 * compiler should see some alignment anyway, when the return value is

 * massaged by 'flags = ptr & 3; ptr &= ~3;').

 */

#define __assume_aligned(a, ...) __attribute__((__assume_aligned__(a, ## __VA_ARGS__)))

#endif

/*

 * GCC 'asm goto' miscompiles certain code sequences:

 *

#define __visible

#endif

/*

 * Assume alignment of return value.

 */

#ifndef __assume_aligned

#define __assume_aligned(a, ...)

#endif

/* Are two types/vars the same type (ignoring qualifiers)? */

#ifndef __same_type

# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))