unlikely
#define unlikely(expr) expect((expr) != 0, 0)
#define unlikely(expr) expect((expr) != 0, 0)
#define unlikely(x) _zfs_expect((x) != 0, 0)
#define unlikely(x) _zfs_expect((x) != 0, 0)
#define unlikely(a) (a)
#define unlikely(x) __builtin_expect((x), 0)
#define unlikely(x) (x)
#define unlikely(expr) (expr)