likely/unlikely macro.

[<shinny@j02.itscom.net>]

Hi,

How may I ask for your help?
Now I'm studying the linux scheduler(sched.c).
And I'm wondering what likey()/unlikely macros mean.
I could find they're defined in linux/compiler.h as follows.

/*
 * Generic compiler-dependent macros required for kernel
 * build go below this comment. Actual compiler/compiler version
 * specific implementations come from the above header files
 */

#define likely(x)	__builtin_expect(!!(x), 1)
#define unlikely(x)	__builtin_expect(!!(x), 0)

And I could find __builtin_expect()'s definition only in linux/compiler-gcc2.h as a follow.
I don't know what's going if __GNUC_MINOR__ is over 96, though...

#if __GNUC_MINOR__ < 96
# define __builtin_expect(x, expected_value) (x)
#endif

As a result, although it seems likely() and unlikely() do nothing, is my expectation correct?
If there are other references about this, please let me know.

Regards,
Shinpei Kato
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