__builtin_expect
You can use the __builtin_expect built-in function to indicate that an expression is likely to evaluate to a specified value. The compiler can use this knowledge to direct optimizations. This built-in function is portable with the GNU C/C++ __builtin_expect function.
The prototype of this built-in function is as
follows:
long __builtin_expect (long exp, long c);If exp does not actually evaluate at run time to the predicted value c, performance might suffer. Therefore, you must use this built-in function with caution.
