likely/unlikely equivalent for MSVC

Question

GCC compiler supports __builtin_expect statement that is used to define likely and unlikely macros.

eg.

#define likely(expr)    (__builtin_expect(!!(         


        

Answer 1

According to Branch and Loop Reorganization to Prevent Mispredicts document from Intel:

In order to effectively write your code to take advantage of these rules, when writing if-else or switch statements, check the most common cases first and work progressively down to the least common.

Unfortunately you cannot write something like

#define if_unlikely(cond) if (!(cond)); else 

because MSVC optimizer as of VS10 ignores such "hint".

As I prefer to deal with errors first in my code, I seem to write less efficient code. Fortunately, second time CPU encounters the branch it will use its statistics instead of a static hint.