Using profile-directed feedback (PDF)

In any large application, there are sections of code that are not often executed, such as code for error-handling. A traditional compiler cannot tell what these low frequency sections of code or functions are, and may spend a lot of time optimizing code that will never be executed. PDF can be used to collect information about the way the program is really used and the compiler can use this information when optimizing the code. PDF also enables you to receive estimates on how many times loops are iterated.