Methods, systems, computer-readable media, and apparatus for determining function side effects of a program function are disclosed. Source code of one or more prototype functions that is configured to simulate the function side-effect behaviors of a program function can be provided, and the compiler can determine the functional side effects of the program function in various specific program contexts based on the source code of the prototype functions rather than the source code of the program function. Optimization procedures can be performed based on the function side effects of the program function derived from the prototype functions and the program contexts.