1. A computer-implemented method of finding portions of a computer program exhibiting irregular performance, the method comprising: detecting an entry into a function of a computer program under test indicating a current execution of the function; responsive to detecting an exit from the function, determining a count of a computing resource utilized by the function during the current execution of the function; comparing the count of the computing resource with a count range determined according to at least one prior execution of the function; and selectively representing the function within a call graph as a plurality of nodes according to the comparing the count of the computing resource with a count range determined according to at least one prior execution of the function.