Devirtualization in GCC

Abstract

A major optimization for object oriented languages is converting dynamically bound function calls into (statically bound) direct calls, a process called devirtualization. This saves the dynamic dispatch overhead, and more importantly, enables further inlining of these function calls. For devirtualization we designed an extension of the Rapid Type Analysis (RTA) algorithm, a fast and effective algorithm [1]. The resulting algorithm combines RTA with a simple data-flow analysis. We have an initial version of devirtualization for C++, implemented in GCC. We describe how the implementation makes use of the existent GCC code, and how it deals with the complexities of the C++ language. Finally we discuss the major implementation issues for completing the implementation.