Eliminating virtual function calls in C++ programs

Abstract

We have designed and implemented an optimizing source-to-source C++ compiler that reduces the frequency of virtual function calls. Our prototype implementation demonstrates the value of OO-specific optimization for C++. Despite some limitations of our system, and despite the low frequency of virtual function calls in some of the programs, optimization improves the performance of a suite of large C++ applications totalling over 90,000 lines of code by a median of 18% over the original programs and reduces the number of virtual function calls by a median factor of five. For more call-intensive versions of the same programs, performance improved by a median of 26% and the number of virtual calls dropped by a factor of 17.5. Our measurements indicate thatinlining barely increases code size, and that for most programs, the instruction cache miss ratio does not increase significantly.