Class hierarchy specialization

Abstract.

Many class libraries are designed with an emphasis on generality and extensibility. Applications often exercise only part of a library's functionality. As a result, the objects created by an application may contain unused (user-specified or compiler-generated) members. Redundant members in objects are undesirable because they increase an application's memory usage.

We present an algorithm for specializing a class hierarchy with respect to its usage in a program $\cal P$. That is, the algorithm analyzes the member access patterns for $\cal P$'s variables, and creates distinct classes for variables that access different members. The algorithm addresses the inheritance mechanisms of C++ in their full generality, including multiple inheritance and virtual (shared) inheritance.

Class hierarchy specialization reduces object size, and can be viewed as a space optimization. However, execution time may also be reduced through reduced object creation or destruction time, and caching and paging effects. Class hierarchy specialization may also create new opportunities for existing optimizations such as call devirtualization and inlining. In addition, specialization may be useful in tools for software maintenance and program understanding.