Equivalence analysis and its application in improving the efficiency of program slicing

Abstract

Existing methods for handling pointer variables during dataflow analyses can make such analyses inefficient in both time and space because the data-flow analyses must store and propagate large sets of data facts that are introduced by dereferences of pointer variables. This article presents equivalence analysis , a general technique to improve the efficiency of data-flow analyses in the presence of pointer variables. The technique identifies equivalence relations among the memory locations accessed by a procedure, and ensures that two equivalent memory locations share the same set of data facts in a procedure and in the procedures that are called by that procedure. Thus, a data-flow analysis needs to compute the data-flow information for only a representative memory location in an equivalence class. The data-flow information for other memory locations in the equivalence class can be derived from that of the representative memory location. The article also shows the extension to an interprocedural slicing algorithm that uses equivalence analysis to improve the efficiency of the algorithm. Our empirical studies suggest that equivalence analysis may effectively improve the efficiency of many data-flow analyses.