Transformation to Dynamic Single Assignment Using a Simple Data Flow Analysis

This paper presents a novel method to construct a dynamic single assignment (DSA) form of array-intensive, pointer-free C programs (or in any other procedural language). A program in DSA form does not perform any destructive update of scalars and array elements, i.e., each element is written at most once. As DSA makes the dependencies between variable references explicit, it facilitates complex analyses and optimizations of programs. Existing transformations into DSA perform a complex data flow analysis with exponential analysis time and work only for a limited set of input programs. Our method removes irregularities from the data flow by adding copy assignments to the program, and then it can use simple data flow analyses. The DSA transformation presented scales very well with growing program sizes and overcomes a number of important limitations of existing methods. We have implemented the method and it is being used in the context of memory optimization and verification of those optimizations.