A Conservative Data Flow Algorithm for Detecting All Pairs of Statements that May Happen in Parallel

Information about which pairs of statements in a concurrent program can execute in parallel is important for optimizing and debugging programs, for detecting anomalies, and for improving the accuracy of dataflow analysis. In this paper, we describe a new data flow algorithm that finds a conservative approximation of the set of all such pairs. We have carried out an initial comparison of the precision of our algorithm and that of the most precise of the earlier approaches, Masticola and Ryder's non-concurrency analysis [8], using a sample of 147 concurrent Ada programs that includes the collection assembled by Masticola. For these examples, our algorithm was almost always more precise than non-concurrency analysis, in the sense that the set of pairs identified by our algorithm as possibly happening in parallel is a proper subset of the set identified by non-concurrency analysis. In 123 cases, we were able to use reachability analysis to determine exactly the set of pairs of statements t..