A Conservative Data Flow Algorithm for Detecting All Pairsof

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 data ow analysis. In this paper, we describe a new data ow algorithm that nds 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, Masti-cola and Ryder's non-concurrency analysis 8], using a sample of 159 concurrent Ada programs that includes the collection assembled by Masticola and Ryder. For these examples, our algorithm was almost always more precise than non-concurrency analysis, in the sense that the set of pairs identiied by our algorithm as possibly happening in parallel is a proper subset of the set identiied by non-concurrency analysis. In 132 cases, we were able to use reachability analysis to determine exactly the set of pairs of statements that may happen in parallel. For these cases, there were a total of only 10 pairs identiied by our algorithm that cannot actually happen in parallel.