Predicate abstraction refinement in thread-modular analysis

Thread-modular approach over predicate abstraction is an efficient technique for software verification of complicated real-world source code. One of the main problems in the technique is a predicate abstraction refinement in a multithreaded case. A default predicate refiner considers only a path related to one thread, and does not refine the thread-modular environment. For instance, if we have applied an effect from the second thread to the current one, then the path in the second thread to the applied effect is not refined. Our goal was to develop a more precise refinement procedure, reusing a default predicate refiner to refine both: a path in a current thread and a path to an effect in the environment. The idea is to construct a joined boolean formula from these two paths. Since some variables may be common, a key challenge is to correctly rename and equate variables in two parts of the formula to accurately represent the way threads interact. It is essential to get reliable predicates that can potentially prove spuriousness of the path. The proposed approach is implemented on top of CPAchecker framework. It is evaluated on standard SV-COMP benchmark set, and the results show some benefit. Evaluation on the real-world software does not demonstrate significant accuracy increase, as the described flaw of predicate refinement is not the only reason of false positive results. While the proposed approach can successfully prove some specific paths to be spurious, it is not enough to fully prove correctness of some programs. However, the approach has further potential for improvements.