We introduce improvements in the algorithm by Gastin and Oddoux translating LTL formulae into Büchi automata via very weak alternating co-Büchi automata and generalized Büchi automata. Several improvements are based on specific properties of any formula where each branch of its syntax tree contains at least one eventually operator and at least one always operator. These changes usually result in faster translations and smaller automata. Other improvements reduce non-determinism in the produced automata. In fact, we modified all the steps of the original algorithm and its implementation known as LTL2BA. Experimental results show that our modifications are real improvements. Their implementations within an LTL2BA translation made LTL2BA very competitive with the current version of SPOT, sometimes outperforming it substantially.

We propose a flexible exchange format for ω-automata, as typically used in formal verification, and implement support for it in a range of established tools. Our aim is to simplify the interaction of tools, helping the research community to build upon other people's work. A key feature of the format is the use of very generic acceptance conditions, specified by Boolean combinations of acceptance primitives, rather than being limited to common cases such as Büchi, Streett, or Rabin. Such flexibility in the choice of acceptance conditions can be exploited in applications, for example in probabilistic model checking, and furthermore encourages the development of acceptance-agnostic tools for automata manipulations. The format allows acceptance conditions that are either state-based or transition-based, and also supports alternating automata.

Abstract. We introduce asynchronous dynamic pushdown networks (ADPN), a new model for multithreaded programs in which pushdown systems communicate via shared memory. ADPN generalizes both CPS (concurrent pushdown systems) [7] and DPN (dynamic pushdown networks) [5]. We show that ADPN exhibit several advantages as a program model. Since the reachability problem for ADPN is undecidable even in the case without dynamic creation of processes, we address the bounded reachability problem [7], which considers only those computation sequences where the (index of the) thread accessing the shared memory is changed at most a fixed given number of times. We provide efficient algorithms for both forward and backward reachability analysis. The algorithms are based on automata techniques for symbolic representation of sets of configurations.

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We present a symbolic execution based algorithm that for a given program and a given program location produces a nontrivial necessary condition on input values to drive the program execution to the given location. We propose a usage of the produced condition in contemporary bug finding and test generation tools based on symbolic execution. Experimental results indicate that the presented technique can significantly improve performance of the tools.