Deciding conditional termination

  • Authors:
  • Marius Bozga;Radu Iosif;Filip Konečný

  • Affiliations:
  • VERIMAG, CNRS, Gières, France;VERIMAG, CNRS, Gières, France;VERIMAG, CNRS, Gières, France and IT4Innovations Centre of Excellence, FIT BUT, Czech Republic

  • Venue:
  • TACAS'12 Proceedings of the 18th international conference on Tools and Algorithms for the Construction and Analysis of Systems
  • Year:
  • 2012

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Abstract

This paper addresses the problem of conditional termination, which is that of defining the set of initial configurations from which a given program terminates. First we define the dual set, of initial configurations, from which a non-terminating execution exists, as the greatest fixpoint of the pre-image of the transition relation. This definition enables the representation of this set, whenever the closed form of the relation of the loop is definable in a logic that has quantifier elimination. This entails the decidability of the termination problem for such loops. Second, we present effective ways to compute the weakest precondition for non-termination for difference bounds and octagonal (non-deterministic) relations, by avoiding complex quantifier eliminations. We also investigate the existence of linear ranking functions for such loops. Finally, we study the class of linear affine relations and give a method of under-approximating the termination precondition for a non-trivial subclass of affine relations. We have performed preliminary experiments on transition systems modeling real-life systems, and have obtained encouraging results.