Solving Constrained Horn Clauses Using Dependence-Disjoint Expansions

Qi Zhou
(Georgia Institute of Technology)
David Heath
(Georgia Institute of Technology)
William Harris
(Georgia Institute of Technology; Galois Inc)

Recursion-free Constrained Horn Clauses (CHCs) are logic-programming problems that can model safety properties of programs with bounded iteration and recursion. In addition, many CHC solvers reduce recursive systems to a series of recursion-free CHC systems that can each be solved efficiently.

In this paper, we define a novel class of recursion-free systems, named Clause-Dependence Disjoint (CDD), that generalizes classes defined in previous work. The advantage of this class is that many CDD systems are smaller than systems which express the same constraints but are part of a different class. This advantage in size allows CDD systems to be solved more efficiently than their counterparts in other classes. We implemented a CHC solver named Shara. Shara solves arbitrary CHC systems by reducing the input to a series of CDD systems. Our evaluation indicates that Shara outperforms state-of-the-art implementations in many practical cases.

In Temesghen Kahsai and German Vidal: Proceedings 5th Workshop on Horn Clauses for Verification and Synthesis (HCVS 2018), Oxford, UK, 13th July 2018, Electronic Proceedings in Theoretical Computer Science 278, pp. 3–18.
Published: 12th September 2018.

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