Mihály Dobos-Kovács

arXiv2025

CHCVerif: A Portfolio-Based Solver for Constrained Horn Clauses

Constrained Horn Clauses (CHCs) are widely adopted as intermediate representations for a variety of verification tasks, including safety checking, invariant synthesis, and interprocedural analysis. This paper introduces CHCVERIF, a portfolio-based CHC solver that adopts a software verification approach for solving CHCs. This approach enables us to reuse mature software verification tools to tackle CHC benchmarks, particularly those involving bitvectors and low-level semantics. Our evaluation shows that while the method enjoys only moderate success with linear integer arithmetic, it achieves modest success on bitvector benchmarks. Moreover, our results demonstrate the viability and potential of using software verification tools as backends for CHC solving, particularly when supported by a carefully constructed portfolio.

cs.SE↗

arXiv2024

Bottoms Up for CHCs: Novel Transformation of Linear Constrained Horn Clauses to Software Verification

Constrained Horn Clauses (CHCs) have conventionally been used as a low-level representation in formal verification. Most existing solvers use a diverse set of specialized techniques, including direct state space traversal or under-approximating abstraction, necessitating purpose-built complex algorithms. Other solvers successfully simplified the verification workflow by translating the problem to inputs for other verification tasks, leveraging the strengths of existing algorithms. One such approach transforms the CHC problem into a recursive program roughly emulating a top-down solver for the deduction task; and verifying the reachability of a safety violation specified as a control location. We propose an alternative bottom-up approach for linear CHCs, and evaluate the two options in the open-source model checking framework THETA on both synthetic and industrial examples. We find that there is a more than twofold increase in the number of solved tasks when the novel bottom-up approach is used in the verification workflow, in contrast with the top-down technique.

cs.LO↗