Interpolant Learning and Reuse in SAT-Based Model Checking

Bounded Model Checking (BMC) is one of the most paradigmatic practical applications of Boolean Satisfiability (SAT). The utilization of SAT in model checking has allowed significant performance gains and, as a consequence, a large number of commercial verification tools now include SAT-based model checkers. Recent work has provided SAT-based BMC with completeness conditions, and this is generally referred to as unbounded model checking (UMC). Among the existing approaches for SAT-based UMC, the utilization of interpolants is among the most effective. Despite their success, interpolants have only been used for identifying a fixed point of the set of reachable states. This paper extends the utilization of interpolants in SAT-based model checking. This is achieved by observing that, under reasonable assumptions, interpolants can be reused, i.e. computed interpolants can be reused at later stages of the model checking process. The paper develops conditions for validity of interpolant reuse. In addition, the paper outlines a new fixed point condition, alternative to the existing interpolant-based fixed point condition. Preliminary practical experience on interpolant learning and reuse is reported.