Using cubes of non-state variables with Property Directed Reachability

A new SAT-Based algorithm for symbolic model checking has been gaining popularity. This algorithm, referred to as “Incremental Construction of Inductive Clauses for Indubitable Correctness” (IC3) or “Property Directed Reachability” (PDR), uses information learned from SAT instances of isolated time frames to either prove that an invariant exists, or provide a counter example. The information learned between each time frame is recorded in the form of cubes of the state variables. In this work, we study the effect of extending PDR to use cubes of intermediate variables representing the logic gates in the transition relation. We demonstrate that we can improve the runtime for satisfiable benchmarks by up to 3.2X, with an average speedup of 1.23X. Our approach also provides a speedup of up to 3.84X for unsatisfiable benchmarks.