CalCS: SMT solving for non-linear convex constraints

Certain formal verification tasks require reasoning about Boolean combinations of non-linear arithmetic constraints over the real numbers. In this paper, we present a new technique for satisfiability solving of Boolean combinations of non-linear constraints that are convex. Our approach applies fundamental results from the theory of convex programming to realize a satisfiability modulo theory (SMT) solver. Our solver, CalCS, uses a lazy combination of SAT and a theory solver. A key step in our algorithm is the use of complementary slackness and duality theory to generate succinct infeasibility proofs that support conflict-driven learning. Moreover, whenever non-convex constraints are produced from Boolean reasoning, we provide a procedure that generates conservative approximations of the original set of constraints by using geometric properties of convex sets and supporting hyperplanes. We validate CalCS on several benchmarks including formulas generated from bounded model checking of hybrid automata and static analysis of floating-point software.