Rewriting is essential for efficient bit-vector SMT solving. The rewriting algorithm commonly used by modern SMT solvers itera-tively applies a set of ad hoc rewriting rules hard-coded into the solver to simplify the given formula at the preprocessing stage. This paper proposes an automatic approach to rewriting. The solver starts each invocation with an empty set of rewriting rules. The set is extended by applying at run-time an automatic SAT-based algorithm for new rewriting rule generation. The set of rules differs from instance to instance. We implemented our approach in the framework of an algorithm for equivalence and constant propagation, called 0-saturation, which we extended from purely propositional reasoning to bit-vector reasoning. Our approach results in a substantial performance improvement in a state-of-the-art SMT solver over various SMT-LIB families.
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