Program equivalence checking is a fundamental problem in computer science with applications to translation validation and automatic synthesis of compiler optimizations. Contemporary equivalence checkers employ SMT solvers to discharge proof obligations generated by their equivalence checking algorithm. Equivalence checkers also involve algorithms to infer invariants that relate the intermediate states of the two programs being compared for equivalence. We present a new algorithm, called invariant-sketching, that allows the inference of the required invariants through the generation of counter-examples using SMT solvers. We also present an algorithm, called query-decomposition, that allows a more capable use of SMT solvers for application to equivalence checking. Both invariant-sketching and query-decomposition help us prove equivalence across program transformations that could not be handled by previous equivalence checking algorithms.
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