Decidable Verification of Uninterpreted Programs

Umang Mathur, P. Madhusudan, Mahesh Viswanathan

We study the problem of completely automatically verifying uninterpreted programs---programs that work over arbitrary data models that provide an interpretation for the constants, functions and relations the program uses. The verification problem asks whether a given program satisfies a postcondition written using quantifier-free formulas with equality on the final state, with no loop invariants, contracts, etc. being provided. We show that this problem is undecidable in general. The main contribution of this paper is a subclass of programs, called coherent programs that admits decidable verification, and can be decided in PSPACE. We then extend this class of programs to classes of programs that are $k$-coherent, where $k \in \mathbb{N}$, obtained by (automatically) adding $k$ ghost variables and assignments that make them coherent. We also extend the decidability result to programs with recursive function calls and prove several undecidability results that show why our restrictions to obtain decidability seem necessary.

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