Enhancing Predicate Pairing with Abstraction for Relational Verification

Relational verification is a technique that aims at proving properties that relate two different program fragments, or two different program runs. It has been shown that constrained Horn clauses (CHCs) can effectively be used for relational verification by applying a CHC transformation, called predicate pairing, which allows the CHC solver to infer relations among arguments of different predicates. In this paper we study how the effects of the predicate pairing transformation can be enhanced by using various abstract domains based on linear arithmetic (i.e., the domain of convex polyhedra and some of its subdomains) during the transformation. After presenting an algorithm for predicate pairing with abstraction, we report on the experiments we have performed on over a hundred relational verification problems by using various abstract domains. The experiments have been performed by using the VeriMAP transformation and verification system, together with the Parma Polyhedra Library (PPL) and the Z3 solver for CHCs.Comment: Pre-proceedings paper presented at the 27th International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR 2017), Namur, Belgium, 10-12 October 2017 (arXiv:1708.07854

Using Relational Verification for Program Slicing

Program slicing is the process of removing statements from a program such that defined aspects of its behavior are retained. For producing precise slices, i.e., slices that are minimal in size, the program\u27s semantics must be considered. Existing approaches that go beyond a syntactical analysis and do take the semantics into account are not fully automatic and require auxiliary specifications from the user. In this paper, we adapt relational verification to check whether a slice candidate obtained by removing some instructions from a program is indeed a valid slice. Based on this, we propose a framework for precise and automatic program slicing. As part of this framework, we present three strategies for the generation of slice candidates, and we show how dynamic slicing approaches - that interweave generating and checking slice candidates - can be used for this purpose. The framework can easily be extended with other strategies for generating slice candidates. We discuss the strengths and weaknesses of slicing approaches that use our framework

Regression Verification for Programmable Logic Controller Software

Automated production systems are usually driven by Programmable Logic Controllers (PLCs). These systems are long-living - yet have to adapt to changing requirements over time. This paper presents a novel method for regression verification of PLC code, which allows one to prove that a new revision of the plant\u27s software does not break existing intended behavior. Our main contribution is the design, implementation, and evaluation of a regression verification method for PLC code. We also clarify and define the notion of program equivalence for reactive PLC code. Core elements of our method are a translation of PLC code into the SMV input language for model checkers, the adaptation of the coupling invariants concept to reactive systems, and the implementation of a toolchain using a model checker supporting invariant generation. We have successfully evaluated our approach using the Pick-and-Place Unit benchmark case study

Equivalence checking of static affine programs using widening to handle recurrences

Designers often apply manual or semi-automatic loop and data transformations on array and loop intensive programs to improve performance. It is crucial that such transformations preserve the functionality of the program. This paper presents an automatic method for constructing equivalence proofs for the class of static affine programs. The equivalence checking is performed on a dependence graph abstraction and uses a new approach based on widening to find the proper induction hypotheses for reasoning about recurrences. Unlike transitive closure based approaches, this widening approach can also handle non-uniform recurrences. The implementation is publicly available and is the first of its kind to fully support commutative operations.status: publishe

Equivalence checking of static affine programs using widening to handle recurrences

Designers often apply manual or semi-automatic loop and data transformations on array and loop intensive programs to improve performance. The transformations should preserve the functionality, however, and this paper presents an automatic method for constructing equivalence proofs for the class of static affine programs. The equivalence checking is performed on a dependence graph abstraction and uses a new approach based on widening to find the proper induction hypotheses for reasoning about recurrences. Unlike transitive closure based approaches, this widening approach can also handle non-uniform recurrences. The implementation is publicly available and is the first of its kind to fully support commutative operations.nrpages: 31status: publishe