In-place vs. copy-on-write CEGAR refinement for block summarization with caching

Abstract

Block summarization is an efficient technique in software verification to decompose a verification problem into separate tasks and to avoid repeated exploration of reusable parts of a program. In order to benefit from abstraction at the same time, block summarization can be combined with counterexample-guided abstraction refinement (CEGAR). This causes the following problem: whenever CEGAR instructs the model checker to refine the abstraction along a path, several block summaries are affected and need to be updated. There exist two different refinement strategies: a destructive in-place approach that modifies the existing block abstractions and a constructive copy-on-write approach that does not change existing data. While the in-place approach is used in the field for several years, our new approach of copy-on-write refinement has the following important advantage: A complete exportable proof of the program is available after the analysis has finished. Due to the benefit from avoiding recomputations of missing information as necessary for in-place updates, the new approach causes almost no computational overhead overall. We perform a large experimental evaluation to compare the new approach with the previous one to show that full proofs can be achieved without overhead.