On Complexity Bounds and Confluence of Parallel Term Rewriting
This work provides a practical method for analyzing parallel runtime complexity of term rewriting systems, benefiting researchers and tool developers in automated program analysis.
The paper introduces automatic techniques for deriving upper and lower bounds on parallel complexity of parallel-innermost term rewriting, leveraging existing sequential complexity methods. Experiments with the tool AProVE demonstrate the approach's applicability and precision on numerous benchmarks.
We revisit parallel-innermost term rewriting as a model of parallel computation on inductive data structures and provide a corresponding notion of runtime complexity parametric in the size of the start term. We propose automatic techniques to derive both upper and lower bounds on parallel complexity of rewriting that enable a direct reuse of existing techniques for sequential complexity. Our approach to find lower bounds requires confluence of the parallel-innermost rewrite relation, thus we also provide effective sufficient criteria for proving confluence. The applicability and the precision of the method are demonstrated by the relatively light effort in extending the program analysis tool AProVE and by experiments on numerous benchmarks from the literature.