Convex Invariant Refinement by Control Node Splitting: a Heuristic Approach

To improve the accuracy of invariants found when analyzing a transition system, we introduce an original rewriting heuristic of control flow graphs, based on a control node splitting algorithm. The transformation preserves the program behaviors, whilst allowing a finer analysis.We have carried out experiments with PIPS, a source-to-source compiler, and Aspic, an abstract interpretation tool, using 71 test cases published by Gonnord, Gulwani, Halbwachs, Jeannet & al. The number of invariants found by these tools goes up from 28 to 69 for PIPS and from 44 to 62 for Aspic when our heuristics is used as a preprocessing step. The total execution time of PIPS is only marginally increased, going up from 76 to 103s, thus showing the practical interest of our optimization technique.