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Sliding Tile Puzzles
(2021)
CleanMaple
(2021)
Conflict Driven Clause Learning (CDCL) SAT solvers spend most of their execution time iterating through clauses in unit propagation. Efficient implementations of unit propagation mostly rely on the two watched literals (TWL) scheme, a specialised data structure watching two literals per clause to prevent as many clause lookups as possible. In this paper, we present Priority Propagation (PriPro)—a minimally invasive method to adapt unit propagation in existing SAT solvers. With PriPro the traditional TWL scheme is partitioned to allow for rearranging the order in which clauses are examined. This is used to achieve a prioritisation of certain clauses. Using PriPro in combination with a dynamic heuristic to prioritise resolvents from recent conflicts, the effectiveness of unit propagation can be increased. In the state-of-the-art CDCL SAT solver CaDiCaL modified to use PriPro, we obtained a 5–10 % speedup on the SAT Competition 2021 benchmark set in a fair comparison with the unmodified CaDiCaL.