Performance of a SystemVerilog Sudoku Solver with VCS

Constrained random verification relies on efficient generation of random values according to constraints provided. As constraint solver metrics are not easily determined, usually solver efficiency can only be measured per-project and late in the verification cycle. In this paper we dissect several SystemVerilog based Sudoku puzzle solvers and compare their efficiency with the VCS constraint solver. Further, we compare efficiency between constraints applied over object instance hierarchies (game board is object oriented) versus flat constraints (game board is fully contained within a single class). Finally, we compare both approaches with several optimizations in the Sudoku solver. The common Sudoku game board is a 9x9 grid yielding approximately 2,349 constraint clauses to solve. We show that VCS can solve grid sizes up to 49x49 with 357,749 clauses. While each clause is a simple inequality, the size of the constraint formula to solve and its structure provides valuable feedback on the solvers efficiency.