Optimal software pipelining of loops with control flows

Software pipelining is widely used as a compiler optimization technique to achieve high performance in machines that exploit instruc-tion-level parallelism. However, surprisingly, there have been few theoretical or empirical results on optimal software pipelining of loops with control flows. In this paper, we present three new contributions for this under-investigated problem. First, we propose a necessary and sufficient condition for a loop with control flows to have an optimally software-pipelined program. We also present a decision procedure to compute the condition. Second, we present two software pipelining algorithms. The first algorithm computes an optimal solution for every loop satisfying the condition, but may run in exponential time. The second algorithm computes optimal solutions efficiently for most (but not all) loops satisfying the condition. Third, we present experimental results which strongly indicate that achieving the optimality in the software-pipelined programs is a viable goal in practice with realistic hardware support.