Enhanced Modulo Scheduling for Loops with Conditional

Loops with conditional branches have multiple execution paths which are diicult to software pipeline. The mod-ulo scheduling technique for software pipelining addresses this problem by converting loops with conditional branches into straight-line code before scheduling. In this paper we present an Enhanced Modulo Scheduling (EMS) technique that can achieve a lower minimum Initiation Interval than modulo scheduling techniques that rely on either Hierarchical Reduction or If-conversion with Predicated Execution. These three modulo scheduling techniques have been implemented in a prototype compiler. We show that for existing architectures which support one branch per cycle, EMS performs approximately 18% better than Hierarchical Reduction. We also show that If-conversion with Predicated Execution outperforms EMS assuming one branch per cycle. However, with hardware support for multiple branches per cycle, EMS should perform as well as or better than If-conversion with Predicated Execution.