The Bene t of Predicated Execution for Software Pipelining

Software pipelining is a compile-time scheduling technique that overlaps successive loop iterations to expose operation-level parallelism. An important problem with the development of e ective software pipelining algorithms is how to handle loops with conditional branches. Conditional branches increase the complexity and decrease the e ectiveness of software pipelining algorithms by introducing many possible execution paths into the scheduling scope. This paper presents an empirical study of the importance of an architectural support, referred to as predicated execution, on the e ectiveness of software pipelining. In order to perform an in-depth analysis, we focus on Rau's modulo scheduling algorithm for software pipelining. Three versions of the modulo scheduling algorithm, one with and two without predicated execution support, are implemented in a prototype compiler. Experiments based on important loops from numeric applications show that predicated execution support substantially improves the e ectiveness of the modulo scheduling algorithm.