A compilation technique for software pipelining of loops with conditional jumps

Abstract

We describe a compilation algorithm for efficient software pipelining of general inner loops, where the number of iterations and the time taken by each iteration may be unpredictable, due to arbitrary if-then-else statements and conditional exit statements within the loop. As our target machine, we assume a wide instruction word architecture that allows multi-way branching in the form of if-then-else trees, and that allows conditional register transfers depending on where the microinstruction branches to (a hardware implementation proposal for such a machine is briefly described in the paper). Our compilation algorithm, which we call the pipeline scheduling technique, produces a software-pipelined version of a given inner loop, which allows a new iteration of the loop to begin on every cycle whenever dependences and resources permit. The correctness and termination properties of the algorithm are studied in the paper.