Redundant operator creation: a scheduling optimization technique

A method is proposed for optimizing a Control I Data Flow Graph (CDFG), to generate shorter schedules, given a fmed number of functional units. A counter-intuitive approach is taken of adding more operations to the CDFG to reduce the number of cycles in the final schedule. In this paper, this technique is applied to individual straight-line code sections (stateblocks) to reduce their execution times (as opposed to recently published methods for optimizations that transcend state block boundaries). In many cases this technique has produced schedules significantly better (up to 30%) than those previously published. The algorithm rearranges the CDFG, modifring the syntactical structure, while preserving the semantic meaning. The focus of attack is on the critical path, where most of the tramJormations are attempted to decrease the length of the critical path and hence the length of the resultant CDFG. The benchmark were run on a MIPS RC3240 Riscomputer (-18 MIPS) and each schedule was derived at in less than I CPU second!

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