Zero-cost range splitting

Abstract

This paper presents a new optimization technique that uses empty delay slots to improve code scheduling. We are able to split live ranges for free, by inserting spill code into empty delay slots. Splitting a live range can reduce interferences with other live ranges and can sometimes free registers. Live ranges no longer interfering with the split live range can sometimes make use of the extra register.Our algorithm, as a final pass over the code, exploits empty delay slots that would remain unused if spill code was not inserted. This paper proposes a variety of optimizations that use the extra registers generated from live range splitting, including coalescing live ranges and improving code scheduling. We present an algorithm for improving code scheduling and present implementation results.