Unroll-based register coalescing
Suhyun Kim, Soo‐Mook Moon, Jinpyo Park, Kemal Ebci̇oğlu · 2000
Aggressive instruction scheduling leaves behind many renaming copy instructions that cannot be coalesced due to interferences. These copies take resources, and more seriously, they may cause a stall if they are generated for renaming of multi-latency instructions. This paper proposes a code transformation technique based on loop unrolling which makes those copies coalescible. Two unique features of the technique are its method of determining the precise unroll amount based on an idea of extended live range, and its insertion of special bookkeeping copies at loop exits. In fact, the technique provides a more general and simpler solution for the cross-iteration register overwrite problem in software pipelining which works for loops with control flows as well as for straight-line loops. In addition, it is applicable to other optimizations including path length reduction and redundant subscripted reference elimination.