Local Microcode Compaction Techniques

Abstract

Microcode compaction is an essential tool for the compilation of high-level language microprograms into microinstructions with parallel microoperations. Although guaranteeing minimum execution time is an exponentially complex problem, recent research indicates that it is not difficult to obtain practical results. This paper, which assumes no prior knowledge of microprogramming on the part of the reader, surveys the approaches that have been developed for compacting microcode. A comprehensive terminology for the area is presented, as well as a general model of processor behavior suitable for comparing the algorithms. Execution examples and a discussion of strengths and weaknesses are given for each of the four classes of loc .al compaction algorithms: linear, critical path, branch and bound, and list scheduling. Local compaction, which applies to jump-free code, is fundamental to any compaction technique. The presentation emphasizes the conceptual distinction between data dependency and conflict analysis.