Some Experiments in Local Microcode Compaction for Horizontal Machines

Microcode compaction is an essential tool for the compilation of high-level language microprograms into microinstructions with parallel microoperations. The purpose of the research reported in this paper is to compare four microcode compaction methods reported in the literature: first-come first-served, critical path, branch and bound, and list scheduling. In order to do this a complete, machine independent method of representing the microoperations of real machines had to be developed; and the compaction algorithms had to be recast to use this representation. The compaction algorithms were then implemented and tested on microcode produced by a compiler for a high-level microprogramming language. The results of these experiments were that for all cases examined the first-come first-served and list scheduling algorithms produced microcode compacted into a minimal number of microinstructions in time that was a polynomial function of order two of the number of input microoperations.