Tree compaction of microprograms

Although Fisher's trace scheduling procedure for global compaction may produce significant reduction in execution time of compacted microcode, the growth of memory size by extensive copying of blocks can be enormous. In the worst case, the memory size can grow exponentially [FIS81a] and the complex bookkeeping stage of the trace scheduling is an obstacle to implementation.A technique called tree compaction, which is based on the trace scheduling, is proposed to mitigate these drawbacks. Basically, it partitions a given set of microprogram blocks into tree-shaped subsets and applies the idea of trace scheduling on each tree-shaped subset separately. It achieves almost all of the compaction of the Fisher's trace scheduling procedure except that which causes copying of blocks. Preliminary tests indicate that tree compaction gives almost as short execution time as trace scheduling but with much less memory. The paper includes such an example.