SRDAG compaction: a generalization of trace scheduling to increase the use of global context information

Microcode compaction is the process of converting essentially vertical microcode into horizontal microcode for a given architecture. The conventional plan calls for a microcode compiler to generate vertical code for a given architecture and then use a compaction system to produce horizontal code, thereby greatly reducing the complexity of horizontal code generation.This paper attempts to extend the existing techniques used to perform the compaction process. Specifically, the procedure presented generalizes the "trace scheduling" method of [Fisher81] by using more global context information in compaction decisions. A number of definitions from classical compaction are generalized to encompass this expanded scope.Further, the paper presents two example classes of problem for which the new method outperforms the trace scheduling technique in terms of the execution time efficiency of the generated code. A number of unresolved questions are noted involving the class of global compaction procedures.