Software Pipelining

Abstract

Pipelining and parallel functional units are common optimization techniques used in high-performance processors. Traditionally, this parallelism internal to the data path of a processor is only available to the microcode programmer, and the problems of minimizing the execution time of the microcode within and across basic blocks are known as local and global compaction, respectively. The development of the global compaction technique, trace scheduling, has led to the introduction of VLIW (very long instruction word) architectures [9,19,20,21]. A VLIW machine is like a horizontally microcoded machine: it consists of parallel functional units, each of which can be independently controlled through dedicated fields in a “very long” instruction. A characteristic distinctive of VLIW architectures is that these long instructions are the machine instructions. There is no additional layer of interpretation where machine instructions are expanded into micro-instructions. A compiler directly generates these long machine instructions from programs written in a high-level language. A VLIW machine generally has an orthogonal instruction set; whereas in a typical horizontally microcoded engine, complex resource or field conflicts exist between functionally independent operations.