On reordering instruction streams for pipelined computers

Abstract

This paper describes a method to reorder the straight line instruction streams for pipelined computers which have one instruction issue unit but may contain multiple function units. The objective is to make the most efficient usage of the pipelines within the computer system. The input to the scheduler is the intermediate code of a compiler, and is represented by a data dependence graph (DDG). The scheduler is a kind of list scheduler. The data dependence and the pipeline effect of the function units within the system have been considered for finding a most suitable time slot for each node during reordering time. The scheduler has been implemented and several scientific application programs have been tested. The results show that in most of the cases the scheduler will achieve the optimal result. The average instruction issue rate is over 96%. As a comparison, the issue rate of an ordinary compiler is only 22%; and the issue rate of a compiler with the effect of pipeline but without reordering the instruction stream is about 45%.