Characterization of program loops in code optimization

Recent work in code optimization has led to development of new unified optimizing transformations[6,7]. Application of these transformations requires solution of bi-directional data flow problems over program flow graphs using iterative solution techniques. Appropriate characterization of program loops in the flow graph is necessary so as (i) not to hinder code movement, etc., and (ii) restrict optimization overheads to low levels. This paper reviews alternate loop characterizations and proposes a characterization which leads to minimum overheads and has certain nice properties from a practical viewpoint.