Register allocation methods of improved software pipelining for loops with conditional branches

Abstract

Improved Enhanced Modulo Scheduling (Improved EMS) is proposed as an efficient software pipelining method for loops with conditional branches. In EMS and Improved EMS, multiple pipeline kernels are generated, depending on the truth value of the condition, and the appropriate one is selected on execution at each iteration. Since these kernels have variables that live for the number of stages with different conditions mixed together, register allocation becomes difficult. In this paper, the authors discuss register allocation methods using interference graphs for EMS and improved EMS. The first method is a register allocation method using conventional interference graph which is applied to the deployed kernels. Because the interference graph becomes very large, however, in proportion to the number of kernels deployed in the method, the proposed method reduces the size of the interference graph by overlapping the graphs and improves the results of register allocation. These two methods were evaluated with approximating coloring algorithms. It was clear that allocation could be performed rapidly, and in a manner in no way inferior to the conventional method for the number of registers by the method by overlapping and reducing the size of the graphs. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 89(12): 59– 69, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20290