A new fast algorithm for optimal register allocation in modulo scheduled loops

Theme 1 - Reseaux et systemes - Projet A3SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : 14802 E, issue : a.1998 n.3337 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

A New Fast Algorithm for Optimal Register Allocation in Modulo Scheduled Loops

In this paper, we focus on the register allocation phase of software pipelining. We are interested in optimal register allocation. This means that the number of registers used must be equal to the maximum number of simultaneously alive variables of the loop. Usually two different means are used to achieve this, namely register renaming or loop unrolling. As these methods have both drawbacks, we introduce here a solution which is a trade-off between inserting move operations and unrolling the loop. We present a new algorithmic framework of optimal register allocation for modulo scheduled loops. The proposed algorithm, called U&M, is simple and efficient. We have implemented it in MOST (Modulo Scheduling Toolset). An experimental study of our algorithm on more than 1000 loops has been performed and we report a summary of the main results. This new algorithm, that combines loop unrolling and register renaming, performs consistently better than several other existing methods