A register allocation framework based on hierarchical cyclic interval graphs

Abstract

In this paper, we present a new register allocation framework based on hierarchical cyclic interval graphs. We motivate our approach by demonstrating that cyclic interval graphs provide a feasible and effective representation to characterize sequences of live ranges of variables in successive iterations of a loop. Based on this representation we provide a new heuristic algorithm for minimum register allocation, the fat cover algorithm. In addition, we present a spilling algorithm that makes use of the extra information available in the interval graph representation. Whenever possible, it favors register floats (moving values from one register to another) over the traditional register spills (storing a spilled variable into memory). We demonstrate the effectiveness of our approach on a collection of loops by comparing the results of our algorithm to the results produced by three state-of-the-art optimizing compilers.