An Analysis of Graph Coloring Register Allocation

Graph coloring is the de facto standard technique for register allocation within a compiler. In this paper we examine the importance of the quality of the coloring algorithm and various extensions of the basic graph coloring technique by replacing the coloring phase of the GNU compiler’s register allocator with an optimal coloring algorithm. We then extend this optimal algorithm to incorporate various extensions such as coalescing and preferential register assignment. We find that using an optimal coloring algorithm has surprisingly little benefit and empirically demonstrate the benefit of the various extensions. This research was sponsored in part by the National Science Foundation under grant CCR-0205523 and in part by the Defense Advanced Research Project Agency (DARPA) under contracts N000140110659 01PR07586-00 and MDA972-01-3-0005. Any opinions, findings and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect those of the sponsors.