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Register Allocation by Graph Coloring

An undirected graph is colored by assigning a ``color'' to each node, such that no two nodes that are connected have the same color.

Graph coloring is applied to register assignment in the following way:

A heuristic algorithm is applied to find approximately the minimum number of colors needed to color the graph. If this is more than the number of available registers, spill code is added to reduce the number of colors needed.

By keeping as many variables as possible in registers, the code can be significantly improved.