Hare: a Hierarchical Allocator for Registers in Multiple Issue Architectures

In this paper we present HARE, a new hierarchical approach to register allocation and assignment for multiple issue load/store architectures. HARE makes extensive use of execution estimates and functional unit availability information to select values for spilling and to place the spill code in locations that minimize the increase in the overall execution time of the program. Incorporated in HARE is recursive allocation, a new hierarchical allocation technique that compares the costs of spilling registers in a code region with reducing the number of registers used in subregions by spilling additional values. HARE also makes improvements in the register allocation techniques of coalescing, rematerialization, and register copy instructions.