A polynomial spilling heuristic: Layered allocation

Register allocation is one of the most important, and one of the oldest compiler optimizations. It aims to map temporary variables to machine registers, and defaults to explicit load/store from memory when necessary. The latter option is referred to as spilling. This paper addresses the minimization of the spill code overhead, one of the difficult problems in register allocation. We devised a heuristic, polynomial approach called layered. It is rooted in the recent advances in decoupled register allocation. As opposed to conventional incremental spilling, our method incrementally allocates clusters of variables. We demonstrate its quasi-optimiality on standard benchmarks and on two architectures.