A Local-Conscious Global Register Allocator for VLIW DSP Processors with Distributed Register Files

Embedded processors developed in recent years have attempted to employ novel hardware design to reduce ever-growing complexity, power dissipation, and die area. While using a distributed register file architecture with irregular accessing constraints is considered to be an effective approach rather than traditional unified register file structures, conventional compilation techniques are not adequate to utilize such new register file organizations for optimal performance. This paper presents a novel scheme for register allocation which composes of global and local register allocation, on a VLIW DSP processor with distributed register files whose port access is highly restricted. In the scheme, a sub-phase prior to original global/local register allocation, named global/local RFA (register file assignment), is introduced to minimize various register file communication costs. For featured register file structure where each cluster contains heterogeneous register files, conventional register allocation scheme with cluster assignment only have to be enhanced to cope both inter-cluster and intra-cluster communications. Due to potential but heavy influences of global RFA on local RFA, a heuristic algorithm is proposed where global RFA manages to make suitable decisions on communication for local RFA. Experiments were done with a developing compiler based on the Open Research Compiler (ORC), and the results indicate that the compilation with the proposed approach delivers significant performance improvement, comparable to the solution using only the PALF scheme developed in our previous work.