There is a fairly informative survey on the subject: https://www.osti.gov/servlets/purl/1332070 (A Survey of Techniques for Architecting and Managing GPU Register File)

An easier to read research article that's narrower in subject and seemingly more relevant to the OP: https://research.nvidia.com/sites/default/files/pubs/2012-12... ("Unifying Primary Cache, Scratch, and Register File Memories in a Throughput Processor", 2012)