Tempranillo: Non-Speculative Early Register Release

Limited by the breakdown of technology scaling, CPU architects are looking for creative solutions to deliver performance improvements while unable to traditionally scale up microarchitectural structures. One promising approach is engineering a microarchitecture that uses resources more efficiently, for example, by recycling them faster to relieve pressure on critical structures and making them look bigger than they are. The physical register file (PRF) is a key structure that faces severe area and power constraints that limit its (and the whole CPU's) scalability. Based on this observation, previous work proposed solutions to reduce the pressure on the PRF by reducing the time each register remains allocated. In this paper, we corroborate earlier findings that the early release of registers is a promising approach to reduce the occupancy of the PRF and we identify novel tight conditions for safely releasing registers. Based on this analysis, we design Tempranillo: an aggressive, non-speculative microarchitecture to release registers as early as possible without requiring additional recovery mechanisms. Tempranillo delivers up to 3.3 % and 11.8 % performance improvement over conventional release on singlethreaded and a 2 -way SMT CPUs, respectively. Additionally, Tempranillo requires modest storage overheads, translating into a performance improvement per KiB of storage of up to 2.6 % and 9.3 % for single-thread and 2-way SMT, respectively. Our evaluation shows that Tempranillo improves over both the state-of-the-art non-speculative and speculative proposals.