A Small, Fast and Low-Power Register File by Bit-Partitioning

Abstract

A large multi-ported register file is indispensable for exploiting instruction level parallelism (ILP) in today's dynamically scheduled superscalar processors. The number of ports and the size of the register file must be enlarged as the issue width and instruction window size increase. However, a larger register file causes longer access delays and more power consumption. To tackle these problems, we propose bit-partitioned register file which reduces the area, access time, and energy consumption of the register file. The proposed method relies on the fact that many operands do not need the full-bit width (typically a 32-bit or 64-bit width) of a register entry. Because the effective bit-width of most register operands is narrower than the full-bit width of a register entry, the upper bits of the register entries assigned to such narrow-width operands are useless. Thus, we propose to use of these useless upper bits for other operands by partitioning the register entries. In this paper, we show the mechanism of the proposed register file and evaluate its performance and power consumption. The evaluation results reveal that the proposed register file achieves higher instruction per cycle (IPC) in a smaller physical area, and consequently with shorter access time and less power consumption.