Improving Energy Efficiency and Reducing Code Size with RISC

Delivering the instruction stream can be the largest source of energy consumption in a processor, yet loosely-encoded RISC instruction sets are wasteful of instruction bandwidth. Aiming to improve the performance and energy efficiency of the RISC-V ISA, this thesis proposes RISC-V Compressed (RVC), a variable-length instruction set extension. RVC is a superset of the RISC-V ISA, encoding the most frequent instructions in half the size of a RISCV instruction; the remaining functionality is still accessible with full-length instructions. RVC programs are 25% smaller than RISC-V programs, fetch 25% fewer instruction bits than RISCV programs, and incur fewer instruction cache misses. Its code size is competitive with other compressed RISCs. RVC is expected to improve the performance and energy per operation of RISC-V.