An instruction set and microarchitecture for instruction level distributed processing

Abstract

An instruction set architecture (ISA) suitable for future microprocessor design constraints is proposed. The ISA has hierarchical register files with a small number of accumulators at the top. The instruction stream is divided into chains of dependent instructions (strands) where intra-strand dependences are passed through the accumulator. The general-purpose register file is used for communication between strands and for holding global values that have many consumers.A microarchitecture to support the proposed ISA is proposed and evaluated. The microarchitecture consists of multiple, distributed processing elements. Each PE contains an instruction issue FIFO, a local register (accumulator) and local copy of register file. The overall simplicity, hierarchical value communication, and distributed implementation will provide a very high clock speed and a relatively short pipeline while maintaining a form of superscalar out-of-order execution.Detailed timing simulations using translated program traces show the proposed microarchitecture is tolerant of global wire latencies. Ignoring the significant clock frequency advantages, a microarchitecture that supports a 4-wide fetch/decode pipeline, 8 serial PEs, and a two-cycle inter-PE communication latency performs as well as a conventional 4-way out-of-order superscalar processor.