GRIT: Guy’s RISC Implementation of the Three Instruction Machine

Abstract

Fairbaim and Wray’s Three Instruction Machine [1, 2] has been one of the most influential lazy abstract machine designs in recent years. However, despite its influence, some of the finer details of the implementation technique remain unclear. We hope this paper will help clarify these details. Taking Fairbaim and Wray’s Normal Order version of the TIM as a starting point the author has produced two improved TIMs: the G-TIM [3], a simple single stack version; and the A-TIM [4], a more ambitious two stack design. In order to simplify the comparison between the two new TIMs and the original, they are compiled down to µTIM, a RISC microcode for TIMs, which is ultimately translated to native code. The resulting implementation, called GRIT (Guy’s RISC Implementation of the Three Instruction Machine), incorporates several novel techniques which simplify the design of the compiler but still produce good quality code. In this paper we describe these techniques and demonstrate that, despite being simpler, they result in performance at least as good as that of the Chalmers’ implementation of the G-machine [5, 6, 7].