Instruction set synthesis with efficient instruction encoding for configurable processors

Abstract

Application-specific instructions can significantly improve the performance, energy-efficiency, and code size of configurable processors. While generating new instructions from application-specific operation patterns has been a common way to improve the instruction set (IS) of a configurable processor, automating the design of ISs for given applications poses new challenges---how to create as well as utilize new instructions in a systematic manner, and how to choose the best set of application-specific instructions considering the various effects the new instructions may have on the data path and the compilation? To address these problems, we present a novel IS synthesis framework that optimizes the IS through an efficient instruction encoding for the given application as well as for the given data path architecture. We first build a library of new instructions created with various encoding alternatives taking into account the data path architecture constraints, and then select the best set of instructions while satisfying the instruction bitwidth constraint. We formulate the problem using integer linear programming and also present an effective heuristic algorithm. Experimental results using our technique generate ISs that show improvements of up to about 40% over the native IS for several application benchmarks running on typical embedded RISC processors.