Automatic complex instruction identification for efficient application mapping onto ASIPs

Instruction Set Customization is a well-known technique to enhance the performance and efficiency of Application-Specific Processors (ASIPs). An extensive application profiling can indicate which parts of a given application, or class of applications, are most frequently executed, enabling the implementation of such frequently executed parts in hardware as custom instructions. However, a naive ad hoc instruction set customization process may identify and select poor instruction extension candidates, which may not result in a significantly improved performance with low circuit-area and energy footprints. In this paper we propose and discuss an efficient instruction set customization method and automatic tool, which exploit the maximal common subgraphs (common operation patterns) of the most frequently executed basic blocks of a given application. The speed results from our tool for a VLIW ASIP are provided for a set of benchmark applications. The average execution time reduction ranges from 30% to 40%, with only a few custom instructions.