Reducing code size for heterogeneous-connectivity-based VLIW DSPs through synthesis of instruction set extensions

Abstract

VLIW DSP architectures exhibit heterogeneous connections between functional units and register files for speeding up special tasks. Such architectural characteristics can be effectively exploited through the use of complex instruction set extensions (ISEs). Although VLIWs are increasingly being used for DSP applications to achieve very high performance, such architectures are known to suffer from increased code size. This paper addresses how to generate ISEs that can result in significant code size reduction in VLIW DSPs without degrading performance. Unfortunately, contemporary techniques for instruction set synthesis fail to extract legal ISEs for heterogeneous-connectivity-based architectures. We propose a Heuristic-based algorithm to synthesize ISEs for a generalized heterogeneous-connectivity-based VLIW DSP architecture. We achieve an average code size reduction of 25% on the MiBench suite with no penalty in performance by applying our ISE generation algorithm on the TI TMS320C6xx, a representative VLIW DSP.