Combining source-to-source transformations and processor instruction set extensions for the automated design-space exploration of embedded systems

Abstract

Industry's demand for flexible embedded solutions providing high performance and short time-to-market has led to the development of configurable and extensible processors. These pre-verified application-specific processors build on proven baseline cores while allowing for some degree of customization through user-defined instruction set extensions (ISE) implemented as functional units in an extended micro-architecture. The traditional design flow for ISE is based on plain C sources of the target application and, after some ISE identification and synthesis stages, a modified source file is produced with explicit handles to the new machine instructions. Further code optimization is left to the compiler. In this paper we develop a novel approach, namely the combined exploration of source-level transformations and ISE identification. We have combined automated code transformation and ISE generators to explore the potential benefits of such a combination. This applies up to 50 transformations from a selection of 70, and synthesizes ISEs for the resulting code. The resulting performance has been measured on 26 applications from the SNU-RT and UTDSP benchmarks. We show that the instruction extensions generated by automated tools are heavily influenced by source code structure. Our results demonstrate that a combination of source-level transformations and instruction set extensions can yield average performance improvements of 47%. This out performs instruction set extensions when applied in isolation, and in extreme cases yields a speedup of 2.85.

Instruction Selection

“…A compromise between flexibility and performance, ASIPs are processors whose instruction sets can be extended with additional instructions, allowing the processor to be-at least partlycustomized for the running program in order to improve code quality. The task of discovering and deciding which instructions to add is commonly referred to as the instruction set extension (ISE) problem, and there exists plenty of research on how to solve this problem (see for example [11,20,31,32,41,47,52,57,78,185,198,259,260,266,353], and see [144] for a recent survey). However, although the ISE problem can be regarded as a generalization of the instruction selection problem-the main difference is that the pattern set is no longer fixed-the prevalent approach is to treat them separately.…”

Source-to-source architecture transformation for performance optimization in BIP

“…Source-to-source transformations have been considered as a powerful means for optimizing programs [6], [15]. In contrast to conventional optimization techniques, these can be applied for deeper semantics-preserving transformations which are visible to the programmer and subject to his direction and guidance.…”