FLASH: foresighted latency-aware scheduling heuristic for processors with customized datapaths

Application-specific instruction set processors (ASIPs) have the potential to meet the challenging cost, performance, and power goals of future embedded processors by customizing the hardware to suit an application. A central problem is creating compilers that are capable of dealing with the heterogeneous and nonuniform hardware created by the customization process. The processor datapath provides an effective area to customize, but specialized datapaths often have nonuniform connectivity between the function units, making the effective latency of a function unit dependent on the consuming operation. Traditional instruction schedulers break down in this environment due to their locally greedy nature of binding the best choice for a single operation even though that choice may be poor due to a lack of communication paths. To effectively schedule with nonuniform connectivity, we propose a foresighted latency-aware scheduling heuristic (FLASH) that performs lookahead across future scheduling steps to estimate the effects of a potential binding. FLASH combines a set of lookahead heuristics to achieve effective foresight with low compile-time overhead.