Instruction Selection for Subword Level Parallelism Optimizations for Application Specific Instruction Processors

Application Specific Instruction Processors (or, ASIPs) have the potential to meet the high-performance demands of multimedia applications, such as image processing, audio and video encoding, speech processing, and digital signal processing. To achieve lower cost and efficient energy for high performance embedded systems built by ASIPs, subword parallelism optimization will become an important alternative to accelerate multimedia applications. But one major problem is how to exploit subword parallelism for ASIPs with limited resources. This paper shows that loop transformations such as loop unrolling, variable expansion, etc., can be utilized to create opportunities for subword parallelism, and presents a novel approach to recognize and extract subword parallelism based on Cost Subgragh (or, CSG). This approach is evaluated on Transport Triggered Architecture (TTA), a customizable processor architecture that is particularly suitable for tailoring the hardware resources according to the requirements of the application. In our experiment, 63.58% of loops and 85.64% of instructions in these loops can exploit subword parallelism. The results indicate that significant available subword parallelism would be attained using our method.