High-Level Synthesis of Non-Rectangular Multi-Dimensional Nested Loops Using Reshaping and Vectorization

High-Ievel synthesis accelerates the process of design space exploration in which various transformations and optimizations can be applied to the high-level description. In this paper, a new method has been proposed to improve the high-level synthesis process for non-rectangular multi-dimensional nested loops using reshaping and vectorization techniques. As the high-level descriptions with non-rectangular iteration spaces do not lend themselves well to efficient high-level synthesis process, our method proposes a reshaping technique to convert nonrectangular iteration spaces with certain inter-iteration dependencies to the rectangular ones. Furthermore, the proposed method suggests a vectorization technique to let the different iterations be executed simultaneously in a manner which does not violate inter-iteration dependencies. Finally, this paper combines the proposed reshaping and vectorization techniques to a hybrid method which supports both 2D and 3D perfect/imperfect nested loops and can be extended for the nested loops of dimensions more than three. According to the experimental results, the proposed hybrid method shows average speed-up of 51.9%, 50.1%, and 15.9% in comparison with the state-of-the-art methods for the pipelined perfect, the pipelined imperfect, and the pipelined 3D nested loops, respectively.