Efficient High-Level Synthesis for Nested Loops of Nonrectangular Iteration Spaces

Most existing solutions to pipelining nested loops are developed for general purpose processors, and may not work efficiently for field-programmable gate arrays due to loop control overhead. This is especially true when the nested loops have nonrectangular iteration spaces (IS). Thus we propose a novel method that can transform triangular IS—the most frequently found type of nonrectangular IS—into rectangular ones, so that other loop transformations can be effectively applied and the overall performance of nested loops can be maximized. Our evaluation results using the state-of-the-art Vivado high-level synthesis tool demonstrate that our technique can improve the performance of nested loops with nonrectangular IS significantly.