On Data Parallelism Code Restructuring for HLS Targeting FPGAs

FPGAs have emerged as hardware accelerators, and in the last decade, researchers have proposed new languages and frameworks to improve the efficiency when mapping computations to FPGAs. One of the main tasks when considering the mapping of software code to FPGAs is code restructuring. Code restructuring is of paramount importance to achieve efficient FPGA-based accelerators, and its automation continues to be a challenge. This paper describes our recent work on techniques to automatically restructure and annotate C code with directives optimized for HLS targeting FPGAs. The input of our approach consists of an unfolded dataflow graph (DFG), currently obtained by a trace of the program’s execution, and restructured C code with HLS directives as output. Specifically, in this paper we propose algorithms to optimize the input DFGs and use isomorphic graph detection for exposing data-level parallelism. The experimental results show that our approach is able to generate efficient FPGA implementations, with significant speedups over the input unmodified source codes, and very competitive to implementations obtained by manual optimizations and by previous approaches. Furthermore, the experiments show that, using our approach, it is possible to extract data-parallelism in linear to quadratic time with respect to the number of nodes of the input DFG.