Challenges Designing for FPGAs Using High-Level Synthesis

High-Level Synthesis (HLS) tools are aimed at enabling performant FPGA designs that are authored in a high-level language. While commercial HLS tools are available today, there is still a substantial performance gap between most designs developed via HLS relative to traditional, labor intensive approaches. We report on several cases where an anticipated performance improvement was either not realized or resulted in decreased performance. These include: programming paradigm choices between data parallel vs. pipelined designs; dataflow implementations; configuration parameter choices; and handling odd data set sizes. The results point to a number of improvements that are needed for HLS tool flows, including a strong need for performance modeling that can reliably guide the compilation optimization process.