Low-level Loop Analysis and Pipelining of Applications mapped to Xilinx FPGAs

In this paper we investigate using low-level loop analysis to identify common loop patterns in the netlist generated by the synthesis flow and use loop optimization techniques to increase Fmax of applications implemented on Xilinx FPGAs. Ordinarily, feed-forward paths in the netlist can be easily pipelined. The focus of this study is only sequential loops (with feedback cycles) that are more challenging to optimize. We show that, using low-level loop analysis, we can improve Fmax on average by 57% and achieve an average Fmax of 714MHz across seven industrial designs. Using aggressive loop combining, we also show that we can save 18% area on average while still improving the Fmax by 15% to 41% on four of the seven designs.