Improving polyhedral code generation for high-level synthesis

Wei Zuo, Peng Li, Deming Chen, Louis-Noël Pouchet, Shunan Zhong, Jason Cong

Abstract: High-level synthesis (HLS) tools are now capable of generating high-quality RTL codes for a number of programs. Nevertheless, for best performance aggressive program transformations are still required to exploit data reuse and enable communication/computation overlap. The polyhedral compilation framework has shown great promise in this area with the development of HLS-specific polyhedral transformation techniques and tools. However, all these techniques rely on polyhedral code generation to translate a schedule for the program's operations into an actual C code that is input to the HLS tool. In this work we study the changes to the state-of-the-art polyhedral code generator CLooG which are required to tailor it for HLS purposes. In particular, we develop various techniques to significantly improve resource utilization on the FPGA. We also develop a complete technique geared towards effective code generation of rectangularly tiled code, leading to further improvements in resource utilization. We demonstrate our techniques on a collection of affine benchmarks, reducing by 2x on average (up to 10x) the area used after high-level synthesis.