Dynafuse: dynamic dependence analysis for FPGA pipeline fusion and locality optimizations

Abstract

Although high-level synthesis improves FPGA productivity by enabling designers to use high-level code, the resulting performance is often significantly worse than register-transfer-level designs. One cause of such limited optimization is that high-level synthesis tools are restricted by multiple possible dependencies due to the undecidability of alias analysis. In this paper, we introduce the Dynafuse optimization, which analyzes dependencies dynamically to resolve aliases and enable runtime circuit optimizations. To resolve aliases, Dynafuse provides a specialized software data structure that dynamically determines definition-use chains between FPGA functions. In addition, Dynafuse statically creates a reconfigurable overlay network that uses detected dependencies to dynamically adjust connections between functions and memories in order to fuse pipelines and exploit data locality. Experimental results show that Dynafuse sped up two existing FPGA applications by 1.6-1.8x when exploiting locality and by 3-5x when fusing pipelines. Furthermore, the speedup from pipeline fusion increases linearly with the number of fused functions, which suggests larger applications will experience larger improvements.