Usage-based RTL subsetting for hardware accelerators

Recent years have witnessed increasing use of domain-specific accelerators in computing platforms to provide power-performance efficiency for emerging applications. To increase their applicability within the domain, these accelerators tend to support a large set of functions, e.g. Nvidia s open-source Deep Learning Accelerator, NVDLA, supports five distinct groups of functions [17]. However, an individual use case of an accelerator may utilize only a subset of these functions. The unused functions lead to unnecessary overhead of silicon area, power, and hardware verification/hardware-software co-verification complexity. This motivates our research question: Given an RTL design for an accelerator and a subset of functions of interest, can we automatically extract a subset of the RTL that is sufficient for these functions and sequentially equivalent to the original RTL? We call this the Usage-based RTL Subsetting problem, referred to as the RTL subsetting problem in short. We first formally define this problem and show that it can be formulated as a program synthesis problem, which can be solved by performing expensive hyperproperty checks. To overcome the high cost, we propose multiple levels of sound over-approximations to construct an effective algorithm based on relatively less expensive temporal property checking and taint analysis for information flow checking. We demonstrate the acceptable computation cost and the quality of the results of our algorithm through several case studies of accelerators from different domains. The applicability of our proposed algorithm can be seen in its ability to subset the large NVDLA accelerator (with over 50,000 registers and 1,600,000 gates) for the group of convolution functions, where the subset reduces the total number of registers by 18.6% and the total number of gates by 37.1%.