Image processing and machine learning applications benefit tremendously from hardware acceleration. Existing compilers target either FPGAs, which sacrifice power and performance for programmability, or ASICs, which become obsolete as applications change. Programmable domain-specific accelerators, such as coarse-grained reconfigurable arrays (CGRAs), have emerged as a promising middle-ground, but they have traditionally been difficult compiler targets since they use a different memory abstraction. In contrast to CPUs and GPUs, the memory hierarchies of domain-specific accelerators use push memories : memories that send input data streams to computation kernels or to higher or lower levels in the memory hierarchy and store the resulting output data streams. To address the compilation challenge caused by push memories, we propose that the representation of these memories in the compiler be altered to directly represent them by combining storage with address generation and control logic in a single structure—a unified buffer. The unified buffer abstraction enables the compiler to separate generic push memory optimizations from the mapping to specific memory implementations in the backend. This separation allows our compiler to map high-level Halide applications to different CGRA memory designs, including some with a ready-valid interface. The separation also opens the opportunity for optimizing push memory elements on reconfigurable arrays. Our optimized memory implementation, the Physical Unified Buffer, uses a wide-fetch, single-port SRAM macro with built-in address generation logic to implement a buffer with two read and two write ports. It is 18% smaller and consumes 31% less energy than a physical buffer implementation using a dual-port memory that only supports two ports. Finally, our system evaluation shows that enabling a compiler to support CGRAs leads to performance and energy benefits. Over a wide range of image processing and machine learning applications, our CGRA achieves 4.7× better runtime and 3.5× better energy-efficiency compared to an FPGA.

With the slowing of Moore’s law, computer architects have turned to domain-specific hardware specialization to continue improving the performance and efficiency of computing systems. However, specialization typically entails significant modifications to the software stack to properly leverage the updated hardware. The lack of a structured approach for updating the compiler and the accelerator in tandem has impeded many attempts to systematize this procedure. We propose a new approach to enable flexible and evolvable domain-specific hardware specialization based on coarse-grained reconfigurable arrays (CGRAs). Our agile methodology employs a combination of new programming languages and formal methods to automatically generate the accelerator hardware and its compiler from a single source of truth. This enables the creation of design-space exploration frameworks that automatically generate accelerator architectures that approach the efficiencies of hand-designed accelerators, with a significantly lower design effort for both hardware and compiler generation. Our current system accelerates dense linear algebra applications but is modular and can be extended to support other domains. Our methodology has the potential to significantly improve the productivity of hardware-software engineering teams and enable quicker customization and deployment of complex accelerator-rich computing systems.

Image processing applications can benefit tremendously from FPGA acceleration. However, hardware accelerators for these applications look very different from the programs that image processing algorithm designers are accustomed to writing. As a result, many image processing hardware compilers have been designed to generate hardware accelerators from high-level specifications of image processing algorithms. Unfortunately, all of these compilers either exclude crucial access patterns, do not scale to realistic size applications, or rely on a compilation process in which each stage of the application is an independently scheduled module that sends data to its consumers through FIFOs which adds resource and energy overhead while inhibiting synthesis optimizations. In this paper we present a new algorithm for compiling image processing applications, Clockwork, that uses a combination of techniques from polyhedral analysis and synchronous dataflow (SDF) to overcome these limitations. Clockwork compiles the entire application into one flat, statically scheduled module. As a result, accelerators produced by Clockwork have fixed latency, cannot deadlock, and have no resource overhead from inter-stage FIFOs. We show that designs generated by Clockwork achieve on average a 55% reduction in LUTs, a 30% reduction in flip-flops, and a 22% reduction in BRAMs compared to a state-of-the-art stencil compiler at the same throughput, while handling a wider range of access patterns. Clockwork scales to applications with more than 100,000 LUTs. For an application with dozens of stages, Clockwork achieves energy efficiency 260x that of an 8 thread Intel CPU, 17x that of an NVIDIA K80 GPU, and 2.4x that of an NVIDIA V100 GPU.

Image processing algorithms can benefit tremendously from hardware acceleration. However, hardware accelerators for image processing algorithms look very different from the programs that image processing algorithm designers are accustomed to writing. Many image processing hardware compilers have been proposed to close this gap. Unfortunately, all of them either exclude crucial access patterns, do not scale to realistic size applications, or rely on a compilation process in which each stage of the application is an independently scheduled module that sends data to its consumers through FIFOs, which adds resource and energy overhead while inhibiting synthesis optimizations. In this work we present a new algorithm for compiling image processing applications to hardware, Clockwork, that combines insights from polyhedral analysis and synchronous dataflow to overcome these limitations. Clockwork achieves an average of 43% reduction in LUTs, 22% reduction in flip-flops, and 17% reduction in BRAMs compared to a state-of-the-art stencil compiler at the same throughput while handling a wider range of access patterns. For an image processing application with dozens of stages Clockwork achieves energy efficiency 265x that of an 8 core CPU, 17x that of an NVIDIA K80 GPU, and 2.4x that of an NVIDIA V100 GPU.

Although an agile approach is standard for software design, how to properly adapt this method to hardware is still an open question. This work addresses this question while building a system on chip (SoC) with specialized accelerators. Rather than using a traditional waterfall design flow, which starts by studying the application to be accelerated, we begin by constructing a complete flow from an application expressed in a high-level domain-specific language (DSL), in our case Halide, to a generic coarse-grained reconfigurable array (CGRA). As our under-standing of the application grows, the CGRA design evolves, and we have developed a suite of tools that tune application code, the compiler, and the CGRA to increase the efficiency of the resulting implementation. To meet our continued need to update parts of the system while maintaining the end-to-end flow, we have created DSL-based hardware generators that not only provide the Verilog needed for the implementation of the CGRA, but also create the collateral that the compiler/mapper/place and route system needs to configure its operation. This work provides a systematic approach for desiging and evolving high-performance and energy-efficient hardware-software systems for any application domain.

Designing efficient, application-specialized hardware accelerators requires assessing trade-offs between a hardware module’s performance and resource requirements. To facilitate hardware design space exploration, we describe Aetherling, a system for automatically compiling data-parallel programs into statically scheduled, streaming hardware circuits. Aetherling contributes a space- and time-aware intermediate language featuring data-parallel operators that represent parallel or sequential hardware modules, and sequence data types that encode a module’s throughput by specifying when sequence elements are produced or consumed. As a result, well-typed operator composition in the space-time language corresponds to connecting hardware modules via statically scheduled, streaming interfaces.

Symbolic model-checking is a well-established technique used in hardware design to assess, and formally verify, functional correctness. However, most modern model-checkers encode the problem into propositional satisfiability (SAT) and do not leverage any additional information beyond the input design, which is typically provided in a hardware description language such as Verilog.In this paper, we present CoSA (CoreIR Symbolic Analyzer), a model-checking tool for CoreIR designs. CoreIR is a new intermediate representation for hardware. CoSA encodes model-checking queries into first-order formulas that can be solved by Satisfiability Modulo Theories (SMT) solvers. In particular, it natively supports encodings using the theories of bitvectors and arrays. CoSA is closely integrated with CoreIR and can thus leverage CoreIR-generated metadata in addition to user-provided lemmas to assist with formal verification. CoSA supports multiple input formats and provides a broad set of analyses including equivalence checking and safety and liveness verification. CoSA is open-source and written in Python, making it easily extendable.