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1. Robust GNN-Based Representation Learning for HLS

   https://doi.org/10.1109/ICCAD57390.2023.10323853  

   Sohrabizadeh, Atefeh; Bai, Yunsheng; Sun, Yizhou; Cong, Jason (October 2023, IEEE)

   The efficient and timely optimization of microarchitecture for a target application is hindered by the long evaluation runtime of a design candidate, creating a serious burden. To tackle this problem, researchers have started using learning algorithms such as graph neural networks (GNNs) to accelerate the process by developing a surrogate of the target tool. However, challenges arise when developing such models for HLS tools due to the program's long dependency range and deeply coupled input program and transformations (i.e., pragmas). To address them, in this paper, we present HARP ( H ierarchical A ugmentation for R epresentation with P ragma optimization) with a novel hierarchical graph representation of the HLS design by introducing auxiliary nodes to include high-level hierarchical information about the design. Additionally, HARP decouples the representation of the program and its transformations and includes a neural pragma transformer (NPT) approach to facilitate a more systematic treatment of this process. Our proposed graph representation and model architecture of HARP not only enhance the performance of the model and design space exploration based on it but also improve the model's transfer learning capability, enabling easier adaptation to new environments 1 1 All materials available at https://github.com/UCLA-VAST/HARP. 

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2. Learning to Compare Hardware Designs for High-Level Synthesis

   https://doi.org/10.1145/3670474.3685940  

   Bai, Yunsheng; Sohrabizadeh, Atefeh; Ding, Zijian; Liang, Rongjian; Li, Weikai; Wang, Ding; Ren, Haoxing; Sun, Yizhou; Cong, Jason (September 2024, ACM)

   High-level synthesis (HLS) is an automated design process that transforms high-level code into optimized hardware designs, enabling rapid development of efficient hardware accelerators for various applications such as image processing, machine learning, and signal processing. To achieve optimal performance, HLS tools rely on pragmas, which are directives inserted into the source code to guide the synthesis process, and these pragmas can have various settings and values that significantly impact the resulting hardware design. State-of the-art ML-based HLS methods, such as harp, first train a deep learning model, typically based on graph neural networks (GNNs) applied to graph-based representations of the source code and its pragmas. They then perform design space exploration (DSE) to explore the pragma design space, rank candidate designs using the trained model, and return the top designs as the final designs. However, traditional DSE methods face challenges due to the highly nonlinear relationship between pragma settings and performance metrics, along with complex interactions between pragmas that affect performance in non-obvious ways. To address these challenges, we propose compareXplore, a novel approach that learns to compare hardware designs for effective HLS optimization. compareXplore introduces a hybrid loss function that combines pairwise preference learning with pointwise performance prediction, enabling the model to capture both relative preferences and absolute performance values. Moreover, we introduce a novel Node Difference Attention module that focuses on the most informative differences between designs, enhancing the model’s ability to identify critical pragmas impacting performance. compareXplore adopts a two-stage DSE approach, where a pointwise prediction model is used for the initial design pruning, followed by a pairwise comparison stage for precise performance verification. Experimental results demonstrate that compareXplore achieves significant improvements in ranking metrics and generates high quality HLS results for the selected designs, outperforming the existing state-of-the-art method. 

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3. Hierarchical Mixture of Experts: Generalizable Learning for High-Level Synthesis

   https://doi.org/10.1609/aaai.v39i17.34033  

   Li, Weikai; Wang, Ding; Ding, Zijian; Sohrabizadeh, Atefeh; Qin, Zongyue; Cong, Jason; Sun, Yizhou (April 2025, Proceedings of the AAAI Conference on Artificial Intelligence)

   High-level synthesis (HLS) is a widely used tool in designing Field Programmable Gate Array (FPGA). HLS enables FPGA design with software programming languages by compiling the source code into an FPGA circuit. The source code includes a program (called ``kernel'') and several pragmas that instruct hardware synthesis, such as parallelization, pipeline, etc. While it is relatively easy for software developers to design the program, it heavily relies on hardware knowledge to design the pragmas, posing a big challenge for software developers. Recently, different machine learning algorithms, such as GNNs, have been proposed to automate the pragma design via performance prediction. However, when applying the trained model on new kernels, the significant domain shift often leads to unsatisfactory performance. We propose a more domain-generalizable model structure: a two-level hierarchical Mixture of Experts (MoE), that can be flexibly adapted to any GNN model. Different expert networks can learn to deal with different regions in the representation space, and they can utilize similar patterns between the old kernels and new kernels. In the low-level MoE, we apply MoE on three natural granularities of a program: node, basic block, and graph. The high-level MoE learns to aggregate the three granularities for the final decision. To stably train the hierarchical MoE, we further propose a two-stage training method. Extensive experiments verify the effectiveness of the hierarchical MoE. 

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4. Automatic Hardware Pragma Insertion in High-Level Synthesis: A Non-Linear Programming Approach

   https://doi.org/10.1145/3711847  

   Pouget, Stéphane; Pouchet, Louis-Noël; Cong, Jason (March 2025, ACM Transactions on Design Automation of Electronic Systems)

   High-Level Synthesis enables the rapid prototyping of hardware accelerators, by combining a high-level description of the functional behavior of a kernel with a set of micro-architecture optimizations as inputs. Such optimizations can be described by inserting pragmas e.g., pipelining and replication of units, or even higher level transformations for HLS such as automatic data caching using the AMD/Xilinx Merlin compiler. Selecting the best combination of pragmas, even within a restricted set, remains particularly challenging and the typical state-of-practice uses design-space exploration to navigate this space. But due to the highly irregular performance distribution of pragma configurations, typical DSE approaches are either extremely time consuming, or operating on a severely restricted search space. This work proposes a framework to automatically insert HLS pragmas in regular loop-based programs, supporting pipelining, unit replication, and data caching. We develop an analytical performance and resource model as a function of the input program properties and pragmas inserted, using non-linear constraints and objectives. We prove this model provides a lower bound on the actual performance after HLS. We then encode this model as a Non-Linear Program, by making the pragma configuration unknowns of the system, which is computed optimally by solving this NLP. This approach can also be used during DSE, to quickly prune points with a (possibly partial) pragma configuration, driven by lower bounds on achievable latency. We extensively evaluate our end-to-end, fully implemented system, showing it can effectively manipulate spaces of billions of designs in seconds to minutes for the kernels evaluated. 

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5. Cross-Modality Program Representation Learning for Electronic Design Automation with High-Level Synthesis

   https://doi.org/10.1145/3670474.3685952  

   Qin, Zongyue; Bai, Yunsheng; Sohrabizadeh, Atefeh; Ding, Zijian; Hu, Ziniu; Sun, Yizhou; Cong, Jason (September 2024, ACM)

   In recent years, domain-specific accelerators (DSAs) have gained popularity for applications such as deep learning and autonomous driving. To facilitate DSA designs, programmers use high-level synthesis (HLS) to compile a high-level description written in C/C++ into a design with low-level hardware description languages that eventually synthesize DSAs on circuits. However, creating a highquality HLS design still demands significant domain knowledge, particularly in microarchitecture decisions expressed as pragmas. Thus, it is desirable to automate such decisions with the help of machine learning for predicting the quality of HLS designs, requiring a deeper understanding of the program that consists of original code and pragmas. Naturally, these programs can be considered as sequence data. In addition, these programs can be compiled and converted into a control data flow graph (CDFG). But existing works either fail to leverage both modalities or combine the two in shallow or coarse ways. We propose ProgSG, a model that allows interaction between the source code sequence modality and the graph modality in a deep and fine-grained way. To alleviate the scarcity of labeled designs, a pre-training method is proposed based on a suite of compiler’s data flow analysis tasks. Experimental results show that ProgSG reduces the RMSE of design performance predictions by up to 22%, and identifies designs with an average of 1.10× and 1.26× (up to 8.17× and 13.31×) performance improvement in design space exploration (DSE) task compared to HARP and AutoDSE, respectively. 

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