The Policy-gradient Placement and Generative Routing Neural Networks for Chip Design
Ruoyu ChengXianglong LyuYang LiJunjie YeJianye HaoJunchi Yan
As modern microchips grow increasingly complex and dense, automated physical design faces major bottlenecks. Arranging circuit components (placement) and wiring their connections (routing) are critical steps to prevent congestion and minimize total wirelength. However, traditional heuristic software tools and emerging machine learning methods struggle with real-world complexities. Specifically, existing learning-based placers oversimplify varied component dimensions, causing severe overlaps, while learning-based routers connect points sequentially, leading to high computational costs and scalability issues.
The article develops and evaluates a fully learnable, end-to-end artificial intelligence pipeline—termed PRNet—for joint component placement and routing. The objective is to demonstrate that a pure neural framework can handle mixed-size components, dynamically learn the order in which connections are routed, and generate global routes in one shot without relying on traditional heuristic solvers.
To achieve this, the authors designed a reinforcement learning placement model that incorporates actual component dimensions and fixed initial layouts. They combined this with an image-based conditional generative network featuring an input-adapting architecture, an enhanced loss function, and dual evaluators targeting path connectivity and visual realism. The framework also uses an adaptive reinforcement learning agent to dynamically determine routing sequence. The system was validated against standard industry benchmarks, including ISPD-2005 for placement and ISPD-98 and ISPD-07 for routing, using hundreds of thousands of net instances on high-performance graphics processing units.
The evaluation produced four key findings. First, on mixed-size placement benchmarks, the model reduced component overlap area roughly fourfold (about 75%) compared to the leading learning baseline DeepPlace, while maintaining nearly identical wirelengths (within 1.3%). Second, the one-shot generative routing model achieved roughly double the correctness rate and up to a 14.7% reduction in wirelength over prior generative routers. Third, dynamically learning the net routing order substantially reduced routing congestion across full circuit benchmarks compared to static heuristics. Finally, while the sequential routing model achieved zero overflow on standard test circuits, running nets concurrently accelerated throughput by roughly 3.4 to 8 times at the cost of modest increases in wirelength and overflow.
These findings demonstrate that replacing rule-based physical design tools with an integrated, pure deep learning pipeline is feasible and effective. Drastically reducing placement overlaps eliminates costly post-processing fixes, while dynamic routing ordering lowers congestion and improves routability. However, because the sequential neural router is computationally slower than highly tuned, traditional rule-based tools, deploying such models requires balancing execution speed against optimization quality.
Organizations evaluating this approach should consider a hybrid deployment: using concurrent batching when rapid design iterations are required, and sequential execution for final, high-precision layout optimization. Before moving to production environments, development teams should pilot unsupervised or semi-supervised training pipelines to remove reliance on traditional tools for training data, and extend the model from global routing to detailed routing constraints.
The findings are supported by consistent results across recognized public benchmarks, though confidence should be weighed against notable boundaries. The neural router's performance ceiling is currently tied to the quality of the classical router used to generate its training labels, and runtime remains higher than conventional heuristic tools. Continued work on model compression and broader industrial test cases will be essential to establish fully autonomous, production-grade chip design flows.
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