Existing routability-driven global placers typically employed an iterative routability optimization process and performed cell inflation based only on lookahead congestion maps during each run. However, this incremental application of congestion estimation and mitigation resulted in placement solutions that deviate from optimal wirelength, thus compromising the optimization objective of balancing wirelength minimization and routability optimization. To simultaneously improve routability and reduce wirelength, this paper proposes a novel routability–wirelength co-guided cell inflation approach for global placement optimization. It employs a multi-task learning-based feature selection method, MTL-FS, to identify the optimal feature subset and train the corresponding routability–wirelength co-learning model, RWNet. During the iterative optimization process, both routability and wirelength are predicted using RWNet, and their correlation is interpreted by DeepSHAP to produce three impact maps. Subsequently, routability–wirelength co-guided cell inflation (RWCI) is performed based on an adjusted congestion map, which is derived from the predicted congestion map and the three impact maps. The experimental results on ISPD2011 and DAC2012 benchmark designs demonstrate that, compared to DERAMPlace and RoutePlacer (which represent non-machine learning-based and machine learning-based routability-driven placers, respectively), the proposed approach achieves both better optimization quality, specifically improved routability and reduced wirelength, and a decreased time cost. Moreover, the extension experiment shows our method consistently outperforms DREAMPlace (even when it uses 2D feature maps as proxies) in effectiveness while maintaining comparable efficiency. The Generalization experiment further confirms this superiority and comparable runtime, particularly in highly congested scenarios.
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