Program Bindings Inside Code Models

Prateek Kumar Rajput, Yewei Song, Jacques Klein, Tegawendé F. Bissyandé

Code language models complete, review, and repair programs without exposing the program structure encoded in their hidden states. In this paper, we test whether the hidden states of a code model can be described and edited using the information a compiler front end computes. For each token of a Python program, standard analyzers provide its position in the abstract syntax tree, its scope, its definition-use links, and its syntactic category. We fit a decomposition that expresses every hidden state of a frozen model as a sum of one term per token, each combining the token with this structural label, and we replace the model's own states with the decomposition at every layer while it predicts the output of a small program. If the model still answers correctly, the decomposition preserves the information the model uses. We apply this test to 14 open models, seven of them trained for code, and compare against a baseline decomposition of the same size built from token positions. The static-analysis decomposition preserves the model's answers better than the positional one in 10 of the 14 models, including six of the seven code models, and deleting the definition-use links from it…