Synthetic Semantic Supervision for Contrastive Code Representation Learning in Small Transformers: An Empirical Study

Kenneth Paulsen, Florian Tambon, Mike Papadakis, Shin Yoo


Abstract
General-purpose code embeddings power tools for code search, classification, and retrieval. Compact transformer encoders for code typically rely on either human-written docstrings (labor-intensive and inconsistent) or mined structural signals such as execution traces (setting-specific and costly to collect). We empirically study an alternative: contrastive pretraining of small encoders with synthetically generated natural-language descriptions emphasizing code functionality and intent, paired with code in a dual-encoder framework at training and discarded at inference. We benchmark this approach against pretraining-based baselines, generalist LLMs, and embedding-specific models on eight retrieval, classification, and generation tasks across C, C++, and Java. Synthetic semantic supervision yields statistically significant gains over pretraining baselines of the same inference-time size on five of eight tasks, with parity on two more; once fine-tuned, it matches or exceeds zero-shot models two orders of magnitude larger on classification, and it stays on par with execution-aware supervision at matched pretraining data, suggesting a scalable, effective alternative to existing code-representation paradigms.
Anthology ID:
2026.findings-emnlp.1905
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
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SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
40595–40615
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URL:
https://aclanthology.org/2026.findings-emnlp.1905/
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Bibkey:
Cite (ACL):
Kenneth Paulsen, Florian Tambon, Mike Papadakis, and Shin Yoo. 2026. Synthetic Semantic Supervision for Contrastive Code Representation Learning in Small Transformers: An Empirical Study. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 40595–40615, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Synthetic Semantic Supervision for Contrastive Code Representation Learning in Small Transformers: An Empirical Study (Paulsen et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1905.pdf