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Process Supervision-Guided Policy Optimization for Code Generation

Paper · 2024 · Ning Dai, Zheng Wu, Renjie Zheng et al.

Summary

RL from unit-test feedback helps LLMs write better code, but the reward is sparse. A single pass/fail signal arrives only after the whole program runs, and a program that fails every test gives the model nothing to learn from. The authors (ByteDance and Oregon State University) propose Process Supervision-Guided Policy Optimization (PSGPO), which adds a Process Reward Model (PRM) that scores each generated line of code.

PRM training labels are produced automatically. A policy response is split into line-level prefixes, best-of-K completions are sampled from each prefix and executed against unit tests, and a binary search finds the point after which no completion succeeds. In RL, the PRM plays two roles at once: it supplies dense per-line rewards, and it initializes the value function. This combination worked best and raised pass rates on HumanEval, MBPP and LiveCodeBench for two base LLMs, with the clearest gains on long outputs. The work matters because it brings process supervision, previously explored mostly for math reasoning, to code generation and offers a practical recipe for using it.

Key points

  • PRM labels need no human annotation. A prefix counts as correct (+1) if any of K sampled completions passes all unit tests, and incorrect (−1) otherwise. Binary search over lines keeps the number of checks low.
  • Using the PRM both as a dense reward and as the value-model initialization gave a stronger synergy than either use alone. The authors also report better exploration and learning efficiency.
  • In the response-length analysis, PRM-trained models improved Pass@1 by about 9% over the baseline. Gains were consistent for responses longer than 100 tokens, while shorter responses saw neutral or slightly negative effects.
  • PRM data selection affects results. On LiveCodeBench with Doubao-Lite-RL, the scores were:
    • Full data: 26.9
    • Remove Hard: 27.8
    • Medium Only: 26.9
    • Revised Only: 29.8 (best)
  • Policy quality kept improving as more responses per prompt were collected for PRM data. The main limitations are:
    • noisy automatic labels;
    • high compute cost;
    • reliance on unit tests, which limits use in tasks without clear correctness checks.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Fields, topics and concepts

Cite

Cite as Ning Dai, Zheng Wu, Renjie Zheng, Ziyun Wei, Wenlei Shi, Xing Jin, Guanlin Liu, Chen Dun, Liang Huang and Lin Yan. 2024. Process Supervision-Guided Policy Optimization for Code Generation. arXiv:2410.17621.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.2410.17621 · arXiv 2410.17621

@misc{dai2024process,
  title = {{Process Supervision-Guided Policy Optimization for Code Generation}},
  author = {Ning Dai, Zheng Wu, Renjie Zheng, Ziyun Wei, Wenlei Shi, Xing Jin, Guanlin Liu, Chen Dun, Liang Huang and Lin Yan},
  year = {2024},
  doi = {10.48550/arxiv.2410.17621},
  eprint = {2410.17621},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.2410.17621}
}

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