Rewriting Pre-Training Data Boosts LLM Performance in Math and Code

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Main Authors: Fujii, Kazuki, Tajima, Yukito, Mizuki, Sakae, Kawamura, Masaki, Shimada, Hinari, Shiotani, Taihei, Saito, Koshiro, Oi, Masanari, Nakamura, Taishi, Okamoto, Takumi, Ishida, Shigeki, Hattori, Kakeru, Ma, Youmi, Takamura, Hiroya, Yokota, Rio, Sakuma, Jun, Okazaki, Naoaki
Format: Preprint
Published: 2025
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author Fujii, Kazuki
Tajima, Yukito
Mizuki, Sakae
Kawamura, Masaki
Shimada, Hinari
Shiotani, Taihei
Saito, Koshiro
Oi, Masanari
Nakamura, Taishi
Okamoto, Takumi
Ishida, Shigeki
Hattori, Kakeru
Ma, Youmi
Takamura, Hiroya
Yokota, Rio
Sakuma, Jun
Okazaki, Naoaki
author_facet Fujii, Kazuki
Tajima, Yukito
Mizuki, Sakae
Kawamura, Masaki
Shimada, Hinari
Shiotani, Taihei
Saito, Koshiro
Oi, Masanari
Nakamura, Taishi
Okamoto, Takumi
Ishida, Shigeki
Hattori, Kakeru
Ma, Youmi
Takamura, Hiroya
Yokota, Rio
Sakuma, Jun
Okazaki, Naoaki
contents The performance of large language models (LLMs) in program synthesis and mathematical reasoning is fundamentally limited by the quality of their pre-training corpora. We introduce two openly licensed pre-training datasets, released under the Llama 3.3 Community License, that significantly enhance LLM performance by systematically rewriting public data. SwallowCode ($\approx$16.1 billion tokens) refines Python snippets from The-Stack-v2 through a novel four-stage pipeline: syntax validation, pylint-based style filtering, and a two-stage LLM rewriting process that enforces style conformity and transforms snippets into self-contained, algorithmically efficient examples. Unlike prior methods that rely on exclusionary filtering or limited transformations, our transform-and-retain approach refines low-quality code, maximizing data utility. SwallowMath ($\approx$2.3 billion tokens) enhances Finemath-4+ by removing boilerplate, restoring context, and reformatting solutions into concise, step-by-step explanations. Within a fixed 50 billion token training budget, continual pre-training of Llama-3.1-8B with SwallowCode boosts pass@1 by +17.0 on HumanEval and +16.1 on HumanEval+ compared to Stack-Edu, surpassing the baseline model's code generation capabilities. Similarly, substituting SwallowMath yields +12.4 accuracy on GSM8K and +7.6 on MATH. Ablation studies confirm that each pipeline stage contributes incrementally, with rewriting yielding the largest gains. By releasing datasets, prompts, checkpoints, and pipeline code, we ensure reproducibility and provide a transferable transform-and-retain methodology that can be adapted to other base models and LLM rewriting setups.
format Preprint
id arxiv_https___arxiv_org_abs_2505_02881
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Rewriting Pre-Training Data Boosts LLM Performance in Math and Code
Fujii, Kazuki
Tajima, Yukito
Mizuki, Sakae
Kawamura, Masaki
Shimada, Hinari
Shiotani, Taihei
Saito, Koshiro
Oi, Masanari
Nakamura, Taishi
Okamoto, Takumi
Ishida, Shigeki
Hattori, Kakeru
Ma, Youmi
Takamura, Hiroya
Yokota, Rio
Sakuma, Jun
Okazaki, Naoaki
Machine Learning
Artificial Intelligence
The performance of large language models (LLMs) in program synthesis and mathematical reasoning is fundamentally limited by the quality of their pre-training corpora. We introduce two openly licensed pre-training datasets, released under the Llama 3.3 Community License, that significantly enhance LLM performance by systematically rewriting public data. SwallowCode ($\approx$16.1 billion tokens) refines Python snippets from The-Stack-v2 through a novel four-stage pipeline: syntax validation, pylint-based style filtering, and a two-stage LLM rewriting process that enforces style conformity and transforms snippets into self-contained, algorithmically efficient examples. Unlike prior methods that rely on exclusionary filtering or limited transformations, our transform-and-retain approach refines low-quality code, maximizing data utility. SwallowMath ($\approx$2.3 billion tokens) enhances Finemath-4+ by removing boilerplate, restoring context, and reformatting solutions into concise, step-by-step explanations. Within a fixed 50 billion token training budget, continual pre-training of Llama-3.1-8B with SwallowCode boosts pass@1 by +17.0 on HumanEval and +16.1 on HumanEval+ compared to Stack-Edu, surpassing the baseline model's code generation capabilities. Similarly, substituting SwallowMath yields +12.4 accuracy on GSM8K and +7.6 on MATH. Ablation studies confirm that each pipeline stage contributes incrementally, with rewriting yielding the largest gains. By releasing datasets, prompts, checkpoints, and pipeline code, we ensure reproducibility and provide a transferable transform-and-retain methodology that can be adapted to other base models and LLM rewriting setups.
title Rewriting Pre-Training Data Boosts LLM Performance in Math and Code
topic Machine Learning
Artificial Intelligence
url https://arxiv.org/abs/2505.02881