UniPar: A Unified LLM-Based Framework for Parallel and Accelerated Code Translation in HPC

Translating programs between various parallel programming languages is an important problem in the high-performance computing (HPC) community, with implications for industry and academia. Existing tools for this problem are either too narrow in scope (translate between specific languages) and/or outdated (requiring maintenance). Recent explosive growth in the popularity of large language models (LLMs) and their ability to generate and translate code offers a potential alternative approach. Toward that end, we first need to systematically evaluate the ability of LLMs to translate between parallel languages.In this work, we introduce UniPar, a systematic evaluation framework for LLM-based parallel code translation. Specifically, in this work, we target translations between serial code, CUDA, and OpenMP. Our goal is to assess how well current instruction-tuned LLMs - specifically GPT-4o-mini and LLaMA-3.3-70B-Instruct - can be used out of the box or enhanced through known strategies. We evaluated four major usage modes: hyperparameter optimization for decoding, zero- and few-shot prompting, supervised fine-tuning, and iterative feedback through compiler-based repair. As a part of the evaluation, we construct a new dataset called ParaTrans, covering both serial-to-parallel translation and cross-paradigm transformations.Our findings reveal that while off-the-shelf models struggle under the default settings (e.g., GPT-4o-mini achieves only 46% compilation and 15% functional correctness), our UniPar methodology - combining fine-tuning, hyperparameter tuning, and compiler-guided repair - improves performance by up to 2X (69% compilation and 33% correctness). We believe that our findings will provide useful insights for researchers to further improve LLMs for the parallel language translation problem.UniPar source code and ParaTrans dataset are available at our GitHub repository.