Is Your Code Generated by ChatGPT Really Correct? Rigorous Evaluation of Large Language Models for Code Generation

Abstract: Program synthesis has been long studied with recent approaches focused on directly using the power of Large Language Models (LLMs) to generate code according to user intent written in natural language. Code evaluation datasets, containing curated synthesis problems with input/output test-cases, are used to measure the performance of various LLMs on code synthesis. However, test-cases in these datasets can be limited in both quantity and quality for fully assessing the functional correctness of the generated code. Such limitation in the existing benchmarks begs the following question: In the era of LLMs, is the code generated really correct? To answer this, we propose EvalPlus -- a code synthesis benchmarking framework to rigorously evaluate the functional correctness of LLM-synthesized code. In short, EvalPlus takes in the base evaluation dataset and uses an automatic input generation step to produce and diversify large amounts of new test inputs using both LLM-based and mutation-based input generators to further validate the synthesized code. We extend the popular HUMANEVAL benchmark and build HUMANEVAL+ with 81x additionally generated tests. Our extensive evaluation across 14 popular LLMs demonstrates that HUMANEVAL+ is able to catch significant amounts of previously undetected wrong code synthesized by LLMs, reducing the pass@k by 15.1% on average! Moreover, we even found several incorrect ground-truth implementations in HUMANEVAL. Our work not only indicates that prior popular code synthesis evaluation results do not accurately reflect the true performance of LLMs for code synthesis but also opens up a new direction to improve programming benchmarks through automated test input generation.