Published
Dec 25, 2024
Updated
Dec 25, 2024

Do LLMs Write Buggy Code?

How Propense Are Large Language Models at Producing Code Smells? A Benchmarking Study
By
Alejandro Velasco|Daniel Rodriguez-Cardenas|David N. Palacio|Luftar Rahman Alif|Denys Poshyvanyk

Summary

Large language models (LLMs) are revolutionizing coding, but are they secretly introducing flaws? A new study reveals that LLMs have a surprising tendency to generate 'code smells'—subtle hints of deeper design and implementation problems. These aren't outright bugs, but they can make code harder to understand, maintain, and evolve, potentially leading to more serious issues down the line. Researchers have developed a new benchmark called CodeSmellEval, along with a dataset of over 142,000 code smells called CodeSmellData, to evaluate just how 'smelly' LLM-generated code can be. Using a metric called the Propensity Smelly Score (PSC), they analyzed two leading LLMs, CodeLlama and Mistral. The results? Both models showed a propensity for generating certain types of code smells, like overly complex conditional statements and unnecessary type checks. Interestingly, some smells were more common than others, suggesting that LLMs might have blind spots when it comes to certain coding best practices. This research has significant implications for developers relying on LLMs. While LLMs offer powerful code generation capabilities, it's crucial to be aware of their potential to introduce hidden quality issues. Future research aims to explore *why* LLMs generate these smells and develop techniques to mitigate them, paving the way for more reliable and trustworthy AI-powered coding tools.
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Question & Answers

What is the Propensity Smelly Score (PSC) and how is it used to evaluate LLM-generated code?
The Propensity Smelly Score (PSC) is a metric developed to quantify the prevalence of code smells in LLM-generated code. It works by analyzing code patterns and identifying potential design and implementation issues that could impact code maintainability and reliability. The metric was applied to evaluate CodeLlama and Mistral's outputs, specifically looking for issues like complex conditional statements and unnecessary type checks. For example, if an LLM generates a function with deeply nested if-statements or redundant type checking, it would receive a higher PSC score, indicating potentially problematic code quality. This scoring system helps developers understand the likelihood of receiving code with maintainability issues when using specific LLMs.
What are code smells and why should developers care about them?
Code smells are warning signs in software that indicate potential underlying problems in the code's design or implementation. While they're not bugs that immediately break functionality, they can make code harder to maintain, update, and understand over time. Think of them like small warning lights on a car's dashboard - they don't mean the car will break down immediately, but they suggest potential future problems. For businesses and developers, identifying and addressing code smells early can prevent technical debt, reduce maintenance costs, and make it easier for team members to collaborate on projects. Common examples include overly complex methods, duplicate code, or unnecessarily complicated conditional logic.
How is AI changing the way we write and maintain code?
AI is transforming software development by automating code generation, suggesting improvements, and helping developers work more efficiently. Large language models can now generate entire code segments, complete functions, and even debug existing code, significantly speeding up the development process. This technology makes coding more accessible to beginners while helping experienced developers focus on higher-level problem-solving. However, as highlighted by recent research, AI assistance comes with its own challenges, such as potential code quality issues. The key to successful AI-powered development is understanding both its capabilities and limitations, using it as a helpful tool rather than a complete replacement for human expertise.

PromptLayer Features

  1. Testing & Evaluation
  2. The paper's CodeSmellEval benchmark aligns with PromptLayer's testing capabilities for evaluating code quality metrics
Implementation Details
1. Create test suites with code smell detection metrics 2. Configure batch testing pipelines 3. Set up automated PSC scoring 4. Track results across model versions
Key Benefits
• Automated detection of code quality issues • Consistent evaluation across different LLM versions • Historical tracking of code smell metrics
Potential Improvements
• Add custom code smell detection rules • Integrate with popular code analysis tools • Implement real-time quality alerts
Business Value
Efficiency Gains
Reduces manual code review time by 40-60%
Cost Savings
Prevents technical debt from poor code quality
Quality Improvement
Ensures consistent code quality standards across LLM outputs
  1. Analytics Integration
  2. Tracking and analyzing code smell patterns in LLM outputs requires robust analytics capabilities
Implementation Details
1. Set up code quality metrics tracking 2. Configure performance monitoring dashboards 3. Implement pattern detection algorithms
Key Benefits
• Real-time visibility into code quality trends • Early detection of problematic patterns • Data-driven model selection
Potential Improvements
• Enhanced visualization of code smell patterns • Predictive analytics for quality issues • Integration with development workflows
Business Value
Efficiency Gains
Reduces debugging time by identifying issues early
Cost Savings
Optimizes model selection based on quality metrics
Quality Improvement
Enables continuous monitoring and improvement of code generation quality

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