Chiseling Out Efficiency: Structured Skeleton Supervision for Efficient Code Generation

Large Language Models (LLMs) are capable of generating syntactically correct and functionally complete programs, greatly streamlining software development. However, recent studies reveal that these programs typically execute substantially slower than human-optimized counterparts. Existing approaches to bridging this efficiency gap typically involve either iteratively optimizing code after generation or fine-tuning models on corpora of efficient code. Yet, these methods expose the model to efficiency signals only by mimicking complete, optimized solutions, without explicitly encoding the structural code patterns essential for achieving high runtime performance. Addressing this gap presents two core challenges: (1) extracting and representing latent, efficiency-oriented structural patterns embedded within complex syntax and control flows, and (2) effectively learning these patterns without destabilizing the semantic training of LLMs. To tackle these challenges, we propose EffiSkel, an effi ciency skel eton-guided framework that explicitly extracts and learns efficiency skeletons—abstract, reusable structural patterns underpinning efficient code—by leveraging three complementary strategies: lexical analysis based on token-frequency saliency, syntactic analysis using similarity over Abstract Syntax Trees (ASTs), and dynamic line-level profiling of execution time. These skeletons are integrated into a multi-task learning regime that jointly optimizes code generation and skeleton prediction, introducing an explicit inductive bias toward efficiency-aware code generation. Experiments across multiple programming languages and benchmarks demonstrate that EffiSkel significantly enhances both functional correctness and efficiency, resulting on Mercury with DeepSeek-Coder (6.7B) a +11.11% (vs. EffiCoder) and +3.71% (vs. CodeDPO) higher Efficiency Ratio (ER), and a +0.36 (vs. EffiCoder) and +0.22 (vs. CodeDPO) increase in Average Speedup (AS). These results highlight the effectiveness of explicitly modeling efficiency skeletons in improving the runtime performance of code generated by LLMs.