Leveraging Large Language Models for Generalizing Peephole Optimizations

2026-03-19

AI Summary

Handcrafted generalization of peephole optimization rules is costly and error-prone, while existing automated approaches suffer from limited generalizability. This work proposes LPG, a novel framework that integrates large language models with formal verification to automatically synthesize correct and efficient optimization rules within a closed-loop pipeline. By leveraging semantic abstraction, symbolic constants, structural generalization, constraint relaxation, and bit-width/precision generalization, LPG achieves robust rule generalization. Evaluated on real-world LLVM cases, LPG successfully generalizes 90 out of 102 rules and substantially outperforms Hydra on an integer subset (74 vs. 35), demonstrating superior capabilities in generalization, correctness, and performance gains.

Technology Category

• Search and Optimization: Learning to Search
• Natural Language Processing: Code Generation / Program Synthesis from Natural Language
• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories

Application Category

• Economics, Online Markets and Human Computation: Cost models of using LLMs in production systems
• Semantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs
• User Modeling, Personalization and Recommendation: Large Language Models (LLM) for user modeling and recommendation

Abstract

Peephole optimizations are a core component of modern optimizing compilers. It rewrites specific instruction into semantically equivalent but more efficient forms. In practice, creating a new peephole optimization often starts from a concrete optimization instance and requires lifting it into a more general rewrite rule that matches a wider range of instruction patterns. This generalization step is critical to optimization effectiveness, but it is also difficult: producing rules that are both correct and sufficiently general typically demands substantial manual effort and domain expertise. Existing approaches such as Hydra attempt to automate this task with program synthesis, but their generalization capability is often limited by search-space explosion, under-generalization, and restricted support for diverse instruction domains. We present LPG, large language model aided peephole optimization generalization, a framework that uses large language models (LLMs) to generalize peephole optimizations. The design of LPG is motivated by the observation that LLMs are effective at semantic abstraction and exploratory reasoning, while formal analyses are necessary to ensure that generated rules are sound and profitable. Based on this observation, LPG adopts a closed-loop workflow that integrates LLM-driven symbolic constant generalization, structural generalization, constraint relaxation, and bitwidth/precision generalization with feedback from syntactic validation, semantic verification, and profitability checking. We evaluate LPG on real-world peephole optimization issues drawn from the LLVM ecosystem. Overall, LPG successfully generalizes 90 out of 102 optimizations. On the integer-focused subset that is directly comparable to Hydra, LPG generalizes 74 out of 81 optimizations, whereas Hydra generalizes 35.

Problem

• peephole optimization
• generalization
• compiler optimization
• rewrite rules
• program synthesis

Innovation

• peephole optimization
• large language models
• program generalization
• compiler optimization
• formal verification