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Explaining the Behavior of Neural Cost Models for Assembly Code Execution


Core Concepts
COMET, a framework for generating faithful, generalizable, and intuitive explanations of neural cost models' predictions for assembly code basic blocks.
Abstract
The content presents COMET, a novel framework for efficiently generating explanations for the predictions made by neural cost models for assembly code basic blocks. Key highlights: COMET formalizes the ideal properties of explanations (faithfulness, generalizability, and simplicity) as an optimization problem, and then develops a practical solution by relaxing the requirements. COMET decomposes the input basic block into features like instructions, data dependencies, and number of instructions. It then uses a custom perturbation algorithm to generate diverse perturbed basic blocks that preserve subsets of these features. COMET evaluates the precision and coverage of the feature subsets to identify the one that best explains the neural cost model's prediction for the input basic block. Experiments show that COMET's explanations accurately reflect the behavior of both neural and simulation-based cost models. The explanations also provide insights into the potential sources of errors in neural cost models compared to simulation-based models. COMET's explanations can help improve trust in neural cost models and guide their development towards more accurate and interpretable models.
Stats
The throughput cost of the basic block in Listing 1(a) predicted by the neural cost model Ithemal for the Haswell microarchitecture is 1.3 cycles. The canonical forms of the individual instructions in the basic block in Listing 1(a) have similar throughputs on the Haswell microarchitecture.
Quotes
"COMET aims to help our stakeholders, i.e. compiler and performance engineers, develop an intuition about and debug neural cost models in a simple yet precise way." "We anticipate this work to go a long way in developing better neural cost models and making them trustworthy."

Key Insights Distilled From

by Isha Chaudha... at arxiv.org 04-19-2024

https://arxiv.org/pdf/2302.06836.pdf
COMET: Neural Cost Model Explanation Framework

Deeper Inquiries

How can COMET's explanations be used to guide the development of more accurate and interpretable neural cost models?

COMET's explanations can provide valuable insights into the behavior of neural cost models by identifying the specific features of a basic block that are crucial for the model's predictions. By analyzing these explanations, developers can gain a deeper understanding of how the model makes its predictions and which features it prioritizes. This information can guide the refinement of the neural cost model by highlighting areas where the model may be overlooking important features or where it may be placing too much emphasis. Developers can use COMET's explanations to fine-tune the model's architecture, training data, or optimization algorithms to improve its accuracy and interpretability.

What are the potential limitations of COMET's perturbation-based approach, and how can they be addressed?

One potential limitation of COMET's perturbation-based approach is the computational complexity involved in generating explanations for a large number of basic blocks. As the size of the sample space increases, the time and resources required to perturb and evaluate each basic block can become significant. This limitation can be addressed by optimizing the perturbation algorithm to efficiently sample from the distribution of perturbed blocks. Techniques such as parallel processing, sampling strategies, and algorithmic optimizations can help reduce the computational burden and speed up the explanation generation process. Another limitation could be the reliance on a uniform distribution for perturbations, which may not always accurately represent the real-world variations in basic blocks. Addressing this limitation may involve incorporating domain-specific knowledge or heuristics into the perturbation algorithm to generate more realistic perturbations that better reflect the characteristics of the target instruction set architecture.

How can COMET's framework be extended to explain the behavior of cost models for other instruction set architectures beyond x86?

To extend COMET's framework to explain the behavior of cost models for other instruction set architectures beyond x86, several steps can be taken: Mapping Features: Identify the specific features relevant to the new instruction set architecture and map them to the existing feature set used by COMET for x86. This may involve understanding the unique characteristics and dependencies of the new architecture and aligning them with the features used in COMET. Custom Perturbation Algorithms: Develop custom perturbation algorithms tailored to the features and dependencies of the new instruction set architecture. These algorithms should be designed to generate diverse and realistic perturbations that capture the nuances of the architecture. Training and Validation: Train and validate COMET on datasets specific to the new instruction set architecture to ensure that the explanations generated are accurate and meaningful. This may involve adapting the framework to handle different types of instructions, data dependencies, and optimization techniques specific to the new architecture. Optimization for Efficiency: Optimize the framework for efficiency and scalability on the new architecture. This may include parallelizing computations, optimizing data structures, and fine-tuning the perturbation algorithms to handle the unique characteristics of the architecture. By following these steps and customizing COMET's framework to suit the requirements of the new instruction set architecture, developers can effectively explain the behavior of cost models across a wide range of architectures, enabling better understanding and optimization of these models.
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