Importance Guided Data Augmentation for Neural-Based Code Understanding

Pre-trained code models lead the era of code intelligence. Many models have been designed with impressive performance recently. However, one important problem, data augmentation for code data that automatically helps developers prepare training data lacks study in the field of code learning. In this paper, we introduce a general data augmentation framework, GenCode, to enhance the training of code understanding models. GenCode follows a generation-and-selection paradigm to prepare useful training codes. Specifically, it uses code transformation techniques to generate new code candidates first and then selects important ones as the training data by importance metrics. To evaluate the effectiveness of GenCode with a general importance metric -- loss value, we conduct experiments on four code understanding tasks (e.g., code clone detection) and three pre-trained code models (e.g., CodeT5). Compared to the state-of-the-art (SOTA) code augmentation method, MixCode, GenCode produces code models with 2.92% higher accuracy and 4.90% robustness on average.

Hazards in Deep Learning Testing: Prevalence, Impact and Recommendations

Much research on Machine Learning testing relies on empirical studies that evaluate and show their potential. However, in this context empirical results are sensitive to a number of parameters that can adversely impact the results of the experiments and potentially lead to wrong conclusions (Type I errors, i.e., incorrectly rejecting the Null Hypothesis). To this end, we survey the related literature and identify 10 commonly adopted empirical evaluation hazards that may significantly impact experimental results. We then perform a sensitivity analysis on 30 influential studies that were published in top-tier SE venues, against our hazard set and demonstrate their criticality. Our findings indicate that all 10 hazards we identify have the potential to invalidate experimental findings, such as those made by the related literature, and should be handled properly. Going a step further, we propose a point set of 10 good empirical practices that has the potential to mitigate the impact of the hazards. We believe our work forms the first step towards raising awareness of the common pitfalls and good practices within the software engineering community and hopefully contribute towards setting particular expectations for empirical research in the field of deep learning testing.

Evaluating the Robustness of Test Selection Methods for Deep Neural Networks

Testing deep learning-based systems is crucial but challenging due to the required time and labor for labeling collected raw data. To alleviate the labeling effort, multiple test selection methods have been proposed where only a subset of test data needs to be labeled while satisfying testing requirements. However, we observe that such methods with reported promising results are only evaluated under simple scenarios, e.g., testing on original test data. This brings a question to us: are they always reliable? In this paper, we explore when and to what extent test selection methods fail for testing. Specifically, first, we identify potential pitfalls of 11 selection methods from top-tier venues based on their construction. Second, we conduct a study on five datasets with two model architectures per dataset to empirically confirm the existence of these pitfalls. Furthermore, we demonstrate how pitfalls can break the reliability of these methods. Concretely, methods for fault detection suffer from test data that are: 1) correctly classified but uncertain, or 2) misclassified but confident. Remarkably, the test relative coverage achieved by such methods drops by up to 86.85%. On the other hand, methods for performance estimation are sensitive to the choice of intermediate-layer output. The effectiveness of such methods can be even worse than random selection when using an inappropriate layer.

Boosting Source Code Learning with Data Augmentation: An Empirical Study

The next era of program understanding is being propelled by the use of machine learning to solve software problems. Recent studies have shown surprising results of source code learning, which applies deep neural networks (DNNs) to various critical software tasks, e.g., bug detection and clone detection. This success can be greatly attributed to the utilization of massive high-quality training data, and in practice, data augmentation, which is a technique used to produce additional training data, has been widely adopted in various domains, such as computer vision. However, in source code learning, data augmentation has not been extensively studied, and existing practice is limited to simple syntax-preserved methods, such as code refactoring. Essentially, source code is often represented in two ways, namely, sequentially as text data and structurally as graph data, when it is used as training data in source code learning. Inspired by these analogy relations, we take an early step to investigate whether data augmentation methods that are originally used for text and graphs are effective in improving the training quality of source code learning. To that end, we first collect and categorize data augmentation methods in the literature. Second, we conduct a comprehensive empirical study on four critical tasks and 11 DNN architectures to explore the effectiveness of 12 data augmentation methods (including code refactoring and 11 other methods for text and graph data). Our results identify the data augmentation methods that can produce more accurate and robust models for source code learning, including those based on mixup (e.g., SenMixup for texts and Manifold-Mixup for graphs), and those that slightly break the syntax of source code (e.g., random swap and random deletion for texts).

GAT: Guided Adversarial Training with Pareto-optimal Auxiliary Tasks

While leveraging additional training data is well established to improve adversarial robustness, it incurs the unavoidable cost of data collection and the heavy computation to train models. To mitigate the costs, we propose \textit{Guided Adversarial Training } (GAT), a novel adversarial training technique that exploits auxiliary tasks under a limited set of training data. Our approach extends single-task models into multi-task models during the min-max optimization of adversarial training, and drives the loss optimization with a regularization of the gradient curvature across multiple tasks. GAT leverages two types of auxiliary tasks: self-supervised tasks, where the labels are generated automatically, and domain-knowledge tasks, where human experts provide additional labels. Experimentally, under limited data, GAT increases the robust accuracy on CIFAR-10 up to four times (from 11% to 42% robust accuracy) and the robust AUC of CheXpert medical imaging dataset from 50\% to 83\%. On the full CIFAR-10 dataset, GAT outperforms eight state-of-the-art adversarial training strategies. Our large study across five datasets and six tasks demonstrates that task augmentation is an efficient alternative to data augmentation, and can be key to achieving both clean and robust performances.

Enhancing Code Classification by Mixup-Based Data Augmentation

Recently, deep neural networks (DNNs) have been widely applied in programming language understanding. Generally, training a DNN model with competitive performance requires massive and high-quality labeled training data. However, collecting and labeling such data is time-consuming and labor-intensive. To tackle this issue, data augmentation has been a popular solution, which delicately increases the training data size, e.g., adversarial example generation. However, few works focus on employing it for programming language-related tasks. In this paper, we propose a Mixup-based data augmentation approach, MixCode, to enhance the source code classification task. First, we utilize multiple code refactoring methods to generate label-consistent code data. Second, the Mixup technique is employed to mix the original code and transformed code to form the new training data to train the model. We evaluate MixCode on two programming languages (JAVA and Python), two code tasks (problem classification and bug detection), four datasets (JAVA250, Python800, CodRep1, and Refactory), and 5 model architectures. Experimental results demonstrate that MixCode outperforms the standard data augmentation baseline by up to 6.24\% accuracy improvement and 26.06\% robustness improvement.

Enhancing Mixup-Based Graph Learning for Language Processing via Hybrid Pooling

Graph neural networks (GNNs) have recently been popular in natural language and programming language processing, particularly in text and source code classification. Graph pooling which processes node representation into the entire graph representation, which can be used for multiple downstream tasks, e.g., graph classification, is a crucial component of GNNs. Recently, to enhance graph learning, Manifold Mixup, a data augmentation strategy that mixes the graph data vector after the pooling layer, has been introduced. However, since there are a series of graph pooling methods, how they affect the effectiveness of such a Mixup approach is unclear. In this paper, we take the first step to explore the influence of graph pooling methods on the effectiveness of the Mixup-based data augmentation approach. Specifically, 9 types of hybrid pooling methods are considered in the study, e.g., $\mathcal{M}_{sum}(\mathcal{P}_{att},\mathcal{P}_{max})$. The experimental results on both natural language datasets (Gossipcop, Politifact) and programming language datasets (Java250, Python800) demonstrate that hybrid pooling methods are more suitable for Mixup than the standard max pooling and the state-of-the-art graph multiset transformer (GMT) pooling, in terms of metric accuracy and robustness.

LGV: Boosting Adversarial Example Transferability from Large Geometric Vicinity

We propose transferability from Large Geometric Vicinity (LGV), a new technique to increase the transferability of black-box adversarial attacks. LGV starts from a pretrained surrogate model and collects multiple weight sets from a few additional training epochs with a constant and high learning rate. LGV exploits two geometric properties that we relate to transferability. First, models that belong to a wider weight optimum are better surrogates. Second, we identify a subspace able to generate an effective surrogate ensemble among this wider optimum. Through extensive experiments, we show that LGV alone outperforms all (combinations of) four established test-time transformations by 1.8 to 59.9 percentage points. Our findings shed new light on the importance of the geometry of the weight space to explain the transferability of adversarial examples.

Efficient Testing of Deep Neural Networks via Decision Boundary Analysis

Deep learning plays a more and more important role in our daily life due to its competitive performance in multiple industrial application domains. As the core of DL-enabled systems, deep neural networks automatically learn knowledge from carefully collected and organized training data to gain the ability to predict the label of unseen data. Similar to the traditional software systems that need to be comprehensively tested, DNNs also need to be carefully evaluated to make sure the quality of the trained model meets the demand. In practice, the de facto standard to assess the quality of DNNs in industry is to check their performance (accuracy) on a collected set of labeled test data. However, preparing such labeled data is often not easy partly because of the huge labeling effort, i.e., data labeling is labor-intensive, especially with the massive new incoming unlabeled data every day. Recent studies show that test selection for DNN is a promising direction that tackles this issue by selecting minimal representative data to label and using these data to assess the model. However, it still requires human effort and cannot be automatic. In this paper, we propose a novel technique, named Aries, that can estimate the performance of DNNs on new unlabeled data using only the information obtained from the original test data. The key insight behind our technique is that the model should have similar prediction accuracy on the data which have similar distances to the decision boundary. We performed a large-scale evaluation of our technique on 13 types of data transformation methods. The results demonstrate the usefulness of our technique that the estimated accuracy by Aries is only 0.03% -- 2.60% (on average 0.61%) off the true accuracy. Besides, Aries also outperforms the state-of-the-art selection-labeling-based methods in most (96 out of 128) cases.

CodeS: A Distribution Shift Benchmark Dataset for Source Code Learning

Over the past few years, deep learning (DL) has been continuously expanding its applications and becoming a driving force for large-scale source code analysis in the big code era. Distribution shift, where the test set follows a different distribution from the training set, has been a longstanding challenge for the reliable deployment of DL models due to the unexpected accuracy degradation. Although recent progress on distribution shift benchmarking has been made in domains such as computer vision and natural language process. Limited progress has been made on distribution shift analysis and benchmarking for source code tasks, on which there comes a strong demand due to both its volume and its important role in supporting the foundations of almost all industrial sectors. To fill this gap, this paper initiates to propose CodeS, a distribution shift benchmark dataset, for source code learning. Specifically, CodeS supports 2 programming languages (i.e., Java and Python) and 5 types of code distribution shifts (i.e., task, programmer, time-stamp, token, and CST). To the best of our knowledge, we are the first to define the code representation-based distribution shifts. In the experiments, we first evaluate the effectiveness of existing out-of-distribution detectors and the reasonability of the distribution shift definitions and then measure the model generalization of popular code learning models (e.g., CodeBERT) on classification task. The results demonstrate that 1) only softmax score-based OOD detectors perform well on CodeS, 2) distribution shift causes the accuracy degradation in all code classification models, 3) representation-based distribution shifts have a higher impact on the model than others, and 4) pre-trained models are more resistant to distribution shifts. We make CodeS publicly available, enabling follow-up research on the quality assessment of code learning models.