Small and focused commits are highly valued in modern software development. However, developers sometimes submit a commit with more than one concern, represented by several lines of code changes for a specific purpose, e.g., adding new features or fixing bugs. Such composite commits confuse developers during code reviews as well as other software activities, resulting in various issues. Existing studies predominantly leverage code structure to untangle composite commits, but without considering code semantics that have been demonstrated to be important in many related studies. In this article, we propose UNTCC, a new approach that uses structural and semantic information forUNTanglingCompositeCommits. To achieve structural information, we propose the code change graph, a fine-grained, text-attributed graph representation of a commit, incorporating before-change and after-change code dependencies; and UNTCC employs the graph autoencoder to learn its structural representation. To achieve semantic information, UNTCC leverages a large language model (Llama-3.2-3B) to learn joint embeddings of the raw commit and its aligned graph representation, which guide the division of different concerns within a composite commit. The experimental evaluation using 27,853 composite commits from 9 C# and 10 Java projects shows that in terms of Accuracya/Accuracyc, UNTCC achieves 94%/74% in C# and 77%/54% in Java, outperforming state-of-the-art approaches by 2%—623%/32%—573% in C# and 22%—285%/35%—286% in Java. The results indicate that UNTCC can effectively untangle composite commits.

Continuous Integration (CI) enables developers to detect defects early and thus reduce lead time. However, the high frequency and long duration of executing CI have a detrimental effect on this practice. Existing studies have focused on using CI outcome predictors to reduce frequency. Since there is no reported project using predictive CI, it is difficult to evaluate its economic impact. This research aims to investigate predictive CI from a process perspective, including why and when to adopt predictors, what predictors to be used, and how to practice predictive CI in real projects. We innovatively employ Software Process Simulation to simulate a predictive CI process with a Discrete-Event Simulation (DES) model and conduct simulation-based experiments. We develop the Rollback-based Identification of Defective Commits (RIDEC) method to account for the negative effects of false predictions in simulations. Experimental results show that: 1) using predictive CI generally improves the effectiveness of CI, reducing time costs by up to 36.8% and the average waiting time before executing CI by 90.5%; 2) the time-saving varies across projects, with higher commit frequency projects benefiting more; and 3) predictor performance does not strongly correlate with time savings, but the precision of both failed and passed predictions should be paid more attention. Simulation-based evaluation helps identify overlooked aspects in existing research. Predictive CI saves time and resources, but improved prediction performance has limited cost-saving benefits. The primary value of predictive CI lies in providing accurate and quick feedback to developers, aligning with the goal of CI.