Abstract
LLVM is a widely adopted compiler tool-chain, and its quality is critical to the projects relying on it. The bugs in LLVM may lead to an unpredictably large impact on the community. Usually, tools in LLVM need to interact with each other to finish a particular task. This working style brings up a specific type of bugs that involve multiple tools, namely, tool-chain bugs, which complicates the bug detection and debugging. Though there exist prior works about LLVM bugs, none of them has investigated this particular type of bugs in-depth. Thus, in this paper, we conduct an empirical study of the LLVM tool-chain bugs, aiming to provide the first comprehensive understanding of these bugs. Overall, we find 1723 tool-chain bugs. We reveal frequently occurred tool combinations, six typical interaction reasons, as well as four commonly seen failure symptoms. Through the linkages between these bugs and their fixing commits, we identify six common root causes, and summarize debugging manners. Based on the above findings, we highlight three insights into testing and debugging these bugs.