Enriching Compiler Testing with Real Program from Bug Report

Differential testing is widely used to detect bugs in compilers. Its basic idea is to compile test programs with different compilers, and compare their compilation results to detect bugs. In this research line, researchers have proposed various approaches to generate test programs. The state-of-the-art approaches can be roughly divided into random-based and mutation-based approaches: random-based approaches generate random programs and mutation-based approaches mutate programs to generate more test programs. Both lines of approaches mainly generate random code, but it is more beneficial to use real programs, since it is easier to learn the impacts of compiler bugs and it becomes reasonable to use both valid and invalid code. However, most real programs from code repositories are ineffective to trigger compiler bugs, partially because they are compiled before they are submitted. In this experience paper, we apply two techniques such as differential testing and code snippet extraction to the specific research domain of compiler testing. Based on our observations on the practice of testing compilers, we identify bug reports of compilers as a new source for compiler testing. To illustrate the benefits of the new source, we implement a tool, called LeRe, that extracts test programs from bug reports and uses differential testing to detect compiler bugs with extracted programs. After we enriched the test programs, we have found 156 unique bugs in the latest versions of gcc and clang. Among them, 103 bugs are confirmed as valid, and 9 bugs are already fixed. Our found bugs contain 59 accept-invalid bugs and 33 reject-valid bugs. In these bugs, compilers wrongly accept invalid programs or reject valid programs. The new source enables us detecting accept-invalid and reject-valid bugs that were usually missed by the prior approaches. The prior approaches seldom report the two types of bugs. Besides our found bugs, we also present our analysis on our invalid bug reports. The results are useful for programmers, when they are switching from one compiler to another, and can provide insights, when researchers apply differential testing to detect bugs in more types of software.