d6fae7f921
The Generic_GCC::GCCInstallationDetector class picks the GCC installation directory with the largest version number. Since the location of the libstdc++ include directories is tied to the GCC version, this can break C++ compilation if the libstdc++ headers for this particular GCC version are not available. Linux distributions tend to package the libstdc++ headers separately from GCC. This frequently leads to situations in which a newer version of GCC gets installed as a dependency of another package without installing the corresponding libstdc++ package. Clang then fails to compile C++ code because it cannot find the libstdc++ headers. Since libstdc++ headers are in fact installed on the system, the GCC installation continues to work, the user may not be aware of the details of the GCC detection, and the compiler does not recognize the situation and emit a warning, this behavior can be hard to understand - as witnessed by many related bug reports over the years. The goal of this work is to change the GCC detection to prefer GCC installations that contain libstdc++ include directories over those which do not. This should happen regardless of the input language since picking different GCC installations for a build that mixes C and C++ might lead to incompatibilities. Any change to the GCC installation detection will probably have a negative impact on some users. For instance, for a C user who relies on using the GCC installation with the largest version number, it might become necessary to use the --gcc-install-dir option to ensure that this GCC version is selected. This seems like an acceptable trade-off given that the situation for users who do not have any special demands on the particular GCC installation directory would be improved significantly. This patch does not yet change the automatic GCC installation directory choice. Instead, it does introduce a warning that informs the user about the future change if the chosen GCC installation directory differs from the one that would be chosen if the libstdc++ headers are taken into account. See also this related Discourse discussion: https://discourse.llvm.org/t/rfc-take-libstdc-into-account-during-gcc-detection/86992. This patch reapplies #145056. The test in the original PR did not specify a target in the clang RUN line and used a wrong way of piping to FileCheck.
C language Family Front-end
Welcome to Clang.
This is a compiler front-end for the C family of languages (C, C++ and Objective-C) which is built as part of the LLVM compiler infrastructure project.
Unlike many other compiler frontends, Clang is useful for a number of things beyond just compiling code: we intend for Clang to be host to a number of different source-level tools. One example of this is the Clang Static Analyzer.
If you're interested in more (including how to build Clang) it is best to read the relevant websites. Here are some pointers:
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Information on Clang: http://clang.llvm.org/
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Building and using Clang: http://clang.llvm.org/get_started.html
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Clang Static Analyzer: http://clang-analyzer.llvm.org/
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Information on the LLVM project: http://llvm.org/
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If you have questions or comments about Clang, a great place to discuss them is on the Clang forums:
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If you find a bug in Clang, please file it in the LLVM bug tracker: