Index: cmake/modules/CheckCompilerVersion.cmake =================================================================== --- cmake/modules/CheckCompilerVersion.cmake +++ cmake/modules/CheckCompilerVersion.cmake @@ -1,6 +1,6 @@ # Check if the host compiler is new enough. # These versions are updated based on the following policy: -# llvm.org/docs/GettingStarted.html#host-c-toolchain-both-compiler-and-standard-library +# llvm.org/docs/DeveloperPolicy.html#toolchain include(CheckCXXSourceCompiles) Index: docs/DeveloperPolicy.rst =================================================================== --- docs/DeveloperPolicy.rst +++ docs/DeveloperPolicy.rst @@ -22,7 +22,7 @@ #. Make life as simple and easy for contributors as possible. -#. Keep the tip of tree as stable as possible. +#. Keep the top of tree as stable as possible. #. Establish awareness of the project's :ref:`copyright, license, and patent policies ` with contributors to the project. @@ -638,6 +638,47 @@ status, but also markers to define bit-rot, and will be used to clean up the tree from unmaintained targets. +.. _toolchain: + +Updating Toolchain Requirements +------------------------------- + +We intend to require newer toolchains as time goes by. This means LLVM's +codebase can use newer versions of C++ as they get standardized. Requiring newer +toolchains to build LLVM can be painful for those building LLVM, it will +therefore only be done through the following process: + + * Generally, try to support LLVM and GCC versions from the last 3 years at a + minimum. This time-based guideline is not strict: we may support much older + compilers, or decide to support fewer versions. + + * An RFC is sent to the `llvm-dev mailing list `_ + + - Detail upsides of the version increase (e.g. which newer C++ language or + library features LLVM should use; avoid miscompiles in particular compiler + versions, etc). + - Detail downsides on important platforms (e.g. Ubuntu LTS status). + + * Once the RFC reaches consensus, update the CMake toolchain version checks as + well as the :doc:`getting started` guide. We want to + soft-error when developers compile LLVM. We say "soft-error" because the + error can be turned into a warning using a CMake flag. This is an important + step: LLVM still doesn't have code which requires the new toolchains, but it + soon will. If you compile LLVM but don't read the mailing list, we should + tell you! + + * Ensure that at least one LLVM release has had this soft-error. Not all + developers compile LLVM tip-of-tree. These release-bound developers should + also be told about upcoming changes. + + * Turn the soft-error into a hard-error after said LLVM release has branched. + + * Update the :doc:`coding standards` to allow the new + features we've explicitly approved in the RFC. + + * Start using the new features in LLVM's codebase. + + .. _copyright-license-patents: Copyright, License, and Patents Index: docs/GettingStarted.rst =================================================================== --- docs/GettingStarted.rst +++ docs/GettingStarted.rst @@ -220,15 +220,16 @@ ------------------------------------------------------ LLVM is very demanding of the host C++ compiler, and as such tends to expose -bugs in the compiler. We are also planning to follow improvements and -developments in the C++ language and library reasonably closely. As such, we -require a modern host C++ toolchain, both compiler and standard library, in -order to build LLVM. +bugs in the compiler. We also attempt to follow improvements and developments in +the C++ language and library reasonably closely. As such, we require a modern +host C++ toolchain, both compiler and standard library, in order to build LLVM. -For the most popular host toolchains we check for specific minimum versions in -our build systems: +LLVM is written using the subset of C++ documented in :doc:`coding +standards`. To enforce this language version, we check the most +popular host toolchains for specific minimum versions in our build systems: * Clang 3.1 +* Apple Clang 3.1 * GCC 4.8 * Visual Studio 2015 (Update 3) @@ -336,7 +337,7 @@ from the loader similar to ``libstdc++.so.6: version `GLIBCXX_3.4.20' not found``. This means you need to tweak the -rpath linker flag. -When you build Clang, you will need to give *it* access to modern C++11 +When you build Clang, you will need to give *it* access to modern C++ standard library in order to use it as your new host in part of a bootstrap. There are two easy ways to do this, either build (and install) libc++ along with Clang and then use it with the ``-stdlib=libc++`` compile and link flag,