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5de7cacf07
Summary:
This patch make G++03 explicitly unsupported with libc++, as discussed on the mailing lists.
Below is the rational for this decision.
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libc++ claims to support GCC with C++03 ("G++03"), and this is a problem for our users.
Our C++03 users are all using Clang. They must be. Less than 9% of the C++03 tests pass with GCC [1][2]. No non-trivial C++ program could work.
Attempting to support G++03 impacts our QoI considerably. Unlike Clang, G++03 offers almost no C++11 extensions. If we could remove all the fallbacks for G++03, it would mean libc++ could::
* Improve Correctness:
Every `#ifdef _LIBCPP_HAS_NO_<C++11-feature>` is a bug manifest. It exists to admit for deviant semantics.
* Achieve ABI stability between C++03 and C++11
Differences between our C++03 and C++Rest branches contain ABI bugs. For example `std::nullptr_t` and `std::function::operator()(...)` are currently incompatible between C++11 and C++03, but could be fixed.
* Decrease Compile Times and Memory Usage:
Writing efficient SFINAE requires C++11. Using alias templates, libc++ could reduce the number of instantiations it produces substantially.
* Decrease Binary Size
Similar to the last point, G++03 forces metaprogramming techniques that emit more debug information [3] [4]. Compared to libstdc++, debug information size increases of +10% are not uncommon.
Reviewers: ldionne, mclow.lists, EricWF
Reviewed By: ldionne, EricWF
Subscribers: zoecarver, aprantl, dexonsmith, arphaman, libcxx-commits, #libc
Differential Revision: https://reviews.llvm.org/D63154
llvm-svn: 363219
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| .. | ||
| DesignDocs | ||
| BuildingLibcxx.rst | ||
| CMakeLists.txt | ||
| conf.py | ||
| FeatureTestMacroTable.rst | ||
| index.rst | ||
| Makefile.sphinx | ||
| README.txt | ||
| ReleaseNotes.rst | ||
| TestingLibcxx.rst | ||
| UsingLibcxx.rst | ||
libc++ Documentation ==================== The libc++ documentation is written using the Sphinx documentation generator. It is currently tested with Sphinx 1.1.3. To build the documents into html configure libc++ with the following cmake options: * -DLLVM_ENABLE_SPHINX=ON * -DLIBCXX_INCLUDE_DOCS=ON After configuring libc++ with these options the make rule `docs-libcxx-html` should be available.