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Eric Fiselier 5de7cacf07 Make GCC in C++03 Unsupported 
Summary:
This patch make G++03 explicitly unsupported with libc++, as discussed on the mailing lists.


Below is the rational for this decision.
----------------------------------------------------------------------------------------------------

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
 		2019-06-13 00:37:25 +00:00
clang [clang-scan-deps] Include <mutex> in ClangScanDeps.cpp to ensure it 2019-06-12 21:52:36 +00:00
clang-tools-extra [clangd] Return TextEdits from ClangdServer::applyTweak 2019-06-12 12:03:24 +00:00
compiler-rt [compiler-rt] Fix name_to_handle_at.cc test on Overlay2 (for Docker) 2019-06-12 14:19:24 +00:00
debuginfo-tests Add cdb test for global constants 2019-06-06 20:23:05 +00:00
libclc travis: Add LLVM-8 build 2019-03-27 21:28:31 +00:00
libcxx Make GCC in C++03 Unsupported 2019-06-13 00:37:25 +00:00
libcxxabi [demangle] Vendor extended types shouldn't be considered substitution candidates 2019-06-10 21:02:39 +00:00
libunwind [Docs] Modernize references to macOS 2019-05-30 16:46:22 +00:00
lld [lld] Fix type server merging with PDBs without IPI stream 2019-06-12 22:33:16 +00:00
lldb [Reproducers] Simplify providers with nested Info struct (NFC) 2019-06-12 22:17:38 +00:00
llgo IR: Support parsing numeric block ids, and emit them in textual output. 2019-03-22 18:27:13 +00:00
llvm [SLP] Update propagate_ir_flags.ll test to check that we do retain the common subset, NFC. 2019-06-13 00:19:50 +00:00
openmp Added propagation of not big initial stack size of master thread to workers. 2019-06-05 16:14:47 +00:00
parallel-libs Fix typos throughout the license files that somehow I and my reviewers 2019-01-21 09:52:34 +00:00
polly [ScopBuilder] Move addInvariantLoads to ScopBuilder. NFC. 2019-06-12 22:51:56 +00:00
pstl [pstl] The optimized parallel versions of sort, stable_sort algorithms, TBB parallel backend. 2019-06-06 07:34:46 +00:00
.arcconfig Update monorepo .arcconfig with new project callsign. 2019-01-31 14:34:59 +00:00
.clang-format Add .clang-tidy and .clang-format files to the toplevel of the 2019-01-29 16:43:16 +00:00
.clang-tidy Disable tidy checks with too many hits 2019-02-01 11:20:13 +00:00
.gitignore Add a reduced copy of the llvm .gitignore 2019-04-09 00:52:49 +00:00
README.md
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README.md

The LLVM Compiler Infrastructure

This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.