Create new library 'libc++experimental.a' for packaging TS symbols.

Summary:
Out-of-line symbols for <experimental/...> headers are not ABI or API stable and cannot live in the 'libc++.dylib'. Currently they have nowhere to live. I would like to add a new library target `libc++experimental.a` to fix this. 

Previously I had suggested different libraries for different TS's (`libc++filesystem.a`, 'libc++LFTS.a`, ect). I no longer think this is the right approach.
Instead `c++experimental` will hold *all* TS implementations as a single monolithic library. I see two main benefits to this:

1. Users only have to know about and manually link one library.
2. It makes it easy to implement TS's with one or two out-of-line symbols. (Ex. PMRs)

`c++experimental` provides NO ABI compatibility. Symbols can freely be added/removed/changed without concern for ABI stability.
I will add documentation for this after landing this patch (but before adding anything to it).

`c++experimental` only builds as a static library. By default CMake will build/test this library but will *NOT* install it.

This patch adds the CMake and LIT logic needed to build/test the new library. Once this lands I plan on using it to implement parts of `<experimental/memory_resource>`.



Reviewers: mclow.lists

Subscribers: cfe-commits, theraven, krememek, dexonsmith, bcraig, beanz, danalbert

Differential Revision: http://reviews.llvm.org/D19856

llvm-svn: 268443

libcxx/CMakeLists.txt

@@ -52,14 +52,15 @@ MACRO_ENSURE_OUT_OF_SOURCE_BUILD(
 # Basic options ---------------------------------------------------------------
 option(LIBCXX_ENABLE_ASSERTIONS "Enable assertions independent of build mode." ON)
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
-
+option(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY "Build libc++experimental.a" ON)
 option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
 option(LIBCXX_INCLUDE_DOCS "Build the libc++ documentation." ${LLVM_INCLUDE_DOCS})
 set(LIBCXX_LIBDIR_SUFFIX "${LLVM_LIBDIR_SUFFIX}" CACHE STRING
     "Define suffix of library directory name (32/64)")
 option(LIBCXX_INSTALL_HEADERS "Install the libc++ headers." ON)
 option(LIBCXX_INSTALL_LIBRARY "Install the libc++ library." ON)
 option(LIBCXX_INSTALL_SUPPORT_HEADERS "Install libc++ support headers." ON)
+option(LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY "Install libc++experimental.a" OFF)
 set(LIBCXX_ABI_VERSION 1 CACHE STRING "ABI version of libc++.")
 option(LIBCXX_ABI_UNSTABLE "Unstable ABI of libc++." OFF)
 

libcxx/lib/CMakeLists.txt

@@ -138,6 +138,17 @@ set_target_properties(cxx
     SOVERSION     "${LIBCXX_ABI_VERSION}"
   )
 
+if (LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY)
+  file(GLOB LIBCXX_EXPERIMENTAL_SOURCES ../src/experimental/*.cpp)
+  add_library(cxx_experimental STATIC ${LIBCXX_EXPERIMENTAL_SOURCES})
+  target_link_libraries(cxx_experimental cxx)
+  set_target_properties(cxx_experimental
+    PROPERTIES
+      COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
+      OUTPUT_NAME   "c++experimental"
+  )
+endif()
+
 # Generate a linker script inplace of a libc++.so symlink. Rerun this command
 # after cxx builds.
 if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
@@ -160,7 +171,10 @@ if (LIBCXX_ENABLE_ABI_LINKER_SCRIPT)
 endif()
 
 if (LIBCXX_INSTALL_LIBRARY)
-  install(TARGETS cxx
+  if (LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY)
+    set(experimental_lib cxx_experimental)
+  endif()
+  install(TARGETS cxx ${experimental_lib}
     LIBRARY DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
     ARCHIVE DESTINATION lib${LIBCXX_LIBDIR_SUFFIX} COMPONENT libcxx
     )
@@ -180,11 +194,16 @@ if (NOT CMAKE_CONFIGURATION_TYPES AND (LIBCXX_INSTALL_LIBRARY OR
     if(LIBCXX_INSTALL_LIBRARY)
       set(lib_install_target cxx)
     endif()
+    if (LIBCXX_INSTALL_EXPERIMENTAL_LIBRARY)
+      set(experimental_lib_install_target cxx_experimental)
+    endif()
     if(LIBCXX_INSTALL_HEADERS)
       set(header_install_target install-libcxx-headers)
     endif()
     add_custom_target(install-libcxx
-                      DEPENDS ${lib_install_target} ${header_install_target}
+                      DEPENDS ${lib_install_target}
+                              ${experimental_lib_install_target}
+                              ${header_install_target}
                       COMMAND "${CMAKE_COMMAND}"
                       -DCMAKE_INSTALL_COMPONENT=libcxx
                       -P "${LIBCXX_BINARY_DIR}/cmake_install.cmake")

libcxx/src/experimental/placeholder.cpp

@@ -0,0 +1,14 @@
+//===--------------------------- TODO.cpp ---------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "experimental/__config"
+
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+
+_LIBCPP_END_NAMESPACE_LFTS

libcxx/test/CMakeLists.txt

@@ -10,6 +10,7 @@ set(LIBCXX_LIT_VARIANT "libcxx" CACHE STRING
     "Configuration variant to use for LIT.")
 
 pythonize_bool(LIBCXX_ENABLE_EXCEPTIONS)
+pythonize_bool(LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY)
 pythonize_bool(LIBCXX_ENABLE_RTTI)
 pythonize_bool(LIBCXX_ENABLE_SHARED)
 pythonize_bool(LIBCXX_BUILD_32_BITS)

libcxx/test/libcxx/test/config.py

@@ -456,6 +456,10 @@ def configure_link_flags_abi_library_path(self):
                                     '-Wl,-rpath,' + self.abi_library_root]
 
     def configure_link_flags_cxx_library(self):
+        libcxx_experimental = self.get_lit_bool('enable_experimental', default=False)
+        if libcxx_experimental:
+            self.config.available_features.add('c++experimental')
+            self.cxx.link_flags += ['-lc++experimental']
         libcxx_shared = self.get_lit_bool('enable_shared', default=True)
         if libcxx_shared:
             self.cxx.link_flags += ['-lc++']

libcxx/test/lit.site.cfg.in

@@ -5,6 +5,7 @@ config.libcxx_src_root          = "@LIBCXX_SOURCE_DIR@"
 config.libcxx_obj_root          = "@LIBCXX_BINARY_DIR@"
 config.cxx_library_root         = "@LIBCXX_LIBRARY_DIR@"
 config.enable_exceptions        = "@LIBCXX_ENABLE_EXCEPTIONS@"
+config.enable_experimental      = "@LIBCXX_ENABLE_EXPERIMENTAL_LIBRARY@"
 config.enable_rtti              = "@LIBCXX_ENABLE_RTTI@"
 config.enable_shared            = "@LIBCXX_ENABLE_SHARED@"
 config.enable_32bit             = "@LIBCXX_BUILD_32_BITS@"