[PATCH] D19992: [libcxx] Prefer C++14 over C++11 when building libc++experimental.

[Eric Fiselier via cfe-commits]

EricWF created this revision.
EricWF added a reviewer: mclow.lists.
EricWF added a subscriber: cfe-commits.

Currently libc++experimental builds with C++11. This patch changes that to C++14 when supported by the compiler. Although nothing currently requires C++14 the upcoming <experimental/memory_resource> implementation would benefit from it. [1]

Note that libc++.so continues to build with C++11 and is unaffected by this change.

[1] <experimental/memory_resource> provides global resources which must exist for the entire lifetime of the program. In order to ensure that a global resource can be used during program termination there destructors must never be invoked. The only way to do this, while also allowing "constant initialization", is to use a C++14 union.


http://reviews.llvm.org/D19992

Files:
  cmake/Modules/HandleLibcxxFlags.cmake
  lib/CMakeLists.txt

Index: lib/CMakeLists.txt
===================================================================
--- lib/CMakeLists.txt
+++ lib/CMakeLists.txt
@@ -142,9 +142,15 @@
   file(GLOB LIBCXX_EXPERIMENTAL_SOURCES ../src/experimental/*.cpp)
   add_library(cxx_experimental STATIC ${LIBCXX_EXPERIMENTAL_SOURCES})
   target_link_libraries(cxx_experimental cxx)
+
+  set(experimental_flags "${LIBCXX_COMPILE_FLAGS}")
+  check_flag_supported(-std=c++14)
+  if (NOT MSVC AND LIBCXX_SUPPORTS_STD_EQ_CXX14_FLAG)
+    string(REPLACE "-std=c++11" "-std=c++14" experimental_flags "${LIBCXX_COMPILE_FLAGS}")
+  endif()
   set_target_properties(cxx_experimental
     PROPERTIES
-      COMPILE_FLAGS "${LIBCXX_COMPILE_FLAGS}"
+      COMPILE_FLAGS "${experimental_flags}"
       OUTPUT_NAME   "c++experimental"
   )
 endif()
Index: cmake/Modules/HandleLibcxxFlags.cmake
===================================================================
--- cmake/Modules/HandleLibcxxFlags.cmake
+++ cmake/Modules/HandleLibcxxFlags.cmake
@@ -35,6 +35,11 @@
   endforeach()
 endmacro(remove_flags)
 
+macro(check_flag_supported flag)
+    mangle_name("${flag}" flagname)
+    check_cxx_compiler_flag("${flag}" "LIBCXX_SUPPORTS_${flagname}_FLAG")
+endmacro()
+
 # Add a macro definition if condition is true.
 macro(define_if condition def)
   if (${condition})


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D19992.56333.patch
Type: text/x-patch
Size: 1318 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20160505/8edf7136/attachment-0001.bin>