[CMake] Introduce a LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY flag.

On Darwin it is currently impossible to build LLVM with modules
because the Darwin system module map is not compatible with
-fmodules-local-submodule-visibility at this point in time.  This
patch makes the flag optional and off by default on Darwin so it
becomes possible to build LLVM with modules again.

http://reviews.llvm.org/D21827
rdar://problem/27019000

llvm-svn: 274196

2 files changed, 16 insertions, 2 deletions

diff --git a/llvm/CMakeLists.txt b/llvm/CMakeLists.txt
index a83d47761a4..f779c6f8031 100644
--- a/llvm/CMakeLists.txt
+++ b/llvm/CMakeLists.txt
@@ -283,6 +283,11 @@ include(AddLLVMDefinitions)
 option(LLVM_ENABLE_PIC "Build Position-Independent Code" ON)
 option(LLVM_ENABLE_WARNINGS "Enable compiler warnings." ON)
 option(LLVM_ENABLE_MODULES "Compile with C++ modules enabled." OFF)
+if(${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+  option(LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY "Compile with -fmodules-local-submodule-visibility." OFF)
+else()
+  option(LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY "Compile with -fmodules-local-submodule-visibility." ON)
+endif()
 option(LLVM_ENABLE_CXX1Y "Compile with C++1y enabled." OFF)
 option(LLVM_ENABLE_LIBCXX "Use libc++ if available." OFF)
 option(LLVM_ENABLE_LIBCXXABI "Use libc++abi when using libc++." OFF)
diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
index 493c1c9eb71..d4587913522 100644
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -465,7 +465,16 @@ elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
   endif()
   if (LLVM_ENABLE_MODULES)
     set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
-    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fmodules -Xclang -fmodules-local-submodule-visibility -fmodules-cache-path=module.cache")
+    set(module_flags "-fmodules -Xclang -fmodules-cache-path=module.cache")
+    if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
+      # On Darwin -fmodules does not imply -fcxx-modules.
+      set(module_flags "${module_flags} -fcxx-modules")
+    endif()
+    if (LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY)
+      set(module_flags "${module_flags} -fmodules-local-submodule-visibility")
+    endif()
+    set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} ${module_flags}")
+
     # Check that we can build code with modules enabled, and that repeatedly
     # including <cassert> still manages to respect NDEBUG properly.
     CHECK_CXX_SOURCE_COMPILES("#undef NDEBUG
@@ -476,7 +485,7 @@ elseif( LLVM_COMPILER_IS_GCC_COMPATIBLE )
                                CXX_SUPPORTS_MODULES)
     set(CMAKE_REQUIRED_FLAGS ${OLD_CMAKE_REQUIRED_FLAGS})
     if (CXX_SUPPORTS_MODULES)
-      append_if(CXX_SUPPORTS_MODULES "-fmodules -Xclang -fmodules-local-submodule-visibility -fmodules-cache-path=module.cache" CMAKE_CXX_FLAGS)
+      append("${module_flags}" CMAKE_CXX_FLAGS)
     else()
       message(FATAL_ERROR "LLVM_ENABLE_MODULES is not supported by this compiler")
     endif()