[PATCH] [CMake] Add -stdlib=libc++ to host Clang build flags before performing any header search

[Alexey Samsonov]

Hi chapuni,

If LLVM_ENABLE_LIBCXX is specified, we should append -stdlib=libc++ to build
flags as early as possible, in particular, before we check for header presence
(as -stdlib=libc++ modifies header lookup rules). Otherwise we can find a header
at configure time (w/o -stdlib=libc++) but fail to find it at build time
(with -stdlib=libc++). See PR18569 for more details.

http://llvm-reviews.chandlerc.com/D2626

Files:
  CMakeLists.txt
  cmake/config-ix.cmake
  cmake/modules/HandleLLVMOptions.cmake

Index: CMakeLists.txt
===================================================================
--- CMakeLists.txt
+++ CMakeLists.txt
@@ -272,6 +272,14 @@
 option (LLVM_INCLUDE_DOCS "Generate build targets for llvm documentation." ON)
 option (LLVM_ENABLE_DOXYGEN "Use doxygen to generate llvm documentation." OFF)
 
+if( CMAKE_COMPILER_IS_GNUCXX )
+  set(LLVM_COMPILER_IS_GCC_COMPATIBLE ON)
+elseif( MSVC )
+  set(LLVM_COMPILER_IS_GCC_COMPATIBLE OFF)
+elseif( "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
+  set(LLVM_COMPILER_IS_GCC_COMPATIBLE ON)
+endif()
+
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
 # first cmake run
Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -34,6 +34,25 @@
     " ${variable})
 endfunction()
 
+function(append_if condition value)
+  if (${condition})
+    foreach(variable ${ARGN})
+      set(${variable} "${${variable}} ${value}" PARENT_SCOPE)
+    endforeach(variable)
+  endif()
+endfunction()
+
+include(CheckCXXCompilerFlag)
+if( LLVM_COMPILER_IS_GCC_COMPATIBLE )
+  if( LLVM_ENABLE_LIBCXX )
+    check_cxx_compiler_flag("-stdlib=libc++" CXX_SUPPORTS_STDLIB)
+    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_CXX_FLAGS)
+    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_EXE_LINKER_FLAGS)
+    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_SHARED_LINKER_FLAGS)
+    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_MODULE_LINKER_FLAGS)
+  endif()
+endif()
+
 # include checks
 check_include_file_cxx(cxxabi.h HAVE_CXXABI_H)
 check_include_file(dirent.h HAVE_DIRENT_H)
@@ -316,8 +335,6 @@
   endif ()
 endif ()
 
-include(CheckCXXCompilerFlag)
-
 check_cxx_compiler_flag("-Wno-variadic-macros" SUPPORTS_NO_VARIADIC_MACROS_FLAG)
 
 set(USE_NO_MAYBE_UNINITIALIZED 0)
Index: cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- cmake/modules/HandleLLVMOptions.cmake
+++ cmake/modules/HandleLLVMOptions.cmake
@@ -6,14 +6,6 @@
 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
-if( CMAKE_COMPILER_IS_GNUCXX )
-  set(LLVM_COMPILER_IS_GCC_COMPATIBLE ON)
-elseif( MSVC )
-  set(LLVM_COMPILER_IS_GCC_COMPATIBLE OFF)
-elseif( "${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" )
-  set(LLVM_COMPILER_IS_GCC_COMPATIBLE ON)
-endif()
-
 if(NOT LLVM_FORCE_USE_OLD_TOOLCHAIN)
   if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
     if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 4.7)
@@ -291,13 +283,6 @@
     check_cxx_compiler_flag("-std=c++11" CXX_SUPPORTS_CXX11)
     append_if(CXX_SUPPORTS_CXX11 "-std=c++11" CMAKE_CXX_FLAGS)
   endif (LLVM_ENABLE_CXX11)
-  if(LLVM_ENABLE_LIBCXX)
-    check_cxx_compiler_flag("-stdlib=libc++" CXX_SUPPORTS_STDLIB)
-    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_CXX_FLAGS)
-    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_EXE_LINKER_FLAGS)
-    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_SHARED_LINKER_FLAGS)
-    append_if(CXX_SUPPORTS_STDLIB "-stdlib=libc++" CMAKE_MODULE_LINKER_FLAGS)
-  endif ()
 endif( MSVC )
 
 macro(append_common_sanitizer_flags)
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