[libc++] [CMake] Link with /nodefaultlibs on Windows

Summary:
This patch attempts to fix the libc++ build/link so that it doesn't use an default C++ libraries on Windows.  This is needed to prevent linking to MSVC's STL library.

Additionally this patch changes libc++ so that it is always linked with the non-debug DLL's (e.g. `/MD`). This is needed so that the test suite can correctly link the same libraries without needing to know which configuration `c++.dll` was linked with.


Reviewers: compnerd, rnk, majnemer, kimgr, awson, halyavin, smeenai

Subscribers: cfe-commits, mgorny

Differential Revision: https://reviews.llvm.org/D28441

llvm-svn: 292001

Author: EricWF

libcxx/CMakeLists.txt

@@ -39,6 +39,12 @@ MACRO_ENSURE_OUT_OF_SOURCE_BUILD(
  build directory and run 'cmake /path/to/${PROJECT_NAME} [options]' there."
  )
 
+if (MSVC)
+  set(LIBCXX_TARGETING_MSVC ON)
+else()
+  set(LIBCXX_TARGETING_MSVC OFF)
+endif()
+
 #===============================================================================
 # Setup CMake Options
 #===============================================================================
@@ -377,6 +383,11 @@ if (NOT LIBCXX_STANDALONE_BUILD)
 endif()
 remove_flags(-stdlib=libc++ -stdlib=libstdc++)
 
+# FIXME: Remove all debug flags and flags that change which Windows
+# default libraries are linked. Currently we only support linking the
+# non-debug DLLs
+remove_flags("/D_DEBUG" "/MTd" "/MDd" "/MT" "/Md" "/RTC1")
+
 # FIXME(EricWF): See the FIXME on LIBCXX_ENABLE_PEDANTIC.
 # Remove the -pedantic flag and -Wno-pedantic and -pedantic-errors
 # so they don't get transformed into -Wno and -errors respectivly.
@@ -476,7 +487,7 @@ define_if(LIBCXX_ENABLE_ASSERTIONS -UNDEBUG)
 define_if_not(LIBCXX_ENABLE_ASSERTIONS -DNDEBUG)
 if (LIBCXX_ENABLE_ASSERTIONS)
   # MSVC doesn't like _DEBUG on release builds. See PR 4379.
-  define_if_not(MSVC -D_DEBUG)
+  define_if_not(LIBCXX_TARGETING_MSVC -D_DEBUG)
 endif()
 
 # Modules flags ===============================================================

libcxx/cmake/Modules/HandleLibcxxFlags.cmake

@@ -26,6 +26,10 @@ endmacro()
 # or added in other parts of LLVM's cmake configuration.
 macro(remove_flags)
   foreach(var ${ARGN})
+    string(REPLACE "${var}" "" CMAKE_CXX_FLAGS_DEBUG "${CMAKE_CXX_FLAGS_DEBUG}")
+    string(REPLACE "${var}" "" CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS_DEBUG}")
+    string(REPLACE "${var}" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_DEBUG}")
+    string(REPLACE "${var}" "" CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS_DEBUG}")
     string(REPLACE "${var}" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
     string(REPLACE "${var}" "" CMAKE_C_FLAGS "${CMAKE_C_FLAGS}")
     string(REPLACE "${var}" "" CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS}")

libcxx/lib/CMakeLists.txt

@@ -104,6 +104,17 @@ if (NOT WIN32)
 endif()
 add_link_flags_if_supported(-nodefaultlibs)
 
+if (LIBCXX_TARGETING_MSVC)
+  add_compile_flags(/Zl)
+  add_link_flags(/nodefaultlib)
+  add_library_flags(ucrt) # Universal C runtime
+  add_library_flags(vcruntime) # C++ runtime
+  add_library_flags(msvcrt) # C runtime startup files
+  # Required for standards-complaint wide character formatting functions
+  # (e.g. `printfw`/`scanfw`)
+  add_library_flags(iso_stdio_wide_specifiers)
+endif()
+
 if (LIBCXX_OSX_REEXPORT_SYSTEM_ABI_LIBRARY)
   if (NOT DEFINED LIBCXX_LIBCPPABI_VERSION)
     set(LIBCXX_LIBCPPABI_VERSION "2") # Default value

libcxx/test/libcxx/test/config.py

@@ -667,7 +667,7 @@ def configure_link_flags_abi_library(self):
             self.cxx.link_flags += ['-lcxxrt']
         elif cxx_abi == 'none' or cxx_abi == 'default':
             if self.is_windows:
-                self.cxx.link_flags += ['-lmsvcrtd']
+                self.cxx.link_flags += ['-lmsvcrt']
         else:
             self.lit_config.fatal(
                 'C++ ABI setting %s unsupported for tests' % cxx_abi)