Update the documentation and CMake file for Visual Studio generators.

By default, CMake uses a 32-bit toolchain, even when on a 64-bit platform targeting a 64-bit build. However, due to the size of the binaries involved, this can cause linker instabilities (such as the linker running out of memory). Guide people to the correct solution to get CMake to use the native toolchain.

llvm-svn: 303912

Author: AaronBallman

llvm/CMakeLists.txt

@@ -44,6 +44,13 @@ if (NOT PACKAGE_VERSION)
     "${LLVM_VERSION_MAJOR}.${LLVM_VERSION_MINOR}.${LLVM_VERSION_PATCH}${LLVM_VERSION_SUFFIX}")
 endif()
 
+if ((CMAKE_GENERATOR MATCHES "Visual Studio") AND (CMAKE_GENERATOR_TOOLSET STREQUAL ""))
+  message(WARNING "Visual Studio generators use the x86 host compiler by "
+                  "default, even for 64-bit targets. This can result in linker "
+                  "instability and out of memory errors. To use the 64-bit "
+                  "host compiler, pass -Thost=x64 on the CMake command line.")
+endif()
+
 project(LLVM
   ${cmake_3_0_PROJ_VERSION}
   ${cmake_3_0_LANGUAGES}

llvm/docs/GettingStartedVS.rst

@@ -100,6 +100,10 @@ Here's the short story for getting up and running quickly with LLVM:
    * CMake generates project files for all build types. To select a specific
      build type, use the Configuration manager from the VS IDE or the 
      ``/property:Configuration`` command line option when using MSBuild.
+   * By default, the Visual Studio project files generated by CMake use the
+     32-bit toolset. If you are developing on a 64-bit version of Windows and
+     want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
+     generating the Visual Studio solution. This requires CMake 3.8.0 or later.
 
 6. Start Visual Studio