Index: llvm/trunk/cmake/config-ix.cmake
===================================================================
--- llvm/trunk/cmake/config-ix.cmake
+++ llvm/trunk/cmake/config-ix.cmake
@@ -450,8 +450,15 @@
   else()
     set(HAVE_DIA_SDK 0)
   endif()
+
+  option(LLVM_ENABLE_DIA_SDK "Use MSVC DIA SDK for debugging if available."
+                             ${HAVE_DIA_SDK})
+
+  if(LLVM_ENABLE_DIA_SDK AND NOT HAVE_DIA_SDK)
+    message(FATAL_ERROR "DIA SDK not found. If you have both VS 2012 and 2013 installed, you may need to uninstall the former and re-install the latter afterwards.")
+  endif()
 else()
-  set(HAVE_DIA_SDK 0)
+  set(LLVM_ENABLE_DIA_SDK 0)
 endif( MSVC )
 
 # FIXME: Signal handler return type, currently hardcoded to 'void'
Index: llvm/trunk/cmake/modules/LLVMConfig.cmake.in
===================================================================
--- llvm/trunk/cmake/modules/LLVMConfig.cmake.in
+++ llvm/trunk/cmake/modules/LLVMConfig.cmake.in
@@ -37,6 +37,8 @@
 
 set(LLVM_ENABLE_ZLIB @LLVM_ENABLE_ZLIB@)
 
+set(LLVM_ENABLE_DIA_SDK @LLVM_ENABLE_DIA_SDK@)
+
 set(LLVM_NATIVE_ARCH @LLVM_NATIVE_ARCH@)
 
 set(LLVM_ENABLE_PIC @LLVM_ENABLE_PIC@)
Index: llvm/trunk/docs/CMake.rst
===================================================================
--- llvm/trunk/docs/CMake.rst
+++ llvm/trunk/docs/CMake.rst
@@ -368,6 +368,10 @@
   Enable building with zlib to support compression/uncompression in LLVM tools.
   Defaults to ON.
 
+**LLVM_ENABLE_DIA_SDK**:BOOL
+  Enable building with MSVC DIA SDK for PDB debugging support. Available
+  only with MSVC. Defaults to ON.
+
 **LLVM_USE_SANITIZER**:STRING
   Define the sanitizer used to build LLVM binaries and tests. Possible values
   are ``Address``, ``Memory``, ``MemoryWithOrigins``, ``Undefined``, ``Thread``,
Index: llvm/trunk/include/llvm/Config/config.h.cmake
===================================================================
--- llvm/trunk/include/llvm/Config/config.h.cmake
+++ llvm/trunk/include/llvm/Config/config.h.cmake
@@ -39,7 +39,7 @@
 #cmakedefine01 HAVE_DECL_STRERROR_S
 
 /* Define to 1 if you have the DIA SDK installed, and to 0 if you don't. */
-#cmakedefine01 HAVE_DIA_SDK
+#cmakedefine01 LLVM_ENABLE_DIA_SDK
 
 /* Define to 1 if you have the <dirent.h> header file, and it defines `DIR'.
    */
Index: llvm/trunk/lib/DebugInfo/PDB/CMakeLists.txt
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/CMakeLists.txt
+++ llvm/trunk/lib/DebugInfo/PDB/CMakeLists.txt
@@ -3,7 +3,7 @@
   source_group(${group} FILES ${ARGN})
 endmacro()
 
-if(HAVE_DIA_SDK)
+if(LLVM_ENABLE_DIA_SDK)
   include_directories(${MSVC_DIA_SDK_DIR}/include)
   set(LIBPDB_LINK_FOLDERS "${MSVC_DIA_SDK_DIR}\\lib")
   if (CMAKE_SIZEOF_VOID_P EQUAL 8)
Index: llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
+++ llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
@@ -14,7 +14,7 @@
 #include "llvm/DebugInfo/PDB/GenericError.h"
 #include "llvm/DebugInfo/PDB/IPDBSession.h"
 #include "llvm/DebugInfo/PDB/PDB.h"
-#if HAVE_DIA_SDK
+#if LLVM_ENABLE_DIA_SDK
 #include "llvm/DebugInfo/PDB/DIA/DIASession.h"
 #endif
 #include "llvm/DebugInfo/PDB/Raw/RawSession.h"
@@ -30,7 +30,7 @@
   if (Type == PDB_ReaderType::Raw)
     return RawSession::createFromPdb(Path, Session);
 
-#if HAVE_DIA_SDK
+#if LLVM_ENABLE_DIA_SDK
   return DIASession::createFromPdb(Path, Session);
 #else
   return llvm::make_error<GenericError>("DIA is not installed on the system");
@@ -43,7 +43,7 @@
   if (Type == PDB_ReaderType::Raw)
     return RawSession::createFromExe(Path, Session);
 
-#if HAVE_DIA_SDK
+#if LLVM_ENABLE_DIA_SDK
   return DIASession::createFromExe(Path, Session);
 #else
   return llvm::make_error<GenericError>("DIA is not installed on the system");
Index: llvm/trunk/test/lit.site.cfg.in
===================================================================
--- llvm/trunk/test/lit.site.cfg.in
+++ llvm/trunk/test/lit.site.cfg.in
@@ -36,7 +36,7 @@
 config.llvm_use_sanitizer = "@LLVM_USE_SANITIZER@"
 config.have_zlib = "@HAVE_LIBZ@"
 config.have_libxar = "@HAVE_LIBXAR@"
-config.have_dia_sdk = @HAVE_DIA_SDK@
+config.have_dia_sdk = @LLVM_ENABLE_DIA_SDK@
 config.enable_ffi = "@LLVM_ENABLE_FFI@"
 config.test_examples = "@ENABLE_EXAMPLES@"