Index: llvm/trunk/include/llvm/DebugInfo/PDB/PDBTypes.h
===================================================================
--- llvm/trunk/include/llvm/DebugInfo/PDB/PDBTypes.h
+++ llvm/trunk/include/llvm/DebugInfo/PDB/PDBTypes.h
@@ -320,7 +320,8 @@
 
 enum class PDB_ErrorCode {
   Success,
-  NoPdbImpl,
+  NoDiaSupport,
+  CouldNotCreateImpl,
   InvalidPath,
   InvalidFileFormat,
   InvalidParameter,
Index: llvm/trunk/lib/DebugInfo/PDB/DIA/DIASession.cpp
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/DIA/DIASession.cpp
+++ llvm/trunk/lib/DebugInfo/PDB/DIA/DIASession.cpp
@@ -24,17 +24,18 @@
 
 namespace {
 
-bool LoadDIA(CComPtr<IDiaDataSource>& DiaDataSource) {
+PDB_ErrorCode LoadDIA(CComPtr<IDiaDataSource> &DiaDataSource) {
   if (SUCCEEDED(CoCreateInstance(CLSID_DiaSource, nullptr, CLSCTX_INPROC_SERVER,
                                  IID_IDiaDataSource,
                                  reinterpret_cast<LPVOID *>(&DiaDataSource))))
-    return true;
+    return PDB_ErrorCode::Success;
 
   // If the CoCreateInstance call above failed, msdia*.dll is not registered.
   // Try loading the DLL corresponding to the #included DIA SDK.
 #if !defined(_MSC_VER)
-  return false;
-#else
+  return PDB_ErrorCode::NoDiaSupport;
+#endif
+
   const wchar_t *msdia_dll = nullptr;
 #if _MSC_VER == 1900
   msdia_dll = L"msdia140.dll"; // VS2015
@@ -43,10 +44,12 @@
 #else
 #error "Unknown Visual Studio version."
 #endif
-  return msdia_dll &&
-         SUCCEEDED(NoRegCoCreate(msdia_dll, CLSID_DiaSource, IID_IDiaDataSource,
-                                 reinterpret_cast<LPVOID *>(&DiaDataSource)));
-#endif
+
+  if (SUCCEEDED(NoRegCoCreate(msdia_dll, CLSID_DiaSource, IID_IDiaDataSource,
+                              reinterpret_cast<LPVOID *>(&DiaDataSource))))
+    return PDB_ErrorCode::Success;
+  else
+    return PDB_ErrorCode::CouldNotCreateImpl;
 }
 
 }
@@ -59,8 +62,9 @@
   CComPtr<IDiaSession> DiaSession;
 
   // We assume that CoInitializeEx has already been called by the executable.
-  if (!LoadDIA(DiaDataSource))
-    return PDB_ErrorCode::NoPdbImpl;
+  PDB_ErrorCode result = LoadDIA(DiaDataSource);
+  if (result != PDB_ErrorCode::Success)
+    return result;
 
   llvm::SmallVector<UTF16, 128> Path16;
   if (!llvm::convertUTF8ToUTF16String(Path, Path16))
@@ -98,8 +102,9 @@
   CComPtr<IDiaSession> DiaSession;
 
   // We assume that CoInitializeEx has already been called by the executable.
-  if (!LoadDIA(DiaDataSource))
-    return PDB_ErrorCode::NoPdbImpl;
+  PDB_ErrorCode result = LoadDIA(DiaDataSource);
+  if (result != PDB_ErrorCode::Success)
+    return result;
 
   llvm::SmallVector<UTF16, 128> Path16;
   if (!llvm::convertUTF8ToUTF16String(Path, Path16))
Index: llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
===================================================================
--- llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
+++ llvm/trunk/lib/DebugInfo/PDB/PDB.cpp
@@ -26,7 +26,7 @@
 #if HAVE_DIA_SDK
   return DIASession::createFromPdb(Path, Session);
 #endif
-  return PDB_ErrorCode::NoPdbImpl;
+  return PDB_ErrorCode::NoDiaSupport;
 }
 
 PDB_ErrorCode llvm::loadDataForEXE(PDB_ReaderType Type, StringRef Path,
@@ -35,5 +35,5 @@
 #if HAVE_DIA_SDK
   return DIASession::createFromExe(Path, Session);
 #endif
-  return PDB_ErrorCode::NoPdbImpl;
+  return PDB_ErrorCode::NoDiaSupport;
 }
Index: llvm/trunk/tools/llvm-pdbdump/llvm-pdbdump.cpp
===================================================================
--- llvm/trunk/tools/llvm-pdbdump/llvm-pdbdump.cpp
+++ llvm/trunk/tools/llvm-pdbdump/llvm-pdbdump.cpp
@@ -624,8 +624,14 @@
   switch (Error) {
   case PDB_ErrorCode::Success:
     break;
-  case PDB_ErrorCode::NoPdbImpl:
-    outs() << "Reading PDBs is not supported on this platform.\n";
+  case PDB_ErrorCode::NoDiaSupport:
+    outs() << "LLVM was not compiled with support for DIA.  This usually means "
+              "that either LLVM was not compiled with MSVC, or your MSVC "
+              "installation is corrupt.\n";
+    return;
+  case PDB_ErrorCode::CouldNotCreateImpl:
+    outs() << "Failed to connect to DIA at runtime.  Verify that Visual Studio "
+              "is properly installed, or that msdiaXX.dll is in your PATH.\n";
     return;
   case PDB_ErrorCode::InvalidPath:
     outs() << "Unable to load PDB at '" << Path