Index: lib/Frontend/ASTUnit.cpp
===================================================================
--- lib/Frontend/ASTUnit.cpp
+++ lib/Frontend/ASTUnit.cpp
@@ -100,7 +100,8 @@
 static std::unique_ptr<llvm::MemoryBuffer>
 getBufferForFileHandlingRemapping(const CompilerInvocation &Invocation,
                                   vfs::FileSystem *VFS,
-                                  StringRef FilePath) {
+                                  StringRef FilePath,
+                                  bool isVolatile) {
   const auto &PreprocessorOpts = Invocation.getPreprocessorOpts();
 
   // Try to determine if the main file has been remapped, either from the
@@ -120,7 +121,8 @@
         llvm::sys::fs::UniqueID MID = MPathStatus->getUniqueID();
         if (MainFileID == MID) {
           // We found a remapping. Try to load the resulting, remapped source.
-          BufferOwner = valueOrNull(VFS->getBufferForFile(RF.second));
+          BufferOwner = valueOrNull(
+              VFS->getBufferForFile(RF.second, -1, true, isVolatile));
           if (!BufferOwner)
             return nullptr;
         }
@@ -145,7 +147,8 @@
 
   // If the main source file was not remapped, load it now.
   if (!Buffer && !BufferOwner) {
-    BufferOwner = valueOrNull(VFS->getBufferForFile(FilePath));
+    BufferOwner =
+        valueOrNull(VFS->getBufferForFile(FilePath, -1, true, isVolatile));
     if (!BufferOwner)
       return nullptr;
   }
@@ -1231,7 +1234,7 @@
       PreambleInvocationIn.getFrontendOpts().Inputs[0].getFile();
   std::unique_ptr<llvm::MemoryBuffer> MainFileBuffer =
       getBufferForFileHandlingRemapping(PreambleInvocationIn, VFS.get(),
-                                        MainFilePath);
+                                        MainFilePath, UserFilesAreVolatile);
   if (!MainFileBuffer)
     return nullptr;