Index: lib/Frontend/CompilerInstance.cpp
===================================================================
--- lib/Frontend/CompilerInstance.cpp
+++ lib/Frontend/CompilerInstance.cpp
@@ -742,7 +742,7 @@
 
   // Figure out where to get and map in the main file.
   if (InputFile != "-") {
-    const FileEntry *File;
+    const FileEntry *File = nullptr;
     if (Opts.FindPchSource.empty()) {
       File = FileMgr.getFile(InputFile, /*OpenFile=*/true);
     } else {
@@ -760,13 +760,14 @@
       SmallVector<std::pair<const FileEntry *, const DirectoryEntry *>, 16>
           Includers;
       Includers.push_back(std::make_pair(FindFile, FindFile->getDir()));
-      File = HS->LookupFile(InputFile, SourceLocation(), /*isAngled=*/false,
-                            /*FromDir=*/nullptr,
-                            /*CurDir=*/UnusedCurDir, Includers,
-                            /*SearchPath=*/nullptr,
-                            /*RelativePath=*/nullptr,
-                            /*RequestingModule=*/nullptr,
-                            /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
+      if (HS)
+        File = HS->LookupFile(InputFile, SourceLocation(), /*isAngled=*/false,
+                              /*FromDir=*/nullptr,
+                              /*CurDir=*/UnusedCurDir, Includers,
+                              /*SearchPath=*/nullptr,
+                              /*RelativePath=*/nullptr,
+                              /*RequestingModule=*/nullptr,
+                              /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
       // Also add the header to /showIncludes output.
       if (File)
         DepOpts.ShowIncludesPretendHeader = File->getName();