Index: lib/Basic/FileManager.cpp
===================================================================
--- lib/Basic/FileManager.cpp
+++ lib/Basic/FileManager.cpp
@@ -316,10 +316,14 @@
   UFE.File = std::move(F);
   UFE.IsValid = true;
 
-  SmallString<128> RealPathName;
-  if (!FS->getRealPath(InterndFileName, RealPathName))
-    UFE.RealPathName = RealPathName.str();
-
+  llvm::SmallString<128> AbsPath(InterndFileName);
+  // This is not the same as `VFS::getRealPath()`, which resolves symlinks but
+  // can be very expensive on real file systems.
+  // FIXME: the semantic of RealPathName is unclear, and the name might be
+  // misleading. We need to clean up the interface here.
+  makeAbsolutePath(AbsPath);
+  llvm::sys::path::remove_dots(AbsPath, /*remove_dot_dot=*/true);
+  UFE.RealPathName = AbsPath.str();
   return &UFE;
 }