Index: clang/include/clang/Basic/SourceManager.h
===================================================================
--- clang/include/clang/Basic/SourceManager.h
+++ clang/include/clang/Basic/SourceManager.h
@@ -814,7 +814,7 @@
   /// Returns true when the given FileEntry corresponds to the main file.
   ///
   /// The main file should be set prior to calling this function.
-  bool isMainFile(FileEntryRef SourceFile);
+  bool isMainFile(const FileEntry &SourceFile);
 
   /// Set the file ID for the precompiled preamble.
   void setPreambleFileID(FileID Preamble) {
Index: clang/lib/Basic/SourceManager.cpp
===================================================================
--- clang/lib/Basic/SourceManager.cpp
+++ clang/lib/Basic/SourceManager.cpp
@@ -343,12 +343,11 @@
   createExpansionLoc(SourceLocation(), SourceLocation(), SourceLocation(), 1);
 }
 
-bool SourceManager::isMainFile(FileEntryRef SourceFile) {
+bool SourceManager::isMainFile(const FileEntry &SourceFile) {
   assert(MainFileID.isValid() && "expected initialized SourceManager");
-  auto FE = getFileEntryRefForID(MainFileID);
-  if (!FE)
-    return false;
-  return FE->getUID() == SourceFile.getUID();
+  if (auto *FE = getFileEntryForID(MainFileID))
+    return FE->getUID() == SourceFile.getUID();
+  return false;
 }
 
 void SourceManager::initializeForReplay(const SourceManager &Old) {
Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -2061,7 +2061,7 @@
   // some directives (e.g. #endif of a header guard) will never be seen.
   // Since this will lead to confusing errors, avoid the inclusion.
   if (Action == Enter && File && PreambleConditionalStack.isRecording() &&
-      SourceMgr.isMainFile(*File)) {
+      SourceMgr.isMainFile(File->getFileEntry())) {
     Diag(FilenameTok.getLocation(),
          diag::err_pp_including_mainfile_in_preamble);
     return {ImportAction::None};
Index: clang/unittests/Basic/SourceManagerTest.cpp
===================================================================
--- clang/unittests/Basic/SourceManagerTest.cpp
+++ clang/unittests/Basic/SourceManagerTest.cpp
@@ -509,10 +509,9 @@
   FileID MainFileID = SourceMgr.getOrCreateFileID(SourceFile, SrcMgr::C_User);
   SourceMgr.setMainFileID(MainFileID);
 
-  EXPECT_TRUE(SourceMgr.isMainFile(FileEntryRef("mainFile.cpp", *SourceFile)));
-  EXPECT_TRUE(
-      SourceMgr.isMainFile(FileEntryRef("anotherName.cpp", *SourceFile)));
-  EXPECT_FALSE(SourceMgr.isMainFile(FileEntryRef("mainFile.cpp", *SecondFile)));
+  EXPECT_TRUE(SourceMgr.isMainFile(*SourceFile));
+  EXPECT_TRUE(SourceMgr.isMainFile(*SourceFile));
+  EXPECT_FALSE(SourceMgr.isMainFile(*SecondFile));
 }
 
 #endif