3 files changed, 39 insertions, 29 deletions

diff --git a/clang/lib/Basic/FileManager.cpp b/clang/lib/Basic/FileManager.cpp
index 4330c7ac61c..cc6c2613fb3 100644
--- a/clang/lib/Basic/FileManager.cpp
+++ b/clang/lib/Basic/FileManager.cpp
@@ -390,6 +390,25 @@ FileManager::getVirtualFile(StringRef Filename, off_t Size,
   return UFE;
 }
 
+llvm::Optional<FileEntryRef> FileManager::getBypassFile(FileEntryRef VF) {
+  // Stat of the file and return nullptr if it doesn't exist.
+  llvm::vfs::Status Status;
+  if (getStatValue(VF.getName(), Status, /*isFile=*/true, /*F=*/nullptr))
+    return None;
+
+  // Fill it in from the stat.
+  BypassFileEntries.push_back(std::make_unique<FileEntry>());
+  const FileEntry &VFE = VF.getFileEntry();
+  FileEntry &BFE = *BypassFileEntries.back();
+  BFE.Name = VFE.getName();
+  BFE.Size = Status.getSize();
+  BFE.Dir = VFE.Dir;
+  BFE.ModTime = llvm::sys::toTimeT(Status.getLastModificationTime());
+  BFE.UID = NextFileUID++;
+  BFE.IsValid = true;
+  return FileEntryRef(VF.getName(), BFE);
+}
+
 bool FileManager::FixupRelativePath(SmallVectorImpl<char> &path) const {
   StringRef pathRef(path.data(), path.size());
 
@@ -515,12 +534,6 @@ void FileManager::GetUniqueIDMapping(
     UIDToFiles[VFE->getUID()] = VFE.get();
 }
 
-void FileManager::modifyFileEntry(FileEntry *File,
-                                  off_t Size, time_t ModificationTime) {
-  File->Size = Size;
-  File->ModTime = ModificationTime;
-}
-
 StringRef FileManager::getCanonicalName(const DirectoryEntry *Dir) {
   // FIXME: use llvm::sys::fs::canonical() when it gets implemented
   llvm::DenseMap<const DirectoryEntry *, llvm::StringRef>::iterator Known
diff --git a/clang/lib/Basic/SourceManager.cpp b/clang/lib/Basic/SourceManager.cpp
index d49d594e290..58b95289eaf 100644
--- a/clang/lib/Basic/SourceManager.cpp
+++ b/clang/lib/Basic/SourceManager.cpp
@@ -669,17 +669,19 @@ void SourceManager::overrideFileContents(const FileEntry *SourceFile,
   getOverriddenFilesInfo().OverriddenFiles[SourceFile] = NewFile;
 }
 
-void SourceManager::disableFileContentsOverride(const FileEntry *File) {
-  if (!isFileOverridden(File))
-    return;
-
-  const SrcMgr::ContentCache *IR = getOrCreateContentCache(File);
-  const_cast<SrcMgr::ContentCache *>(IR)->replaceBuffer(nullptr);
-  const_cast<SrcMgr::ContentCache *>(IR)->ContentsEntry = IR->OrigEntry;
+const FileEntry *
+SourceManager::bypassFileContentsOverride(const FileEntry &File) {
+  assert(isFileOverridden(&File));
+  llvm::Optional<FileEntryRef> BypassFile =
+      FileMgr.getBypassFile(FileEntryRef(File.getName(), File));
+
+  // If the file can't be found in the FS, give up.
+  if (!BypassFile)
+    return nullptr;
 
-  assert(OverriddenFilesInfo);
-  OverriddenFilesInfo->OverriddenFiles.erase(File);
-  OverriddenFilesInfo->OverriddenFilesWithBuffer.erase(File);
+  const FileEntry *FE = &BypassFile->getFileEntry();
+  (void)getOrCreateContentCache(FE);
+  return FE;
 }
 
 void SourceManager::setFileIsTransient(const FileEntry *File) {
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index aaa59fcf506..10b2a5c4f9d 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -2315,19 +2315,14 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
   if ((!Overridden && !Transient) && SM.isFileOverridden(File)) {
     if (Complain)
       Error(diag::err_fe_pch_file_overridden, Filename);
-    // After emitting the diagnostic, recover by disabling the override so
-    // that the original file will be used.
-    //
-    // FIXME: This recovery is just as broken as the original state; there may
-    // be another precompiled module that's using the overridden contents, or
-    // we might be half way through parsing it. Instead, we should treat the
-    // overridden contents as belonging to a separate FileEntry.
-    SM.disableFileContentsOverride(File);
-    // The FileEntry is a virtual file entry with the size of the contents
-    // that would override the original contents. Set it to the original's
-    // size/time.
-    FileMgr.modifyFileEntry(const_cast<FileEntry*>(File),
-                            StoredSize, StoredTime);
+
+    // After emitting the diagnostic, bypass the overriding file to recover
+    // (this creates a separate FileEntry).
+    File = SM.bypassFileContentsOverride(*File);
+    if (!File) {
+      F.InputFilesLoaded[ID - 1] = InputFile::getNotFound();
+      return InputFile();
+    }
   }
 
   bool IsOutOfDate = false;