2 files changed, 30 insertions, 22 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index fa84b94b082..2defd38e27a 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -1259,7 +1259,8 @@ bool ASTReader::ReadSLocEntry(int ID) {
       = SourceMgr.getOrCreateContentCache(File,
                               /*isSystemFile=*/FileCharacter != SrcMgr::C_User);
     if (OverriddenBuffer && !ContentCache->BufferOverridden &&
-        ContentCache->ContentsEntry == ContentCache->OrigEntry) {
+        ContentCache->ContentsEntry == ContentCache->OrigEntry &&
+        !ContentCache->getRawBuffer()) {
       unsigned Code = SLocEntryCursor.ReadCode();
       Record.clear();
       unsigned RecCode = SLocEntryCursor.readRecord(Code, Record, &Blob);
@@ -1890,19 +1891,14 @@ ASTReader::readInputFileInfo(ModuleFile &F, unsigned ID) {
          "invalid record type for input file");
   (void)Result;
 
-  std::string Filename;
-  off_t StoredSize;
-  time_t StoredTime;
-  bool Overridden;
-
   assert(Record[0] == ID && "Bogus stored ID or offset");
-  StoredSize = static_cast<off_t>(Record[1]);
-  StoredTime = static_cast<time_t>(Record[2]);
-  Overridden = static_cast<bool>(Record[3]);
-  Filename = Blob;
-  ResolveImportedPath(F, Filename);
-
-  InputFileInfo R = { std::move(Filename), StoredSize, StoredTime, Overridden };
+  InputFileInfo R;
+  R.StoredSize = static_cast<off_t>(Record[1]);
+  R.StoredTime = static_cast<time_t>(Record[2]);
+  R.Overridden = static_cast<bool>(Record[3]);
+  R.Transient = static_cast<bool>(Record[4]);
+  R.Filename = Blob;
+  ResolveImportedPath(F, R.Filename);
   return R;
 }
 
@@ -1927,11 +1923,10 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
   off_t StoredSize = FI.StoredSize;
   time_t StoredTime = FI.StoredTime;
   bool Overridden = FI.Overridden;
+  bool Transient = FI.Transient;
   StringRef Filename = FI.Filename;
 
-  const FileEntry *File
-    = Overridden? FileMgr.getVirtualFile(Filename, StoredSize, StoredTime)
-                : FileMgr.getFile(Filename, /*OpenFile=*/false);
+  const FileEntry *File = FileMgr.getFile(Filename, /*OpenFile=*/false);
 
   // If we didn't find the file, resolve it relative to the
   // original directory from which this AST file was created.
@@ -1946,9 +1941,8 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
 
   // For an overridden file, create a virtual file with the stored
   // size/timestamp.
-  if (Overridden && File == nullptr) {
+  if ((Overridden || Transient) && File == nullptr)
     File = FileMgr.getVirtualFile(Filename, StoredSize, StoredTime);
-  }
 
   if (File == nullptr) {
     if (Complain) {
@@ -1974,6 +1968,11 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool 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
@@ -2024,8 +2023,10 @@ InputFile ASTReader::getInputFile(ModuleFile &F, unsigned ID, bool Complain) {
 
     IsOutOfDate = true;
   }
+  // FIXME: If the file is overridden and we've already opened it,
+  // issue an error (or split it into a separate FileEntry).
 
-  InputFile IF = InputFile(File, Overridden, IsOutOfDate);
+  InputFile IF = InputFile(File, Overridden || Transient, IsOutOfDate);
 
   // Note that we've loaded this input file.
   F.InputFilesLoaded[ID-1] = IF;
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 0b257a4a1b0..e6eb9be25e9 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -1485,6 +1485,7 @@ namespace  {
   struct InputFileEntry {
     const FileEntry *File;
     bool IsSystemFile;
+    bool IsTransient;
     bool BufferOverridden;
   };
 }
@@ -1502,6 +1503,7 @@ void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
   IFAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 12)); // Size
   IFAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::VBR, 32)); // Modification time
   IFAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Overridden
+  IFAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Fixed, 1)); // Transient
   IFAbbrev->Add(BitCodeAbbrevOp(BitCodeAbbrevOp::Blob)); // File name
   unsigned IFAbbrevCode = Stream.EmitAbbrev(IFAbbrev);
 
@@ -1523,6 +1525,7 @@ void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
     InputFileEntry Entry;
     Entry.File = Cache->OrigEntry;
     Entry.IsSystemFile = Cache->IsSystemFile;
+    Entry.IsTransient = Cache->IsTransient;
     Entry.BufferOverridden = Cache->BufferOverridden;
     if (Cache->IsSystemFile)
       SortedFiles.push_back(Entry);
@@ -1552,8 +1555,12 @@ void ASTWriter::WriteInputFiles(SourceManager &SourceMgr,
     // Emit size/modification time for this file.
     // And whether this file was overridden.
     RecordData::value_type Record[] = {
-        INPUT_FILE, InputFileOffsets.size(), (uint64_t)Entry.File->getSize(),
-        (uint64_t)getTimestampForOutput(Entry.File), Entry.BufferOverridden};
+        INPUT_FILE,
+        InputFileOffsets.size(),
+        (uint64_t)Entry.File->getSize(),
+        (uint64_t)getTimestampForOutput(Entry.File),
+        Entry.BufferOverridden,
+        Entry.IsTransient};
 
     EmitRecordWithPath(IFAbbrevCode, Record, Entry.File->getName());
   }
@@ -1902,7 +1909,7 @@ void ASTWriter::WriteSourceManagerBlock(SourceManager &SourceMgr,
         
         Stream.EmitRecordWithAbbrev(SLocFileAbbrv, Record);
         
-        if (Content->BufferOverridden) {
+        if (Content->BufferOverridden || Content->IsTransient) {
           RecordData::value_type Record[] = {SM_SLOC_BUFFER_BLOB};
           const llvm::MemoryBuffer *Buffer
             = Content->getBuffer(PP.getDiagnostics(), PP.getSourceManager());