1 files changed, 16 insertions, 0 deletions
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 0681e3975d2..e39e5bb0222 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -51,6 +51,7 @@
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/OnDiskHashTable.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
 #include <algorithm>
 #include <cstdio>
 #include <string.h>
@@ -862,6 +863,7 @@ void ASTWriter::WriteBlockInfoBlock() {
   // Control Block.
   BLOCK(CONTROL_BLOCK);
   RECORD(METADATA);
+  RECORD(SIGNATURE);
   RECORD(MODULE_NAME);
   RECORD(MODULE_MAP_FILE);
   RECORD(IMPORTS);
@@ -1092,6 +1094,14 @@ adjustFilenameForRelocatablePCH(const char *Filename, StringRef isysroot) {
   return Filename + Pos;
 }
 
+static ASTFileSignature getSignature() {
+  while (1) {
+    if (ASTFileSignature S = llvm::sys::Process::GetRandomNumber())
+      return S;
+    // Rely on GetRandomNumber to eventually return non-zero...
+  }
+}
+
 /// \brief Write the control block.
 void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
                                   StringRef isysroot,
@@ -1121,6 +1131,11 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
   Stream.EmitRecordWithBlob(MetadataAbbrevCode, Record,
                             getClangFullRepositoryVersion());
 
+  // Signature
+  Record.clear();
+  Record.push_back(getSignature());
+  Stream.EmitRecord(SIGNATURE, Record);
+
   // Module name
   if (WritingModule) {
     BitCodeAbbrev *Abbrev = new BitCodeAbbrev();
@@ -1173,6 +1188,7 @@ void ASTWriter::WriteControlBlock(Preprocessor &PP, ASTContext &Context,
       AddSourceLocation((*M)->ImportLoc, Record);
       Record.push_back((*M)->File->getSize());
       Record.push_back((*M)->File->getModificationTime());
+      Record.push_back((*M)->Signature);
       const std::string &FileName = (*M)->FileName;
       Record.push_back(FileName.size());
       Record.append(FileName.begin(), FileName.end());