1 files changed, 20 insertions, 1 deletions
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 9899eaf6989..8e19c708f73 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -755,6 +755,12 @@ static bool readBit(unsigned &Bits) {
   return Value;
 }
 
+IdentID ASTIdentifierLookupTrait::ReadIdentifierID(const unsigned char *d) {
+  using namespace llvm::support;
+  unsigned RawID = endian::readNext<uint32_t, little, unaligned>(d);
+  return Reader.getGlobalIdentifierID(F, RawID >> 1);
+}
+
 IdentifierInfo *ASTIdentifierLookupTrait::ReadData(const internal_key_type& k,
                                                    const unsigned char* d,
                                                    unsigned DataLen) {
@@ -3455,7 +3461,20 @@ ASTReader::ASTReadResult ASTReader::ReadAST(const std::string &FileName,
       ASTIdentifierLookupTrait Trait(*this, F);
       auto KeyDataLen = Trait.ReadKeyDataLength(Data);
       auto Key = Trait.ReadKey(Data, KeyDataLen.first);
-      PP.getIdentifierTable().getOwn(Key).setOutOfDate(true);
+      auto &II = PP.getIdentifierTable().getOwn(Key);
+      II.setOutOfDate(true);
+
+      // Mark this identifier as being from an AST file so that we can track
+      // whether we need to serialize it.
+      if (!II.isFromAST()) {
+        II.setIsFromAST();
+        if (isInterestingIdentifier(*this, II, F.isModule()))
+          II.setChangedSinceDeserialization();
+      }
+
+      // Associate the ID with the identifier so that the writer can reuse it.
+      auto ID = Trait.ReadIdentifierID(Data + KeyDataLen.first);
+      SetIdentifierInfo(ID, &II);
     }
   }