3 files changed, 40 insertions, 17 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);
     }
   }
 
diff --git a/clang/lib/Serialization/ASTReaderInternals.h b/clang/lib/Serialization/ASTReaderInternals.h
index 701cf7300f6..47640f6c47b 100644
--- a/clang/lib/Serialization/ASTReaderInternals.h
+++ b/clang/lib/Serialization/ASTReaderInternals.h
@@ -137,6 +137,8 @@ public:
                      const unsigned char* d,
                      unsigned DataLen);
   
+  IdentID ReadIdentifierID(const unsigned char *d);
+
   ASTReader &getReader() const { return Reader; }
 };
   
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index d7803d166ee..678258eb44f 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -4273,22 +4273,24 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
   }
 
   // Make sure all decls associated with an identifier are registered for
-  // serialization.
-  llvm::SmallVector<const IdentifierInfo*, 256> IIs;
-  for (IdentifierTable::iterator ID = PP.getIdentifierTable().begin(),
-                              IDEnd = PP.getIdentifierTable().end();
-       ID != IDEnd; ++ID) {
-    const IdentifierInfo *II = ID->second;
-    if (!Chain || !II->isFromAST() || II->hasChangedSinceDeserialization())
-      IIs.push_back(II);
-  }
-  // Sort the identifiers to visit based on their name.
-  std::sort(IIs.begin(), IIs.end(), llvm::less_ptr<IdentifierInfo>());
-  for (const IdentifierInfo *II : IIs) {
-    for (IdentifierResolver::iterator D = SemaRef.IdResolver.begin(II),
-                                   DEnd = SemaRef.IdResolver.end();
-         D != DEnd; ++D) {
-      GetDeclRef(*D);
+  // serialization, if we're storing decls with identifiers.
+  if (!WritingModule || !getLangOpts().CPlusPlus) {
+    llvm::SmallVector<const IdentifierInfo*, 256> IIs;
+    for (IdentifierTable::iterator ID = PP.getIdentifierTable().begin(),
+                                IDEnd = PP.getIdentifierTable().end();
+         ID != IDEnd; ++ID) {
+      const IdentifierInfo *II = ID->second;
+      if (!Chain || !II->isFromAST() || II->hasChangedSinceDeserialization())
+        IIs.push_back(II);
+    }
+    // Sort the identifiers to visit based on their name.
+    std::sort(IIs.begin(), IIs.end(), llvm::less_ptr<IdentifierInfo>());
+    for (const IdentifierInfo *II : IIs) {
+      for (IdentifierResolver::iterator D = SemaRef.IdResolver.begin(II),
+                                     DEnd = SemaRef.IdResolver.end();
+           D != DEnd; ++D) {
+        GetDeclRef(*D);
+      }
     }
   }