3 files changed, 46 insertions, 1 deletions
diff --git a/lib/Serialization/ASTCommon.h b/lib/Serialization/ASTCommon.h
index a0e2ecd8aa..36958c7500 100644
--- a/lib/Serialization/ASTCommon.h
+++ b/lib/Serialization/ASTCommon.h
@@ -20,6 +20,10 @@ namespace clang {
 
 namespace serialization {
 
+enum DeclUpdateKind {
+  UPD_CXX_SET_DEFINITIONDATA
+};
+
 TypeIdx TypeIdxFromBuiltin(const BuiltinType *BT);
 
 template <typename IdxForTypeTy>
diff --git a/lib/Serialization/ASTReaderDecl.cpp b/lib/Serialization/ASTReaderDecl.cpp
index 45d729a2fc..f4568a7e70 100644
--- a/lib/Serialization/ASTReaderDecl.cpp
+++ b/lib/Serialization/ASTReaderDecl.cpp
@@ -1588,5 +1588,17 @@ Decl *ASTReader::ReadDeclRecord(unsigned Index, DeclID ID) {
 }
 
 void ASTDeclReader::UpdateDecl(Decl *D, const RecordData &Record) {
-  // No update is tracked yet.
+  unsigned Idx = 0;
+  while (Idx < Record.size()) {
+    switch ((DeclUpdateKind)Record[Idx++]) {
+    case UPD_CXX_SET_DEFINITIONDATA: {
+      CXXRecordDecl *RD = cast<CXXRecordDecl>(D);
+      CXXRecordDecl *
+          DefinitionDecl = cast<CXXRecordDecl>(Reader.GetDecl(Record[Idx++]));
+      assert(!RD->DefinitionData && "DefinitionData is already set!");
+      InitializeCXXDefinitionData(RD, DefinitionDecl, Record, Idx);
+      break;
+    }
+    }
+  }
 }
diff --git a/lib/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index c6df2dd95d..436525f199 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -3297,3 +3297,32 @@ void ASTWriter::MacroDefinitionRead(serialization::MacroID ID,
                                     MacroDefinition *MD) {
   MacroDefinitions[MD] = ID;
 }
+
+void ASTWriter::CompletedTagDefinition(const TagDecl *D) {
+  assert(D->isDefinition());
+  if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(D)) {
+    // We are interested when a PCH decl is modified.
+    if (RD->getPCHLevel() > 0) {
+      // A forward reference was mutated into a definition. Rewrite it.
+      // FIXME: This happens during template instantiation, should we
+      // have created a new definition decl instead ?
+      DeclsToRewrite.insert(RD);
+    }
+
+    for (CXXRecordDecl::redecl_iterator
+           I = RD->redecls_begin(), E = RD->redecls_end(); I != E; ++I) {
+      CXXRecordDecl *Redecl = cast<CXXRecordDecl>(*I);
+      if (Redecl == RD)
+        continue;
+
+      // We are interested when a PCH decl is modified.
+      if (Redecl->getPCHLevel() > 0) {
+        UpdateRecord &Record = DeclUpdates[Redecl];
+        Record.push_back(UPD_CXX_SET_DEFINITIONDATA);
+        assert(Redecl->DefinitionData);
+        assert(Redecl->DefinitionData->Definition == D);
+        AddDeclRef(D, Record); // the DefinitionDecl
+      }
+    }
+  }
+}