3 files changed, 15 insertions, 37 deletions

diff --git a/clang/lib/Serialization/ASTCommon.cpp b/clang/lib/Serialization/ASTCommon.cpp
index 04425acb4c5..85c574c2021 100644
--- a/clang/lib/Serialization/ASTCommon.cpp
+++ b/clang/lib/Serialization/ASTCommon.cpp
@@ -94,6 +94,7 @@ serialization::getDefinitiveDeclContext(const DeclContext *DC) {
   switch (DC->getDeclKind()) {
   // These entities may have multiple definitions.
   case Decl::TranslationUnit:
+  case Decl::ExternCContext:
   case Decl::Namespace:
   case Decl::LinkageSpec:
     return nullptr;
@@ -149,7 +150,11 @@ serialization::getDefinitiveDeclContext(const DeclContext *DC) {
 
 bool serialization::isRedeclarableDeclKind(unsigned Kind) {
   switch (static_cast<Decl::Kind>(Kind)) {
-  case Decl::TranslationUnit: // Special case of a "merged" declaration.
+  case Decl::TranslationUnit:
+  case Decl::ExternCContext:
+    // Special case of a "merged" declaration.
+    return true;
+
   case Decl::Namespace:
   case Decl::NamespaceAlias:
   case Decl::Typedef:
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index d3721bbe342..7e3a779b076 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -2892,11 +2892,6 @@ ASTReader::ReadASTBlock(ModuleFile &F, unsigned ClientLoadCapabilities) {
       }
       break;
 
-    case LOCALLY_SCOPED_EXTERN_C_DECLS:
-      for (unsigned I = 0, N = Record.size(); I != N; ++I)
-        LocallyScopedExternCDecls.push_back(getGlobalDeclID(F, Record[I]));
-      break;
-
     case SELECTOR_OFFSETS: {
       F.SelectorOffsets = (const uint32_t *)Blob.data();
       F.LocalNumSelectors = Record[0];
@@ -6284,6 +6279,9 @@ static Decl *getPredefinedDecl(ASTContext &Context, PredefinedDeclIDs ID) {
 
   case PREDEF_DECL_BUILTIN_VA_LIST_ID:
     return Context.getBuiltinVaListDecl();
+
+  case PREDEF_DECL_EXTERN_C_CONTEXT_ID:
+    return Context.getExternCContextDecl();
   }
   llvm_unreachable("PredefinedDeclIDs unknown enum value");
 }
@@ -7326,17 +7324,6 @@ void ASTReader::ReadUnusedLocalTypedefNameCandidates(
   UnusedLocalTypedefNameCandidates.clear();
 }
 
-void 
-ASTReader::ReadLocallyScopedExternCDecls(SmallVectorImpl<NamedDecl *> &Decls) {
-  for (unsigned I = 0, N = LocallyScopedExternCDecls.size(); I != N; ++I) {
-    NamedDecl *D
-      = dyn_cast_or_null<NamedDecl>(GetDecl(LocallyScopedExternCDecls[I]));
-    if (D)
-      Decls.push_back(D);
-  }
-  LocallyScopedExternCDecls.clear();
-}
-
 void ASTReader::ReadReferencedSelectors(
        SmallVectorImpl<std::pair<Selector, SourceLocation> > &Sels) {
   if (ReferencedSelectorsData.empty())
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index 19c7a966253..f92848ad21f 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -892,7 +892,6 @@ void ASTWriter::WriteBlockInfoBlock() {
   RECORD(STATISTICS);
   RECORD(TENTATIVE_DEFINITIONS);
   RECORD(UNUSED_FILESCOPED_DECLS);
-  RECORD(LOCALLY_SCOPED_EXTERN_C_DECLS);
   RECORD(SELECTOR_OFFSETS);
   RECORD(METHOD_POOL);
   RECORD(PP_COUNTER_VALUE);
@@ -4231,6 +4230,8 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
     DeclIDs[Context.ObjCInstanceTypeDecl] = PREDEF_DECL_OBJC_INSTANCETYPE_ID;
   if (Context.BuiltinVaListDecl)
     DeclIDs[Context.getBuiltinVaListDecl()] = PREDEF_DECL_BUILTIN_VA_LIST_ID;
+  if (Context.ExternCContext)
+    DeclIDs[Context.ExternCContext] = PREDEF_DECL_EXTERN_C_CONTEXT_ID;
 
   if (!Chain) {
     // Make sure that we emit IdentifierInfos (and any attached
@@ -4289,20 +4290,6 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
     }
   }
 
-  // Build a record containing all of the locally-scoped extern "C"
-  // declarations in this header file. Generally, this record will be
-  // empty.
-  RecordData LocallyScopedExternCDecls;
-  // FIXME: This is filling in the AST file in densemap order which is
-  // nondeterminstic!
-  for (llvm::DenseMap<DeclarationName, NamedDecl *>::iterator
-         TD = SemaRef.LocallyScopedExternCDecls.begin(),
-         TDEnd = SemaRef.LocallyScopedExternCDecls.end();
-       TD != TDEnd; ++TD) {
-    if (!TD->second->isFromASTFile())
-      AddDeclRef(TD->second, LocallyScopedExternCDecls);
-  }
-  
   // Build a record containing all of the ext_vector declarations.
   RecordData ExtVectorDecls;
   AddLazyVectorDecls(*this, SemaRef.ExtVectorDecls, ExtVectorDecls);
@@ -4405,6 +4392,10 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
   Abv->Add(llvm::BitCodeAbbrevOp(llvm::BitCodeAbbrevOp::Blob));
   UpdateVisibleAbbrev = Stream.EmitAbbrev(Abv);
   WriteDeclContextVisibleUpdate(TU);
+
+  // If we have any extern "C" names, write out a visible update for them.
+  if (Context.ExternCContext)
+    WriteDeclContextVisibleUpdate(Context.ExternCContext);
   
   // If the translation unit has an anonymous namespace, and we don't already
   // have an update block for it, write it as an update block.
@@ -4589,11 +4580,6 @@ void ASTWriter::WriteASTCore(Sema &SemaRef,
     Stream.EmitRecord(WEAK_UNDECLARED_IDENTIFIERS,
                       WeakUndeclaredIdentifiers);
 
-  // Write the record containing locally-scoped extern "C" definitions.
-  if (!LocallyScopedExternCDecls.empty())
-    Stream.EmitRecord(LOCALLY_SCOPED_EXTERN_C_DECLS,
-                      LocallyScopedExternCDecls);
-
   // Write the record containing ext_vector type names.
   if (!ExtVectorDecls.empty())
     Stream.EmitRecord(EXT_VECTOR_DECLS, ExtVectorDecls);