3 files changed, 40 insertions, 1 deletions
diff --git a/clang/lib/Sema/AttributeList.cpp b/clang/lib/Sema/AttributeList.cpp
index afc23e9be20..5a8330bbfd7 100644
--- a/clang/lib/Sema/AttributeList.cpp
+++ b/clang/lib/Sema/AttributeList.cpp
@@ -107,6 +107,7 @@ AttributeList::Kind AttributeList::getKind(const IdentifierInfo *Name) {
   return llvm::StringSwitch<AttributeList::Kind>(AttrName)
     .Case("weak", AT_weak)
     .Case("weakref", AT_weakref)
+    .Case("objc_arc_weak_reference_unavailable", AT_arc_weakref_unavailable)
     .Case("pure", AT_pure)
     .Case("mode", AT_mode)
     .Case("used", AT_used)
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 103976bc12f..adef528b0a4 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -1091,6 +1091,18 @@ static void handleUnavailableAttr(Sema &S, Decl *D, const AttributeList &Attr) {
   D->addAttr(::new (S.Context) UnavailableAttr(Attr.getLoc(), S.Context, Str));
 }
 
+static void handleArcWeakrefUnavailableAttr(Sema &S, Decl *D, 
+                                            const AttributeList &Attr) {
+  unsigned NumArgs = Attr.getNumArgs();
+  if (NumArgs > 0) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_too_many_arguments) << 0;
+    return;
+  }
+  
+  D->addAttr(::new (S.Context) ArcWeakrefUnavailableAttr(
+                                          Attr.getLoc(), S.Context));
+}
+
 static void handleAvailabilityAttr(Sema &S, Decl *D,
                                    const AttributeList &Attr) {
   IdentifierInfo *Platform = Attr.getParameterName();
@@ -3011,6 +3023,9 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_MsStruct:    handleMsStructAttr    (S, D, Attr); break;
   case AttributeList::AT_section:     handleSectionAttr     (S, D, Attr); break;
   case AttributeList::AT_unavailable: handleUnavailableAttr (S, D, Attr); break;
+  case AttributeList::AT_arc_weakref_unavailable: 
+    handleArcWeakrefUnavailableAttr (S, D, Attr); 
+    break;
   case AttributeList::AT_unused:      handleUnusedAttr      (S, D, Attr); break;
   case AttributeList::AT_used:        handleUsedAttr        (S, D, Attr); break;
   case AttributeList::AT_visibility:  handleVisibilityAttr  (S, D, Attr); break;
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 14184220064..ae1ccf9886d 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -3207,7 +3207,30 @@ static bool handleObjCOwnershipTypeAttr(TypeProcessingState &state,
     attr.setInvalid();
     return true;
   }
-
+    
+  // Forbid __weak for class objects marked as 
+  // objc_arc_weak_reference_unavailable
+  if (lifetime == Qualifiers::OCL_Weak) {
+    QualType T = type;
+    if (T->isReferenceType()) {
+      T = T->getAs<ReferenceType>()->getPointeeType();
+    }
+    while (const PointerType *ptr = T->getAs<PointerType>())
+      T = ptr->getPointeeType();
+    if (const ObjCObjectPointerType *ObjT = T->getAs<ObjCObjectPointerType>()) {
+      ObjCInterfaceDecl *Class = ObjT->getInterfaceDecl();
+      while (Class) {
+        if (Class->hasAttr<ArcWeakrefUnavailableAttr>()) {
+          S.Diag(attr.getLoc(), diag::err_arc_unsupported_weak_class);
+          S.Diag(ObjT->getInterfaceDecl()->getLocation(), 
+                 diag::note_class_declared);
+          break;
+        }
+        Class = Class->getSuperClass();
+      }
+    }
+  }
+  
   return true;
 }