More objc gc stuff. Read/Write barriers for local static/extern,
diagnostics on use of __weak attribute on fields,
Early support for read/write barriers for objc fields.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59682 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 4bf55dd..57d1cc7 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -555,8 +555,11 @@
   
   
   ObjCGCAttr::GCAttrTypes type;
-  if (Attr.getParameterName()->isName("weak"))
+  if (Attr.getParameterName()->isName("weak")) {
+    if (isa<FieldDecl>(d))
+      S.Diag(Attr.getLoc(), diag::warn_attribute_weak_on_field);
     type = ObjCGCAttr::Weak;
+  }
   else if (Attr.getParameterName()->isName("strong"))
     type = ObjCGCAttr::Strong;
   else {