Tidy up inference of '@objc' and 'dynamic' for accessors.

No functionality change.

Author: jrose-apple

lib/Sema/TypeCheckDecl.cpp

@@ -4777,21 +4777,18 @@ class DeclChecker : public DeclVisitor<DeclChecker> {
         // The only additional condition we need to check is if the var decl
         // had an @objc or @iboutlet property.
 
-        ValueDecl *prop = cast<ValueDecl>(FD->getAccessorStorageDecl());
+        AbstractStorageDecl *storage = FD->getAccessorStorageDecl();
         // Validate the subscript or property because it might not be type
         // checked yet.
-        if (isa<SubscriptDecl>(prop))
-          TC.validateDecl(prop);
-        else if (isa<VarDecl>(prop))
-          TC.validateDecl(prop);
+        TC.validateDecl(storage);
 
-        if (prop->getAttrs().hasAttribute<NonObjCAttr>())
+        if (storage->getAttrs().hasAttribute<NonObjCAttr>())
           isObjC = None;
-        else if (!isObjC && prop->isObjC())
+        else if (!isObjC && storage->isObjC())
           isObjC = ObjCReason::DoNotDiagnose;
 
-        // If the property is dynamic, propagate to this accessor.
-        if (isObjC && prop->isDynamic() && !FD->isDynamic())
+        // If the storage is dynamic, propagate to this accessor.
+        if (isObjC && storage->isDynamic() && !FD->isDynamic())
           FD->getAttrs().add(new (TC.Context) DynamicAttr(/*implicit*/ true));
       }