[builtins] Fix Generate_AtomicsStore.

src/builtins/builtins-sharedarraybuffer.cc

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/builtins/builtins.h"
 #include "src/builtins/builtins-utils.h"
 
 #include "src/code-factory.h"
 
 namespace v8 {
@@ skipping 231 matching lines @@
   };
   a->Switch(instance_type, &other, case_values, case_labels,
             arraysize(case_labels));
 
   a->Bind(&u8);
   a->AtomicStore(MachineRepresentation::kWord8, backing_store, index_word,
                  value_word32);
   a->Return(value_integer);
 
   a->Bind(&u16);
-  a->SmiTag(a->AtomicStore(MachineRepresentation::kWord16, backing_store,
-                           a->WordShl(index_word, 1), value_word32));
+  a->AtomicStore(MachineRepresentation::kWord16, backing_store,
+                 a->WordShl(index_word, 1), value_word32);
   a->Return(value_integer);
 
   a->Bind(&u32);
   a->AtomicStore(MachineRepresentation::kWord32, backing_store,
                  a->WordShl(index_word, 2), value_word32);
   a->Return(value_integer);
 
   // This shouldn't happen, we've already validated the type.
   a->Bind(&other);
   a->Return(a->Int32Constant(0));
 }
 
 }  // namespace internal
 }  // namespace v8