Stores to external references don't need write barriers.

src/code-stubs-hydrogen.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 441 matching lines @@
 }
 
 
 Handle<Code> FastCloneShallowObjectStub::GenerateCode() {
   return DoGenerateCode(this);
 }
 
 
 template <>
 HValue* CodeStubGraphBuilder<CreateAllocationSiteStub>::BuildCodeStub() {
-  Zone* zone = this->zone();
-
-  HValue* size = AddInstruction(new(zone) HConstant(AllocationSite::kSize));
-  HInstruction* object = AddInstruction(new(zone)
-      HAllocate(context(), size, HType::JSObject(), true));
+  HValue* size = Add<HConstant>(AllocationSite::kSize);
+  HInstruction* object = Add<HAllocate>(
+      context(), size, HType::JSObject(), true);
 
   // Store the map
   Handle<Map> allocation_site_map(isolate()->heap()->allocation_site_map(),
                                   isolate());
   AddStoreMapConstant(object, allocation_site_map);
 
   // Store the payload (smi elements kind)
-  HValue* initial_elements_kind = AddInstruction(new(zone) HConstant(
-      GetInitialFastElementsKind()));
+  HValue* initial_elements_kind = Add<HConstant>(GetInitialFastElementsKind());
   Add<HStoreNamedField>(object,
                         HObjectAccess::ForAllocationSiteTransitionInfo(),
                         initial_elements_kind);
 
   // Link the object to the allocation site list
   HValue* site_list = Add<HConstant>(
       ExternalReference::allocation_sites_list_address(isolate()));
   HValue* site = AddLoad(site_list, HObjectAccess::ForAllocationSiteList());
   HStoreNamedField* store =
       AddStore(object, HObjectAccess::ForAllocationSiteWeakNext(), site);
@@ skipping 465 matching lines @@
   return value;
 }
 
 
 Handle<Code> ElementsTransitionAndStoreStub::GenerateCode() {
   return DoGenerateCode(this);
 }
 
 
 } }  // namespace v8::internal