Simplify prototype chain walk in hydrogen

src/hydrogen.cc

 // Copyright 2013 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/hydrogen.h"
 
 #include <algorithm>
 
 #include "src/v8.h"
 #include "src/allocation-site-scopes.h"
@@ skipping 6540 matching lines @@
   HCheckMaps* checked_object = Add<HCheckMaps>(object, map, dependency);
   if (dependency) {
     checked_object->ClearDependsOnFlag(kElementsKind);
   }
 
   if (access_type == STORE && map->prototype()->IsJSObject()) {
     // monomorphic stores need a prototype chain check because shape
     // changes could allow callbacks on elements in the chain that
     // aren't compatible with monomorphic keyed stores.
     Handle<JSObject> prototype(JSObject::cast(map->prototype()));
-    Object* holder = map->prototype();
-    while (holder->GetPrototype(isolate())->IsJSObject()) {
-      holder = holder->GetPrototype(isolate());
+    JSObject* holder = JSObject::cast(map->prototype());
+    while (!holder->GetPrototype()->IsNull()) {
+      holder = JSObject::cast(holder->GetPrototype());
     }
-    ASSERT(holder->GetPrototype(isolate())->IsNull());
 
     BuildCheckPrototypeMaps(prototype,
                             Handle<JSObject>(JSObject::cast(holder)));
   }
 
   LoadKeyedHoleMode load_mode = BuildKeyedHoleMode(map);
   return BuildUncheckedMonomorphicElementAccess(
       checked_object, key, val,
       map->instance_type() == JS_ARRAY_TYPE,
       map->elements_kind(), access_type,
@@ skipping 5564 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal