Introduce a PrototypeIterator template and use it all over the place

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"
 
@@ skipping 6739 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()));
-    JSObject* holder = JSObject::cast(map->prototype());
-    while (!holder->GetPrototype()->IsNull()) {
-      holder = JSObject::cast(holder->GetPrototype());
+    JSObject* holder = NULL;
+    for (PrototypeIterator<STORE_AS_POINTER, MAP_BASED_WALK, END_AT_NULL_VALUE>
+             iter(*prototype); !iter.IsAtEnd(); iter.Advance()) {
+      holder = JSObject::cast(iter.GetCurrent());
     }
 
     BuildCheckPrototypeMaps(prototype,
                             Handle<JSObject>(JSObject::cast(holder)));
   }
 
   LoadKeyedHoleMode load_mode = BuildKeyedHoleMode(map);
   return BuildUncheckedMonomorphicElementAccess(
       checked_object, key, val,
       map->instance_type() == JS_ARRAY_TYPE,
@@ skipping 457 matching lines @@
       Add<HConstant>(constant), handle(constant->map()));
   check->ClearDependsOnFlag(kElementsKind);
   return check;
 }
 
 
 HInstruction* HGraphBuilder::BuildCheckPrototypeMaps(Handle<JSObject> prototype,
                                                      Handle<JSObject> holder) {
   while (holder.is_null() || !prototype.is_identical_to(holder)) {
     BuildConstantMapCheck(prototype);
-    Object* next_prototype = prototype->GetPrototype();
+    Object* next_prototype = SAFE_GET_PROTOTYPE_FAST(*prototype);
     if (next_prototype->IsNull()) return NULL;
     CHECK(next_prototype->IsJSObject());
     prototype = handle(JSObject::cast(next_prototype));
   }
   return BuildConstantMapCheck(prototype);
 }
 
 
 void HOptimizedGraphBuilder::AddCheckPrototypeMaps(Handle<JSObject> holder,
                                                    Handle<Map> receiver_map) {
@@ skipping 5098 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal