Use weak cell to embed map in CompareNil IC.

src/code-stubs-hydrogen.cc

 // Copyright 2012 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/v8.h"
 
 #include "src/bailout-reason.h"
 #include "src/code-stubs.h"
 #include "src/field-index.h"
 #include "src/hydrogen.h"
@@ skipping 1084 matching lines @@
 }
 
 
 template <>
 HValue* CodeStubGraphBuilder<CompareNilICStub>::BuildCodeInitializedStub() {
   Isolate* isolate = graph()->isolate();
   CompareNilICStub* stub = casted_stub();
   HIfContinuation continuation;
   Handle<Map> sentinel_map(isolate->heap()->meta_map());
   Type* type = stub->GetType(zone(), sentinel_map);
-  BuildCompareNil(GetParameter(0), type, &continuation);
+  BuildCompareNil(GetParameter(0), type, &continuation, kEmbedMapsViaWeakCells);
   IfBuilder if_nil(this, &continuation);
   if_nil.Then();
   if (continuation.IsFalseReachable()) {
     if_nil.Else();
     if_nil.Return(graph()->GetConstant0());
   }
   if_nil.End();
   return continuation.IsTrueReachable()
       ? graph()->GetConstant1()
       : graph()->GetConstantUndefined();
@@ skipping 1084 matching lines @@
   // megamorphic case is handled as part of the default stub.
   DCHECK(!FLAG_vector_ics);
 
   // Probe the stub cache.
   Add<HTailCallThroughMegamorphicCache>(receiver, name);
 
   // We never continue.
   return graph()->GetConstant0();
 }
 } }  // namespace v8::internal