Use the initial map of the Object function for empty object literals

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 10983 matching lines @@
   }
   BuildInitElementsInObjectHeader(boilerplate_object, object, object_elements);
 
   // Copy object elements if non-COW.
   if (object_elements != NULL) {
     BuildEmitElements(boilerplate_object, elements, object_elements,
                       site_context);
   }
 
   // Copy in-object properties.
-  if (boilerplate_object->map()->NumberOfFields() != 0) {
+  if (boilerplate_object->map()->NumberOfFields() != 0 ||
+      boilerplate_object->map()->unused_property_fields() > 0) {
     BuildEmitInObjectProperties(boilerplate_object, object, site_context,
                                 pretenure_flag);
   }
   return object;
 }
 
 
 void HOptimizedGraphBuilder::BuildEmitObjectHeader(
     Handle<JSObject> boilerplate_object,
     HInstruction* object) {
@@ skipping 193 matching lines @@
 void HOptimizedGraphBuilder::VisitThisFunction(ThisFunction* expr) {
   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   HInstruction* instr = BuildThisFunction();
   return ast_context()->ReturnInstruction(instr, expr->id());
 }
 
 
 void HOptimizedGraphBuilder::VisitSuperReference(SuperReference* expr) {
   DCHECK(!HasStackOverflow());

[Toon Verwaest, 2014/09/19 12:27:57]

Unrelated to this CL, just rebased.

   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   return Bailout(kSuperReference);
 }
 
 
 void HOptimizedGraphBuilder::VisitDeclarations(
     ZoneList<Declaration*>* declarations) {
   DCHECK(globals_.is_empty());
   AstVisitor::VisitDeclarations(declarations);
@@ skipping 1289 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal