Replace instance type check for polymorphic array.length with map check

src/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 6548 matching lines @@
     HValue* object,
     SmallMapList* types,
     Handle<String> name) {
   if (!name->Equals(isolate()->heap()->length_string())) return false;
 
   for (int i = 0; i < types->length(); i++) {
     if (types->at(i)->instance_type() != JS_ARRAY_TYPE) return false;
   }
 
   AddInstruction(new(zone()) HCheckNonSmi(object));
+
   HInstruction* typecheck =
-    AddInstruction(HCheckInstanceType::NewIsJSArray(object, zone()));
+    AddInstruction(new(zone()) HCheckMaps(object, types, zone()));
   HInstruction* instr =
     HLoadNamedField::NewArrayLength(zone(), object, typecheck);
   instr->set_position(expr->position());
   ast_context()->ReturnInstruction(instr, expr->id());
   return true;
 }
 
 
 void HOptimizedGraphBuilder::HandlePolymorphicLoadNamedField(Property* expr,
     HValue* object,
@@ skipping 5085 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal