Remove superfluous HInnerAllocatedObject in BuildEmitDeepCopy

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 10004 matching lines @@
 
   // Copy object elements if non-COW.
   HValue* object_elements = BuildEmitObjectHeader(boilerplate_object, target,
       data_target, object_offset, elements_offset, elements_size);
   if (object_elements != NULL) {
     BuildEmitElements(elements, original_elements, kind, object_elements,
         target, offset, data_target, data_offset);
   }
 
   // Copy in-object properties.
-  HValue* object_properties =
-      AddInstruction(new(zone) HInnerAllocatedObject(target, object_offset));
-  BuildEmitInObjectProperties(boilerplate_object, original_boilerplate_object,
-      object_properties, target, offset, data_target, data_offset);
+  Handle<DescriptorArray> descriptors(
+      boilerplate_object->map()->instance_descriptors());
+  int descriptor_count = boilerplate_object->map()->NumberOfOwnDescriptors();
+  bool has_field = false;
+  for (int i = 0; i < descriptor_count; i++) {
+    PropertyDetails details = descriptors->GetDetails(i);
+    if (details.type() != FIELD) continue;
+    has_field = true;
+  }

[Toon Verwaest, 2013/06/27 04:32:22]

Isn't there a utility function to test for this condition? If not, add one to
jsobject or map. Specifically to test for fields you can also look at the unused
property fields, inobject properties etc to check this condition in O(1).

[danno, 2013/06/27 13:55:51]

OK, I now use map()->NumberOfFields(). I'll leave it to you to optimize
NumberOfFields to use a O(1) algorithm :-)

+
+  if (has_field) {
+    HValue* object_properties =
+        AddInstruction(new(zone) HInnerAllocatedObject(target, object_offset));
+    BuildEmitInObjectProperties(boilerplate_object, original_boilerplate_object,
+        object_properties, target, offset, data_target, data_offset);
+  }
 
   // Create allocation site info.
   if (mode == TRACK_ALLOCATION_SITE &&
       boilerplate_object->map()->CanTrackAllocationSite()) {
     elements_offset += AllocationSiteInfo::kSize;
     *offset += AllocationSiteInfo::kSize;
     HInstruction* original_boilerplate = AddInstruction(new(zone) HConstant(
         original_boilerplate_object));
     BuildCreateAllocationSiteInfo(target, JSArray::kSize, original_boilerplate);
   }
@@ skipping 1515 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal