Pretenure code generation corner case with new space COW arrays.

src/hydrogen.cc

 // Copyright 2013 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 9755 matching lines @@
 
   HInstruction* object = Add<HAllocate>(object_size_constant, type,
       pretenure_flag, instance_type, site_context->current());
 
   BuildEmitObjectHeader(boilerplate_object, object);
 
   Handle<FixedArrayBase> elements(boilerplate_object->elements());
   int elements_size = (elements->length() > 0 &&
       elements->map() != isolate()->heap()->fixed_cow_array_map()) ?
           elements->Size() : 0;
 

[Hannes Payer (out of office), 2014/03/17 09:37:18]

This method needs more comments... please explain what is going on here.

[mvstanton, 2014/03/17 12:25:28]

Done.

+  if (pretenure_flag == TENURED &&
+      elements->map() == isolate()->heap()->fixed_cow_array_map() &&
+      isolate()->heap()->InNewSpace(*elements)) {
+    elements = Handle<FixedArrayBase>(
+        isolate()->factory()->CopyAndTenureFixedCOWArray(
+            Handle<FixedArray>::cast(elements)));
+    boilerplate_object->set_elements(*elements);
+  }
+
   HInstruction* object_elements = NULL;
   if (elements_size > 0) {
     HValue* object_elements_size = Add<HConstant>(elements_size);
     if (boilerplate_object->HasFastDoubleElements()) {
       // Allocation folding will not be able to fold |object| and
       // |object_elements| together if they are pre-tenured.
       if (pretenure_flag == TENURED) {
         HConstant* empty_fixed_array = Add<HConstant>(
             isolate()->factory()->empty_fixed_array());
         Add<HStoreNamedField>(object, HObjectAccess::ForElementsPointer(),
@@ skipping 1486 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal