[heap] Add optimized RecordWrites

src/elements.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/elements.h"
 
 #include "src/arguments.h"
 #include "src/conversions.h"
 #include "src/factory.h"
 #include "src/isolate-inl.h"
@@ skipping 993 matching lines @@
         for (uint32_t i = 0; i < nof_indices; i++) {
           Handle<Object> index_string = isolate->factory()->Uint32ToString(
                   combined_keys->get(i)->Number());
           combined_keys->set(i, *index_string);
         }
       } else if (!(object->IsJSArray() &&
                    JSArray::cast(*object)->length()->ToArrayLength(
                        &array_length) &&
                    array_length <= Smi::kMaxValue)) {
         // Since we use std::sort above, the GC will no longer know where the
         // HeapNumbers are, hence we have to write them again.

[Hannes Payer (out of office), 2016/04/01 11:34:39]

Update this comment.

         // For Arrays with valid Smi length, we are sure to have no HeapNumber
         // indices and thus we can skip this step.
-        for (uint32_t i = 0; i < nof_indices; i++) {
-          Object* index = combined_keys->get(i);
-          combined_keys->set(i, index);
-        }
+        FIXED_ARRAY_WRITE_BARRIER(isolate->heap(), *combined_keys, 0,
+                                  nof_indices);
       }
     }
 
     // Copy over the passed-in property keys.
     CopyObjectToObjectElements(*keys, FAST_ELEMENTS, 0, *combined_keys,
                                FAST_ELEMENTS, nof_indices, nof_property_keys);
 
     if (IsHoleyElementsKind(kind())) {
       // Shrink combined_keys to the final size.
       int final_size = nof_indices + nof_property_keys;
@@ skipping 1998 matching lines @@
     insertion_index += len;
   }
 
   DCHECK_EQ(insertion_index, result_len);
   return result_array;
 }
 
 ElementsAccessor** ElementsAccessor::elements_accessors_ = NULL;
 }  // namespace internal
 }  // namespace v8