Avoid double initialization of arrays.

src/builtins.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 556 matching lines @@
 
     int new_length = len + to_add;
 
     if (new_length > elms->length()) {
       // New backing storage is needed.
       int capacity = new_length + (new_length >> 1) + 16;
       FixedArray* new_elms;
       MaybeObject* maybe_obj = heap->AllocateUninitializedFixedArray(capacity);
       if (!maybe_obj->To(&new_elms)) return maybe_obj;
 
-      if (len > 0) {
-        ElementsAccessor* accessor = array->GetElementsAccessor();
-        MaybeObject* maybe_failure =
-            accessor->CopyElements(NULL, 0, new_elms, kind, 0, len, elms_obj);
-        ASSERT(!maybe_failure->IsFailure());
-        USE(maybe_failure);
-      }
-      FillWithHoles(heap, new_elms, new_length, capacity);
+      ElementsAccessor* accessor = array->GetElementsAccessor();
+      MaybeObject* maybe_failure =
+          accessor->CopyElements(

[Michael Starzinger, 2012/11/27 11:53:56]

Move the accessor->CopyElements into the first line, this will get rid of one
indentation level.

[Toon Verwaest, 2012/11/27 11:59:30]

Done.

+              NULL, 0, new_elms, kind, 0,
+              ElementsAccessor::kCopyToEndAndInitializeToHole, elms_obj);
+      ASSERT(!maybe_failure->IsFailure());
+      USE(maybe_failure);
 
       elms = new_elms;
     }
 
     // Add the provided values.
     AssertNoAllocation no_gc;
     WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
     for (int index = 0; index < to_add; index++) {
       elms->set(index + len, args[index + 1], mode);
     }
@@ skipping 21 matching lines @@
 
     FixedDoubleArray* new_elms;
 
     if (new_length > elms_len) {
       // New backing storage is needed.
       int capacity = new_length + (new_length >> 1) + 16;
       MaybeObject* maybe_obj =
           heap->AllocateUninitializedFixedDoubleArray(capacity);
       if (!maybe_obj->To(&new_elms)) return maybe_obj;
 
-      if (len > 0) {
-        ElementsAccessor* accessor = array->GetElementsAccessor();
-        MaybeObject* maybe_failure =
-            accessor->CopyElements(NULL, 0, new_elms, kind, 0, len, elms_obj);
-        ASSERT(!maybe_failure->IsFailure());
-        USE(maybe_failure);
-      }
-
-      FillWithHoles(new_elms, len + to_add, new_elms->length());
+      ElementsAccessor* accessor = array->GetElementsAccessor();
+      MaybeObject* maybe_failure =
+          accessor->CopyElements(

[Michael Starzinger, 2012/11/27 11:53:56]

Likewise.

[Toon Verwaest, 2012/11/27 11:59:30]

Done.

+              NULL, 0, new_elms, kind, 0,
+              ElementsAccessor::kCopyToEndAndInitializeToHole, elms_obj);
+      ASSERT(!maybe_failure->IsFailure());
+      USE(maybe_failure);
     } else {
       // to_add is > 0 and new_length <= elms_len, so elms_obj cannot be the
       // empty_fixed_array.
       new_elms = FixedDoubleArray::cast(elms_obj);
     }
 
     // Add the provided values.
     AssertNoAllocation no_gc;
     int index;
     for (index = 0; index < to_add; index++) {
@@ skipping 135 matching lines @@
                                       DONT_ALLOW_DOUBLE_ELEMENTS);
   if (maybe_object->IsFailure()) return maybe_object;
 
   if (new_length > elms->length()) {
     // New backing storage is needed.
     int capacity = new_length + (new_length >> 1) + 16;
     FixedArray* new_elms;
     MaybeObject* maybe_elms = heap->AllocateUninitializedFixedArray(capacity);
     if (!maybe_elms->To(&new_elms)) return maybe_elms;
 
-    if (len > 0) {
-      ElementsKind kind = array->GetElementsKind();
-      ElementsAccessor* accessor = array->GetElementsAccessor();
-      MaybeObject* maybe_failure =
-          accessor->CopyElements(NULL, 0, new_elms, kind, to_add, len, elms);
-      ASSERT(!maybe_failure->IsFailure());
-      USE(maybe_failure);
-    }
+    ElementsKind kind = array->GetElementsKind();
+    ElementsAccessor* accessor = array->GetElementsAccessor();
+    MaybeObject* maybe_failure =
+        accessor->CopyElements(

[Michael Starzinger, 2012/11/27 11:53:56]

Likewise.

[Toon Verwaest, 2012/11/27 11:59:30]

Done.

+            NULL, 0, new_elms, kind, to_add,
+            ElementsAccessor::kCopyToEndAndInitializeToHole, elms);
+    ASSERT(!maybe_failure->IsFailure());
+    USE(maybe_failure);
 
-    FillWithHoles(heap, new_elms, new_length, capacity);
     elms = new_elms;
     array->set_elements(elms);
   } else {
     AssertNoAllocation no_gc;
     MoveElements(heap, &no_gc, elms, to_add, elms, 0, len);
   }
 
   // Add the provided values.
   AssertNoAllocation no_gc;
   WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
@@ skipping 299 matching lines @@
 
       ElementsKind kind = array->GetElementsKind();
       ElementsAccessor* accessor = array->GetElementsAccessor();
       if (actual_start > 0) {
         // Copy the part before actual_start as is.
         MaybeObject* maybe_failure = accessor->CopyElements(
             NULL, 0, new_elms, kind, 0, actual_start, elms);
         ASSERT(!maybe_failure->IsFailure());
         USE(maybe_failure);
       }
-      const int to_copy = len - actual_delete_count - actual_start;
-      if (to_copy > 0) {
-        MaybeObject* maybe_failure = accessor->CopyElements(
-            NULL, actual_start + actual_delete_count, new_elms, kind,
-            actual_start + item_count, to_copy, elms);
-        ASSERT(!maybe_failure->IsFailure());
-        USE(maybe_failure);
-      }
-
-      FillWithHoles(heap, new_elms, new_length, capacity);
+      MaybeObject* maybe_failure = accessor->CopyElements(
+          NULL, actual_start + actual_delete_count, new_elms, kind,
+          actual_start + item_count,
+          ElementsAccessor::kCopyToEndAndInitializeToHole, elms);
+      ASSERT(!maybe_failure->IsFailure());
+      USE(maybe_failure);
 
       elms_obj = new_elms;
       elms_changed = true;
     } else {
       AssertNoAllocation no_gc;
       MoveElements(heap, &no_gc,
                    elms, actual_start + item_count,
                    elms, actual_start + actual_delete_count,
                    (len - actual_delete_count - actual_start));
     }
@@ skipping 807 matching lines @@
   return Handle<Code>(code_address);                        \
 }
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 } }  // namespace v8::internal