[runtime] enable fast key accumulator by default

src/elements.cc

Index: src/elements.cc
diff --git a/src/elements.cc b/src/elements.cc
index 3cf8378162844a1fc00525e3ccacdb6f47406ac5..7f386125b75b1fe2a1217088dbf4d09ce3d3e788 100644
--- a/src/elements.cc
+++ b/src/elements.cc
@@ -982,19 +982,22 @@ class ElementsAccessorBase : public ElementsAccessor {
     Isolate* isolate = object->GetIsolate();
     uint32_t nof_property_keys = keys->length();
     uint32_t initial_list_length =
-        Subclass::GetCapacityImpl(*object, *backing_store);
+        Subclass::GetMaxNumberOfEntries(*object, *backing_store);
     initial_list_length += nof_property_keys;
 
+    bool needs_sorting =
+        IsDictionaryElementsKind(kind()) || IsSloppyArgumentsElements(kind());
+
     // Collect the element indices into a new list.
     uint32_t nof_indices = 0;
     Handle<FixedArray> combined_keys =
         isolate->factory()->NewFixedArray(initial_list_length);
     combined_keys = Subclass::DirectCollectElementIndicesImpl(
-        isolate, object, backing_store, convert, filter, combined_keys,
-        &nof_indices);
+        isolate, object, backing_store,
+        needs_sorting ? GetKeysConversion::kKeepNumbers : convert, filter,
+        combined_keys, &nof_indices);
 
-    // Sort the indices list if necessary.
-    if (IsDictionaryElementsKind(kind()) || IsSloppyArgumentsElements(kind())) {
+    if (needs_sorting) {
       SortIndices(combined_keys, nof_indices, SKIP_WRITE_BARRIER);
       uint32_t array_length = 0;
       // Indices from dictionary elements should only be converted after
@@ -1021,7 +1024,9 @@ class ElementsAccessorBase : public ElementsAccessor {
     CopyObjectToObjectElements(*keys, FAST_ELEMENTS, 0, *combined_keys,
                                FAST_ELEMENTS, nof_indices, nof_property_keys);
 
-    if (IsHoleyElementsKind(kind())) {
+    // For holey elements and arguments we might have to shrink the collected
+    // keys since the estimates might be off.
+    if (IsHoleyElementsKind(kind()) || IsSloppyArgumentsElements(kind())) {
       // Shrink combined_keys to the final size.
       int final_size = nof_indices + nof_property_keys;
       DCHECK_LE(final_size, combined_keys->length());
@@ -2305,6 +2310,14 @@ class SloppyArgumentsElementsAccessor
            ArgumentsAccessor::GetCapacityImpl(holder, arguments);
   }
 
+  static uint32_t GetMaxNumberOfEntries(JSObject* holder,
+                                        FixedArrayBase* backing_store) {
+    FixedArray* parameter_map = FixedArray::cast(backing_store);
+    FixedArrayBase* arguments = FixedArrayBase::cast(parameter_map->get(1));
+    return parameter_map->length() - 2 +
+           ArgumentsAccessor::GetMaxNumberOfEntries(holder, arguments);
+  }
+
   static void AddElementsToKeyAccumulatorImpl(Handle<JSObject> receiver,
                                               KeyAccumulator* accumulator,
                                               AddKeyConversion convert) {