Revert of Array.prototype.unshift builtin improvements

src/elements.cc

Index: src/elements.cc
diff --git a/src/elements.cc b/src/elements.cc
index d36f7a4e4961798dc309a858a2f650f2cdfcded7..e133f8f738eb0bcf0b90c822e13c3a80d45e0b79 100644
--- a/src/elements.cc
+++ b/src/elements.cc
@@ -585,20 +585,6 @@
     return 0;
   }
 
-  virtual uint32_t Unshift(Handle<JSArray> receiver,
-                           Handle<FixedArrayBase> backing_store, Arguments args,
-                           uint32_t add_count) {
-    return ElementsAccessorSubclass::UnshiftImpl(receiver, backing_store, args,
-                                                 add_count);
-  }
-
-  static uint32_t UnshiftImpl(Handle<JSArray> receiver,
-                              Handle<FixedArrayBase> backing_store,
-                              Arguments args, uint32_t add_count) {
-    UNREACHABLE();
-    return 0;
-  }
-
   virtual Handle<JSArray> Splice(Handle<JSArray> receiver,
                                  Handle<FixedArrayBase> backing_store,
                                  uint32_t start, uint32_t delete_count,
@@ -1195,50 +1181,6 @@
 #endif
   }
 
-
-  static uint32_t UnshiftImpl(Handle<JSArray> receiver,
-                              Handle<FixedArrayBase> backing_store,
-                              Arguments args, uint32_t add_count) {
-    int len = Smi::cast(receiver->length())->value();
-    if (add_count == 0) {
-      return len;
-    }
-    // Currently fixed arrays cannot grow too big, so
-    // we should never hit this case.
-    DCHECK(add_count <= static_cast<uint32_t>(Smi::kMaxValue - len));
-    int new_length = len + add_count;
-    Handle<FixedArrayBase> new_elements;
-
-    if (new_length > backing_store->length()) {
-      // New backing storage is needed.
-      int capacity = new_length + (new_length >> 1) + 16;
-      new_elements = FastElementsAccessorSubclass::ConvertElementsWithCapacity(
-          receiver, backing_store, KindTraits::Kind, capacity, 0);
-      FastElementsAccessorSubclass::CopyElementsImpl(
-          *backing_store, 0, *new_elements, KindTraits::Kind, add_count,
-          kPackedSizeNotKnown, ElementsAccessor::kCopyToEndAndInitializeToHole);
-    } else {
-      DisallowHeapAllocation no_gc;
-      Heap* heap = receiver->GetIsolate()->heap();
-      FastElementsAccessorSubclass::MoveElements(heap, backing_store, add_count,
-                                                 0, len, 0, 0);
-      new_elements = backing_store;
-    }
-
-    // Add the provided values.
-    DisallowHeapAllocation no_gc;
-    for (uint32_t i = 0; i < add_count; i++) {
-      FastElementsAccessorSubclass::SetImpl(*new_elements, i, args[i + 1]);
-    }
-    if (!new_elements.is_identical_to(backing_store)) {
-      receiver->set_elements(*new_elements);
-    }
-    // Set the length.
-    receiver->set_length(Smi::FromInt(new_length));
-    return new_length;
-  }
-
-
   static uint32_t PushImpl(Handle<JSArray> receiver,
                            Handle<FixedArrayBase> backing_store,
                            Object** objects, uint32_t push_size,
@@ -1247,13 +1189,14 @@
     if (push_size == 0) {
       return len;
     }
+    uint32_t elms_len = backing_store->length();
     // Currently fixed arrays cannot grow too big, so
     // we should never hit this case.
     DCHECK(push_size <= static_cast<uint32_t>(Smi::kMaxValue - len));
     uint32_t new_length = len + push_size;
     Handle<FixedArrayBase> new_elms;
 
-    if (new_length > static_cast<uint32_t>(backing_store->length())) {
+    if (new_length > elms_len) {
       // New backing storage is needed.
       uint32_t capacity = new_length + (new_length >> 1) + 16;
       new_elms = FastElementsAccessorSubclass::ConvertElementsWithCapacity(
@@ -1328,10 +1271,19 @@
     }
 
     // Copy new Elements from args
-    DisallowHeapAllocation no_gc;
-    for (uint32_t index = start; index < start + add_count; index++) {
-      Object* object = args[3 + index - start];
-      FastElementsAccessorSubclass::SetImpl(*backing_store, index, object);
+    if (IsFastDoubleElementsKind(KindTraits::Kind)) {
+      for (uint32_t index = start; index < start + add_count; index++) {
+        Object* arg = args[3 + index - start];
+        FastElementsAccessorSubclass::SetImpl(*backing_store, index, arg);
+      }
+    } else {
+      // FastSmiOrObjectElementsKind
+      Handle<FixedArray> elms = Handle<FixedArray>::cast(backing_store);
+      DisallowHeapAllocation no_gc;
+      WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
+      for (uint32_t index = start; index < start + add_count; index++) {
+        elms->set(index, args[3 + index - start], mode);
+      }
     }
 
     if (elms_changed) {