Adding ElementsAccessor::Splice

src/builtins.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/v8.h"
 
 #include "src/api.h"
 #include "src/api-natives.h"
 #include "src/arguments.h"
 #include "src/base/once.h"
@@ skipping 158 matching lines @@
   UNREACHABLE();
   return isolate->heap()->undefined_value();  // Make compiler happy.
 }
 
 
 BUILTIN(EmptyFunction) {
   return isolate->heap()->undefined_value();
 }
 
 
+// TODO(cbruni): check if this is a suitable method on Object
+bool ClampedToInteger(Object* object, int* out) {

[mvstanton, 2015/08/20 10:45:33]

I like this method much better, thanks for addressing!

+  // This is an extended version of ECMA-262 9.4, but additionally
+  // clamps values to [kMinInt, kMaxInt]
+  if (object->IsSmi()) {
+    *out = Smi::cast(object)->value();
+    return true;
+  } else if (object->IsHeapNumber()) {
+    *out = FastD2IChecked(HeapNumber::cast(object)->value());
+    return true;
+  } else if (object->IsUndefined()) {
+    *out = 0;
+    return true;
+  } else if (object->IsBoolean()) {
+    *out = (Oddball::cast(object)->kind() == Oddball::kTrue) ? 1 : 0;
+    return true;
+  }
+  return false;
+}
+
+
 static void MoveDoubleElements(FixedDoubleArray* dst, int dst_index,
                                FixedDoubleArray* src, int src_index, int len) {
   if (len == 0) return;
   MemMove(dst->data_start() + dst_index, src->data_start() + src_index,
           len * kDoubleSize);
 }
 
 
 static bool ArrayPrototypeHasNoElements(PrototypeIterator* iter) {
   DisallowHeapAllocation no_gc;
@@ skipping 425 matching lines @@
 
   ElementsAccessor* accessor = object->GetElementsAccessor();
   accessor->CopyElements(
       elms, k, kind, handle(result_array->elements(), isolate), 0, result_len);
   return *result_array;
 }
 
 
 BUILTIN(ArraySplice) {
   HandleScope scope(isolate);
-  Heap* heap = isolate->heap();
   Handle<Object> receiver = args.receiver();
   MaybeHandle<FixedArrayBase> maybe_elms_obj =
       EnsureJSArrayWithWritableFastElements(isolate, receiver, &args, 3);
   Handle<FixedArrayBase> elms_obj;
   if (!maybe_elms_obj.ToHandle(&elms_obj)) {
     return CallJsBuiltin(isolate, "$arraySplice", args);
   }
   Handle<JSArray> array = Handle<JSArray>::cast(receiver);
   DCHECK(!array->map()->is_observed());
 
-  int len = Smi::cast(array->length())->value();
-
-  int n_arguments = args.length() - 1;
-
+  int argument_count = args.length() - 1;
   int relative_start = 0;
-  if (n_arguments > 0) {
+  if (argument_count > 0) {
     DisallowHeapAllocation no_gc;
-    Object* arg1 = args[1];
-    if (arg1->IsSmi()) {
-      relative_start = Smi::cast(arg1)->value();
-    } else if (arg1->IsHeapNumber()) {
-      double start = HeapNumber::cast(arg1)->value();
-      if (start < kMinInt || start > kMaxInt) {
-        AllowHeapAllocation allow_allocation;
-        return CallJsBuiltin(isolate, "$arraySplice", args);
-      }
-      relative_start = std::isnan(start) ? 0 : static_cast<int>(start);
-    } else if (!arg1->IsUndefined()) {
+    if (!ClampedToInteger(args[1], &relative_start)) {
       AllowHeapAllocation allow_allocation;
       return CallJsBuiltin(isolate, "$arraySplice", args);
     }
   }
+  int len = Smi::cast(array->length())->value();
+  // clip relative start to [0, len]
   int actual_start = (relative_start < 0) ? Max(len + relative_start, 0)
                                           : Min(relative_start, len);
 
-  // SpiderMonkey, TraceMonkey and JSC treat the case where no delete count is
-  // given as a request to delete all the elements from the start.
-  // And it differs from the case of undefined delete count.
-  // This does not follow ECMA-262, but we do the same for
-  // compatibility.
   int actual_delete_count;
-  if (n_arguments == 1) {
+  if (argument_count == 1) {
+    // SpiderMonkey, TraceMonkey and JSC treat the case where no delete count is
+    // given as a request to delete all the elements from the start.
+    // And it differs from the case of undefined delete count.
+    // This does not follow ECMA-262, but we do the same for compatibility.
     DCHECK(len - actual_start >= 0);
     actual_delete_count = len - actual_start;
   } else {
-    int value = 0;  // ToInteger(undefined) == 0
-    if (n_arguments > 1) {
-      DisallowHeapAllocation no_gc;
-      Object* arg2 = args[2];
-      if (arg2->IsSmi()) {
-        value = Smi::cast(arg2)->value();
-      } else {
+    int delete_count = 0;
+    DisallowHeapAllocation no_gc;
+    if (argument_count > 1) {
+      if (!ClampedToInteger(args[2], &delete_count)) {
         AllowHeapAllocation allow_allocation;
         return CallJsBuiltin(isolate, "$arraySplice", args);
       }
     }
-    actual_delete_count = Min(Max(value, 0), len - actual_start);
+    actual_delete_count = Min(Max(delete_count, 0), len - actual_start);
   }
 
-  ElementsKind elements_kind = array->GetElementsKind();
-
-  int item_count = (n_arguments > 1) ? (n_arguments - 2) : 0;
-  int new_length = len - actual_delete_count + item_count;
-
-  // For double mode we do not support changing the length.
-  if (new_length > len && IsFastDoubleElementsKind(elements_kind)) {
-    return CallJsBuiltin(isolate, "$arraySplice", args);
-  }
+  int add_count = (argument_count > 1) ? (argument_count - 2) : 0;
+  int new_length = len - actual_delete_count + add_count;
 
   if (new_length != len && JSArray::HasReadOnlyLength(array)) {
     AllowHeapAllocation allow_allocation;
     return CallJsBuiltin(isolate, "$arraySplice", args);
   }
-
-  if (new_length == 0) {
-    Handle<JSArray> result = isolate->factory()->NewJSArrayWithElements(
-        elms_obj, elements_kind, actual_delete_count);
-    array->set_elements(heap->empty_fixed_array());
-    array->set_length(Smi::FromInt(0));
-    return *result;
-  }
-
-  Handle<JSArray> result_array =
-      isolate->factory()->NewJSArray(elements_kind,
-                                     actual_delete_count,
-                                     actual_delete_count);
-
-  if (actual_delete_count > 0) {
-    DisallowHeapAllocation no_gc;
-    ElementsAccessor* accessor = array->GetElementsAccessor();
-    accessor->CopyElements(
-        elms_obj, actual_start, elements_kind,
-        handle(result_array->elements(), isolate), 0, actual_delete_count);
-  }
-
-  bool elms_changed = false;
-  if (item_count < actual_delete_count) {
-    // Shrink the array.
-    const bool trim_array = !heap->lo_space()->Contains(*elms_obj) &&
-      ((actual_start + item_count) <
-          (len - actual_delete_count - actual_start));
-    if (trim_array) {
-      const int delta = actual_delete_count - item_count;
-
-      if (elms_obj->IsFixedDoubleArray()) {
-        Handle<FixedDoubleArray> elms =
-            Handle<FixedDoubleArray>::cast(elms_obj);
-        MoveDoubleElements(*elms, delta, *elms, 0, actual_start);
-      } else {
-        Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
-        DisallowHeapAllocation no_gc;
-        heap->MoveElements(*elms, delta, 0, actual_start);
-      }
-
-      if (heap->CanMoveObjectStart(*elms_obj)) {
-        // On the fast path we move the start of the object in memory.
-        elms_obj = handle(heap->LeftTrimFixedArray(*elms_obj, delta));
-      } else {
-        // This is the slow path. We are going to move the elements to the left
-        // by copying them. For trimmed values we store the hole.
-        if (elms_obj->IsFixedDoubleArray()) {
-          Handle<FixedDoubleArray> elms =
-              Handle<FixedDoubleArray>::cast(elms_obj);
-          MoveDoubleElements(*elms, 0, *elms, delta, len - delta);
-          elms->FillWithHoles(len - delta, len);
-        } else {
-          Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
-          DisallowHeapAllocation no_gc;
-          heap->MoveElements(*elms, 0, delta, len - delta);
-          elms->FillWithHoles(len - delta, len);
-        }
-      }
-      elms_changed = true;
-    } else {
-      if (elms_obj->IsFixedDoubleArray()) {
-        Handle<FixedDoubleArray> elms =
-            Handle<FixedDoubleArray>::cast(elms_obj);
-        MoveDoubleElements(*elms, actual_start + item_count,
-                           *elms, actual_start + actual_delete_count,
-                           (len - actual_delete_count - actual_start));
-        elms->FillWithHoles(new_length, len);
-      } else {
-        Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
-        DisallowHeapAllocation no_gc;
-        heap->MoveElements(*elms, actual_start + item_count,
-                           actual_start + actual_delete_count,
-                           (len - actual_delete_count - actual_start));
-        elms->FillWithHoles(new_length, len);
-      }
-    }
-  } else if (item_count > actual_delete_count) {
-    Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
-    // Currently fixed arrays cannot grow too big, so
-    // we should never hit this case.
-    DCHECK((item_count - actual_delete_count) <= (Smi::kMaxValue - len));
-
-    // Check if array need to grow.
-    if (new_length > elms->length()) {
-      // New backing storage is needed.
-      int capacity = new_length + (new_length >> 1) + 16;
-      Handle<FixedArray> new_elms =
-          isolate->factory()->NewUninitializedFixedArray(capacity);
-
-      DisallowHeapAllocation no_gc;
-
-      ElementsKind kind = array->GetElementsKind();
-      ElementsAccessor* accessor = array->GetElementsAccessor();
-      if (actual_start > 0) {
-        // Copy the part before actual_start as is.
-        accessor->CopyElements(
-            elms, 0, kind, new_elms, 0, actual_start);
-      }
-      accessor->CopyElements(
-          elms, actual_start + actual_delete_count, kind,
-          new_elms, actual_start + item_count,
-          ElementsAccessor::kCopyToEndAndInitializeToHole);
-
-      elms_obj = new_elms;
-      elms_changed = true;
-    } else {
-      DisallowHeapAllocation no_gc;
-      heap->MoveElements(*elms, actual_start + item_count,
-                         actual_start + actual_delete_count,
-                         (len - actual_delete_count - actual_start));
-    }
-  }
-
-  if (IsFastDoubleElementsKind(elements_kind)) {
-    Handle<FixedDoubleArray> elms = Handle<FixedDoubleArray>::cast(elms_obj);
-    for (int k = actual_start; k < actual_start + item_count; k++) {
-      Object* arg = args[3 + k - actual_start];
-      if (arg->IsSmi()) {
-        elms->set(k, Smi::cast(arg)->value());
-      } else {
-        elms->set(k, HeapNumber::cast(arg)->value());
-      }
-    }
-  } else {
-    Handle<FixedArray> elms = Handle<FixedArray>::cast(elms_obj);
-    DisallowHeapAllocation no_gc;
-    WriteBarrierMode mode = elms->GetWriteBarrierMode(no_gc);
-    for (int k = actual_start; k < actual_start + item_count; k++) {
-      elms->set(k, args[3 + k - actual_start], mode);
-    }
-  }
-
-  if (elms_changed) {
-    array->set_elements(*elms_obj);
-  }
-  // Set the length.
-  array->set_length(Smi::FromInt(new_length));
-
-  return *result_array;
+  ElementsAccessor* accessor = array->GetElementsAccessor();
+  Handle<JSArray> result = accessor->Splice(
+      array, elms_obj, actual_start, actual_delete_count, args, add_count);
+  return *result;
 }
 
 
 BUILTIN(ArrayConcat) {
   HandleScope scope(isolate);
 
   int n_arguments = args.length();
   int result_len = 0;
   ElementsKind elements_kind = GetInitialFastElementsKind();
   bool has_double = false;
@@ skipping 686 matching lines @@
 BUILTIN_LIST_C(DEFINE_BUILTIN_ACCESSOR_C)
 BUILTIN_LIST_A(DEFINE_BUILTIN_ACCESSOR_A)
 BUILTIN_LIST_H(DEFINE_BUILTIN_ACCESSOR_H)
 BUILTIN_LIST_DEBUG_A(DEFINE_BUILTIN_ACCESSOR_A)
 #undef DEFINE_BUILTIN_ACCESSOR_C
 #undef DEFINE_BUILTIN_ACCESSOR_A
 
 
 }  // namespace internal
 }  // namespace v8