Update gc branch to bleeding_edge revision 8862.

src/elements.cc

+// Copyright 2011 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
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#include "v8.h"
+
+#include "objects.h"
+#include "elements.h"
+
+namespace v8 {
+namespace internal {
+
+
+ElementsAccessor** ElementsAccessor::elements_accessors_;
+
+
+// Base class for element handler implementations. Contains the
+// the common logic for objects with different ElementsKinds.
+// Subclasses must specialize method for which the element
+// implementation differs from the base class implementation.
+//
+// This class is intended to be used in the following way:
+//
+//   class SomeElementsAccessor :
+//       public ElementsAccessorBase<SomeElementsAccessor,
+//                                   BackingStoreClass> {
+//     ...
+//   }
+//
+// This is an example of the Curiously Recurring Template Pattern (see
+// http://en.wikipedia.org/wiki/Curiously_recurring_template_pattern).  We use
+// CRTP to guarantee aggressive compile time optimizations (i.e.  inlining and
+// specialization of SomeElementsAccessor methods).
+template <typename ElementsAccessorSubclass, typename BackingStoreClass>
+class ElementsAccessorBase : public ElementsAccessor {
+ public:
+  ElementsAccessorBase() { }
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    if (index < ElementsAccessorSubclass::GetLength(obj)) {
+      BackingStoreClass* backing_store =
+          ElementsAccessorSubclass::GetBackingStore(obj);
+      return backing_store->get(index);
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) = 0;
+
+ protected:
+  static BackingStoreClass* GetBackingStore(JSObject* obj) {
+    return BackingStoreClass::cast(obj->elements());
+  }
+
+  static uint32_t GetLength(JSObject* obj) {
+    return ElementsAccessorSubclass::GetBackingStore(obj)->length();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ElementsAccessorBase);
+};
+
+
+class FastElementsAccessor
+    : public ElementsAccessorBase<FastElementsAccessor, FixedArray> {
+ public:
+  static MaybeObject* DeleteCommon(JSObject* obj,
+                                   uint32_t index) {
+    ASSERT(obj->HasFastElements() || obj->HasFastArgumentsElements());
+    Heap* heap = obj->GetHeap();
+    FixedArray* backing_store = FixedArray::cast(obj->elements());
+    if (backing_store->map() == heap->non_strict_arguments_elements_map()) {
+      backing_store = FixedArray::cast(backing_store->get(1));
+    } else {
+      Object* writable;
+      MaybeObject* maybe = obj->EnsureWritableFastElements();
+      if (!maybe->ToObject(&writable)) return maybe;
+      backing_store = FixedArray::cast(writable);
+    }
+    uint32_t length = static_cast<uint32_t>(
+        obj->IsJSArray()
+        ? Smi::cast(JSArray::cast(obj)->length())->value()
+        : backing_store->length());
+    if (index < length) {
+      backing_store->set_the_hole(index);
+      // If an old space backing store is larger than a certain size and
+      // has too few used values, normalize it.
+      // To avoid doing the check on every delete we require at least
+      // one adjacent hole to the value being deleted.
+      Object* hole = heap->the_hole_value();
+      const int kMinLengthForSparsenessCheck = 64;
+      if (backing_store->length() >= kMinLengthForSparsenessCheck &&
+          !heap->InNewSpace(backing_store) &&
+          ((index > 0 && backing_store->get(index - 1) == hole) ||
+           (index + 1 < length && backing_store->get(index + 1) == hole))) {
+        int num_used = 0;
+        for (int i = 0; i < backing_store->length(); ++i) {
+          if (backing_store->get(i) != hole) ++num_used;
+          // Bail out early if more than 1/4 is used.
+          if (4 * num_used > backing_store->length()) break;
+        }
+        if (4 * num_used <= backing_store->length()) {
+          MaybeObject* result = obj->NormalizeElements();
+          if (result->IsFailure()) return result;
+        }
+      }
+    }
+    return heap->true_value();
+  }
+
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) {
+    return DeleteCommon(obj, index);
+  }
+};
+
+
+class FastDoubleElementsAccessor
+    : public ElementsAccessorBase<FastDoubleElementsAccessor,
+                                  FixedDoubleArray> {
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) {
+    int length = obj->IsJSArray()
+        ? Smi::cast(JSArray::cast(obj)->length())->value()
+        : FixedDoubleArray::cast(obj->elements())->length();
+    if (index < static_cast<uint32_t>(length)) {
+      FixedDoubleArray::cast(obj->elements())->set_the_hole(index);
+    }
+    return obj->GetHeap()->true_value();
+  }
+};
+
+
+// Super class for all external element arrays.
+template<typename ExternalElementsAccessorSubclass,
+         typename ExternalArray>
+class ExternalElementsAccessor
+    : public ElementsAccessorBase<ExternalElementsAccessorSubclass,
+                                  ExternalArray> {
+ public:
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    if (index < ExternalElementsAccessorSubclass::GetLength(obj)) {
+      ExternalArray* backing_store =
+          ExternalElementsAccessorSubclass::GetBackingStore(obj);
+      return backing_store->get(index);
+    } else {
+      return obj->GetHeap()->undefined_value();
+    }
+  }
+
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) {
+    // External arrays always ignore deletes.
+    return obj->GetHeap()->true_value();
+  }
+};
+
+
+class ExternalByteElementsAccessor
+    : public ExternalElementsAccessor<ExternalByteElementsAccessor,
+                                      ExternalByteArray> {
+};
+
+
+class ExternalUnsignedByteElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedByteElementsAccessor,
+                                      ExternalUnsignedByteArray> {
+};
+
+
+class ExternalShortElementsAccessor
+    : public ExternalElementsAccessor<ExternalShortElementsAccessor,
+                                      ExternalShortArray> {
+};
+
+
+class ExternalUnsignedShortElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedShortElementsAccessor,
+                                      ExternalUnsignedShortArray> {
+};
+
+
+class ExternalIntElementsAccessor
+    : public ExternalElementsAccessor<ExternalIntElementsAccessor,
+                                      ExternalIntArray> {
+};
+
+
+class ExternalUnsignedIntElementsAccessor
+    : public ExternalElementsAccessor<ExternalUnsignedIntElementsAccessor,
+                                      ExternalUnsignedIntArray> {
+};
+
+
+class ExternalFloatElementsAccessor
+    : public ExternalElementsAccessor<ExternalFloatElementsAccessor,
+                                      ExternalFloatArray> {
+};
+
+
+class ExternalDoubleElementsAccessor
+    : public ExternalElementsAccessor<ExternalDoubleElementsAccessor,
+                                      ExternalDoubleArray> {
+};
+
+
+class PixelElementsAccessor
+    : public ExternalElementsAccessor<PixelElementsAccessor,
+                                      ExternalPixelArray> {
+};
+
+
+class DictionaryElementsAccessor
+    : public ElementsAccessorBase<DictionaryElementsAccessor,
+                                  NumberDictionary> {
+ public:
+  static MaybeObject* GetNumberDictionaryElement(
+      JSObject* obj,
+      Object* receiver,
+      NumberDictionary* backing_store,
+      uint32_t index) {
+    int entry = backing_store->FindEntry(index);
+    if (entry != NumberDictionary::kNotFound) {
+      Object* element = backing_store->ValueAt(entry);
+      PropertyDetails details = backing_store->DetailsAt(entry);
+      if (details.type() == CALLBACKS) {
+        return obj->GetElementWithCallback(receiver,
+                                           element,
+                                           index,
+                                           obj);
+      } else {
+        return element;
+      }
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+
+  static MaybeObject* DeleteCommon(JSObject* obj,
+                                   uint32_t index,
+                                   JSReceiver::DeleteMode mode) {
+    Isolate* isolate = obj->GetIsolate();
+    Heap* heap = isolate->heap();
+    FixedArray* backing_store = FixedArray::cast(obj->elements());
+    bool is_arguments =
+        (obj->GetElementsKind() == JSObject::NON_STRICT_ARGUMENTS_ELEMENTS);
+    if (is_arguments) {
+      backing_store = FixedArray::cast(backing_store->get(1));
+    }
+    NumberDictionary* dictionary = NumberDictionary::cast(backing_store);
+    int entry = dictionary->FindEntry(index);
+    if (entry != NumberDictionary::kNotFound) {
+      Object* result = dictionary->DeleteProperty(entry, mode);
+      if (result == heap->true_value()) {
+        MaybeObject* maybe_elements = dictionary->Shrink(index);
+        FixedArray* new_elements = NULL;
+        if (!maybe_elements->To(&new_elements)) {
+          return maybe_elements;
+        }
+        if (is_arguments) {
+          FixedArray::cast(obj->elements())->set(1, new_elements);
+        } else {
+          obj->set_elements(new_elements);
+        }
+      }
+      if (mode == JSObject::STRICT_DELETION &&
+          result == heap->false_value()) {
+        // In strict mode, attempting to delete a non-configurable property
+        // throws an exception.
+        HandleScope scope(isolate);
+        Handle<Object> holder(obj);
+        Handle<Object> name = isolate->factory()->NewNumberFromUint(index);
+        Handle<Object> args[2] = { name, holder };
+        Handle<Object> error =
+            isolate->factory()->NewTypeError("strict_delete_property",
+                                             HandleVector(args, 2));
+        return isolate->Throw(*error);
+      }
+    }
+    return heap->true_value();
+  }
+
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) {
+    return DeleteCommon(obj, index, mode);
+  }
+
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    return GetNumberDictionaryElement(obj,
+                                      receiver,
+                                      obj->element_dictionary(),
+                                      index);
+  }
+};
+
+
+class NonStrictArgumentsElementsAccessor
+    : public ElementsAccessorBase<NonStrictArgumentsElementsAccessor,
+                                  FixedArray> {
+ public:
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    FixedArray* parameter_map = GetBackingStore(obj);
+    uint32_t length = parameter_map->length();
+    Object* probe =
+        (index < length - 2) ? parameter_map->get(index + 2) : NULL;
+    if (probe != NULL && !probe->IsTheHole()) {
+      Context* context = Context::cast(parameter_map->get(0));
+      int context_index = Smi::cast(probe)->value();
+      ASSERT(!context->get(context_index)->IsTheHole());
+      return context->get(context_index);
+    } else {
+      // Object is not mapped, defer to the arguments.
+      FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
+      if (arguments->IsDictionary()) {
+        return DictionaryElementsAccessor::GetNumberDictionaryElement(
+            obj,
+            receiver,
+            NumberDictionary::cast(arguments),
+            index);
+      } else if (index < static_cast<uint32_t>(arguments->length())) {
+        return arguments->get(index);
+      }
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+  virtual MaybeObject* Delete(JSObject* obj,
+                              uint32_t index,
+                              JSReceiver::DeleteMode mode) {
+    FixedArray* parameter_map = FixedArray::cast(obj->elements());
+    uint32_t length = parameter_map->length();
+    Object* probe =
+        index < (length - 2) ? parameter_map->get(index + 2) : NULL;
+    if (probe != NULL && !probe->IsTheHole()) {
+      // TODO(kmillikin): We could check if this was the last aliased
+      // parameter, and revert to normal elements in that case.  That
+      // would enable GC of the context.
+      parameter_map->set_the_hole(index + 2);
+    } else {
+      FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
+      if (arguments->IsDictionary()) {
+        return DictionaryElementsAccessor::DeleteCommon(obj, index, mode);
+      } else {
+        return FastElementsAccessor::DeleteCommon(obj, index);
+      }
+    }
+    return obj->GetHeap()->true_value();
+  }
+};
+
+
+void ElementsAccessor::InitializeOncePerProcess() {
+  static struct ConcreteElementsAccessors {
+    FastElementsAccessor fast_elements_handler;
+    FastDoubleElementsAccessor fast_double_elements_handler;
+    DictionaryElementsAccessor dictionary_elements_handler;
+    NonStrictArgumentsElementsAccessor non_strict_arguments_elements_handler;
+    ExternalByteElementsAccessor byte_elements_handler;
+    ExternalUnsignedByteElementsAccessor unsigned_byte_elements_handler;
+    ExternalShortElementsAccessor short_elements_handler;
+    ExternalUnsignedShortElementsAccessor unsigned_short_elements_handler;
+    ExternalIntElementsAccessor int_elements_handler;
+    ExternalUnsignedIntElementsAccessor unsigned_int_elements_handler;
+    ExternalFloatElementsAccessor float_elements_handler;
+    ExternalDoubleElementsAccessor double_elements_handler;
+    PixelElementsAccessor pixel_elements_handler;
+  } element_accessors;
+
+  static ElementsAccessor* accessor_array[] = {
+    &element_accessors.fast_elements_handler,
+    &element_accessors.fast_double_elements_handler,
+    &element_accessors.dictionary_elements_handler,
+    &element_accessors.non_strict_arguments_elements_handler,
+    &element_accessors.byte_elements_handler,
+    &element_accessors.unsigned_byte_elements_handler,
+    &element_accessors.short_elements_handler,
+    &element_accessors.unsigned_short_elements_handler,
+    &element_accessors.int_elements_handler,
+    &element_accessors.unsigned_int_elements_handler,
+    &element_accessors.float_elements_handler,
+    &element_accessors.double_elements_handler,
+    &element_accessors.pixel_elements_handler
+  };
+
+  elements_accessors_ = accessor_array;
+}
+
+
+} }  // namespace v8::internal