Encapsulate element handling into a class keyed on ElementsKind

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 {
+
+
+// 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 SomeElementsHandlerImpl :
+//       public ElementsHandlerImpl<SomeElementsHandlerImpl> {

[Jakob Kummerow, 2011/07/30 10:29:21]

nit: second template argument (BackingStoreClass) is missing in this example.

[danno, 2011/07/30 13:10:10]

Done.

+//     ...
+//   }
+//
+// This is an example of 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 SomeElementsHandlerImpl methods).
+template <typename ConcreteHandlerImpl, typename BackingStoreClass>
+class ElementsHandlerImpl {
+ public:
+  static MaybeObject* GetWithReceiver(JSObject* obj,
+                                      Object* receiver,
+                                      uint32_t index) {
+    if (index < ConcreteHandlerImpl::GetLength(obj)) {
+      BackingStoreClass* backing_store =
+          ElementsHandlerImpl::GetBackingStore(obj);
+      MaybeObject* result = backing_store->get(index);
+      if (!result->IsTheHole()) return result;
+    }
+
+    Object* pt = obj->GetPrototype();
+    Heap* heap = obj->GetHeap();
+    if (pt == heap->null_value()) return heap->undefined_value();
+    return pt->GetElementWithReceiver(receiver, index);
+  }
+
+ protected:
+  static BackingStoreClass* GetBackingStore(JSObject* obj) {
+    return BackingStoreClass::cast(obj->elements());
+  }
+
+  static uint32_t GetLength(JSObject* obj) {
+    return ConcreteHandlerImpl::GetBackingStore(obj)->length();
+  }
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(ElementsHandlerImpl);
+};
+
+
+class FastElementsHandlerImpl
+    : public ElementsHandlerImpl< FastElementsHandlerImpl, FixedArray> {

[Jakob Kummerow, 2011/07/30 10:29:21]

nit: extra space

[danno, 2011/07/30 13:10:10]

Done.

+};
+
+
+class FastDoubleElementsHandlerImpl
+    : public ElementsHandlerImpl<FastDoubleElementsHandlerImpl,
+                                 FixedDoubleArray> {
+};
+
+
+// Super class for all external element arrays, whose handler implementation is
+// identical except for specialization.
+template<typename ConcreteExternalElementHandlerImpl,
+         typename ExternalArray>
+class ExternalElementsHandlerImpl
+    : public ElementsHandlerImpl<ConcreteExternalElementHandlerImpl,
+                                 ExternalArray> {
+};
+
+
+class ExternalByteElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalByteElementsHandlerImpl,
+                                         ExternalByteArray> {
+};
+
+
+class ExternalUnsignedByteElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<
+  ExternalUnsignedByteElementsHandlerImpl, ExternalUnsignedByteArray> {
+};
+
+
+class ExternalShortElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalShortElementsHandlerImpl,
+                                         ExternalShortArray> {
+};
+
+
+class ExternalUnsignedShortElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<
+  ExternalUnsignedShortElementsHandlerImpl, ExternalUnsignedShortArray> {
+};
+
+
+class ExternalIntElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalIntElementsHandlerImpl,
+                                         ExternalIntArray> {
+};
+
+
+class ExternalUnsignedIntElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalUnsignedIntElementsHandlerImpl,
+                                         ExternalUnsignedIntArray> {
+};
+
+
+class ExternalFloatElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalFloatElementsHandlerImpl,
+                                         ExternalFloatArray> {
+};
+
+
+class ExternalDoubleElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<ExternalDoubleElementsHandlerImpl,
+                                         ExternalDoubleArray> {
+};
+
+
+class PixelElementsHandlerImpl
+    : public ExternalElementsHandlerImpl<PixelElementsHandlerImpl,
+                                         ExternalPixelArray> {
+};
+
+
+class DictionaryElementsHandlerImpl
+    : public ElementsHandlerImpl<DictionaryElementsHandlerImpl,
+                                 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);
+      }
+      return element;
+    }
+    return obj->GetHeap()->the_hole_value();
+  }
+
+  static MaybeObject* GetWithReceiver(JSObject* obj,
+                                      Object* receiver,
+                                      uint32_t index) {
+    NumberDictionary* backing_store = GetBackingStore(obj);
+    return GetNumberDictionaryElement(obj, receiver, backing_store, index);
+  }
+
+ protected:
+  static NumberDictionary* GetBackingStore(JSObject* obj) {
+    return NumberDictionary::cast(obj->element_dictionary());
+  }
+};
+
+
+class NonStrictArgumentsElementsHandlerImpl
+    : public ElementsHandlerImpl<NonStrictArgumentsElementsHandlerImpl,
+                                 FixedArray> {
+ public:
+  static 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 DictionaryElementsHandlerImpl::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();
+  }
+};
+
+
+template<typename Impl>
+class ConcreteElementsHandler : public ElementsHandler {
+ public:
+  ConcreteElementsHandler() {}
+
+  virtual MaybeObject* GetWithReceiver(JSObject* obj,
+                                       Object* receiver,
+                                       uint32_t index) {
+    return Impl::GetWithReceiver(obj,
+                                 receiver,
+                                 index);
+  }
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ConcreteElementsHandler);
+};
+
+
+struct ConcreteElementHandlers {

[Jakob Kummerow, 2011/07/30 10:29:21]

nit: for consistency, change order to match elements_handler_table_? (I.e. move
up "dictionary" and "non_strict_arguments".)

[danno, 2011/07/30 13:10:10]

Done.

+  ConcreteElementsHandler<FastElementsHandlerImpl>
+      fast_elements_handler;
+  ConcreteElementsHandler<FastDoubleElementsHandlerImpl>
+      fast_double_elements_handler;
+  ConcreteElementsHandler<ExternalByteElementsHandlerImpl>
+      byte_elements_handler;
+  ConcreteElementsHandler<ExternalUnsignedByteElementsHandlerImpl>
+      unsigned_byte_elements_handler;
+  ConcreteElementsHandler<ExternalShortElementsHandlerImpl>
+      short_elements_handler;
+  ConcreteElementsHandler<ExternalUnsignedShortElementsHandlerImpl>
+      unsigned_short_elements_handler;
+  ConcreteElementsHandler<ExternalIntElementsHandlerImpl>
+      int_elements_handler;
+  ConcreteElementsHandler<ExternalUnsignedIntElementsHandlerImpl>
+      unsigned_int_elements_handler;
+  ConcreteElementsHandler<ExternalFloatElementsHandlerImpl>
+      float_elements_handler;
+  ConcreteElementsHandler<ExternalDoubleElementsHandlerImpl>
+      double_elements_handler;
+  ConcreteElementsHandler<PixelElementsHandlerImpl>
+      pixel_elements_handler;
+  ConcreteElementsHandler<DictionaryElementsHandlerImpl>
+      dictionary_elements_handler;
+  ConcreteElementsHandler<NonStrictArgumentsElementsHandlerImpl>
+      non_strict_arguments_elements_handler;
+} element_handlers;
+
+
+ElementsHandler* ElementsHandler::elements_handler_table_[] = {
+  &element_handlers.fast_elements_handler,
+  &element_handlers.fast_double_elements_handler,
+  &element_handlers.dictionary_elements_handler,
+  &element_handlers.non_strict_arguments_elements_handler,
+  &element_handlers.byte_elements_handler,
+  &element_handlers.unsigned_byte_elements_handler,
+  &element_handlers.short_elements_handler,
+  &element_handlers.unsigned_short_elements_handler,
+  &element_handlers.int_elements_handler,
+  &element_handlers.unsigned_int_elements_handler,
+  &element_handlers.float_elements_handler,
+  &element_handlers.double_elements_handler,
+  &element_handlers.pixel_elements_handler
+};
+
+
+} }  // namespace v8::internal