Implement efficient element copying in ElementsAccessors.

Review URL: https://chromiumcodereview.appspot.com/9638014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10989 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/builtins.cc

@@ -310,28 +310,6 @@ BUILTIN(ArrayCodeGeneric) {
 }
 
 
-static void CopyElements(Heap* heap,
-                         AssertNoAllocation* no_gc,
-                         FixedArray* dst,
-                         int dst_index,
-                         FixedArray* src,
-                         int src_index,
-                         int len) {
-  if (len == 0) return;
-  ASSERT(dst != src);  // Use MoveElements instead.
-  ASSERT(dst->map() != HEAP->fixed_cow_array_map());
-  ASSERT(len > 0);
-  CopyWords(dst->data_start() + dst_index,
-            src->data_start() + src_index,
-            len);
-  WriteBarrierMode mode = dst->GetWriteBarrierMode(*no_gc);
-  if (mode == UPDATE_WRITE_BARRIER) {
-    heap->RecordWrites(dst->address(), dst->OffsetOfElementAt(dst_index), len);
-  }
-  heap->incremental_marking()->RecordWrites(dst);
-}
-
-
 static void MoveElements(Heap* heap,
                          AssertNoAllocation* no_gc,
                          FixedArray* dst,
@@ -531,7 +509,8 @@ BUILTIN(ArrayPush) {
     FixedArray* new_elms = FixedArray::cast(obj);
 
     AssertNoAllocation no_gc;
-    CopyElements(heap, &no_gc, new_elms, 0, elms, 0, len);
+    CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, 0,
+                               new_elms, FAST_ELEMENTS, 0, len);
     FillWithHoles(heap, new_elms, new_length, capacity);
 
     elms = new_elms;
@@ -667,7 +646,8 @@ BUILTIN(ArrayUnshift) {
     }
     FixedArray* new_elms = FixedArray::cast(obj);
     AssertNoAllocation no_gc;
-    CopyElements(heap, &no_gc, new_elms, to_add, elms, 0, len);
+    CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, 0,
+                               new_elms, FAST_ELEMENTS, to_add, len);
     FillWithHoles(heap, new_elms, new_length, capacity);
     elms = new_elms;
     array->set_elements(elms);
@@ -778,8 +758,9 @@ BUILTIN(ArraySlice) {
   if (!maybe_array->To(&result_array)) return maybe_array;
 
   AssertNoAllocation no_gc;
-  CopyElements(heap, &no_gc, FixedArray::cast(result_array->elements()), 0,
-               elms, k, result_len);
+  CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, k,
+                             FixedArray::cast(result_array->elements()),
+                             FAST_ELEMENTS, 0, result_len);
 
   return result_array;
 }
@@ -852,11 +833,9 @@ BUILTIN(ArraySplice) {
   {
     AssertNoAllocation no_gc;
     // Fill newly created array.
-    CopyElements(heap,
-                 &no_gc,
-                 FixedArray::cast(result_array->elements()), 0,
-                 elms, actual_start,
-                 actual_delete_count);
+    CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, actual_start,
+                               FixedArray::cast(result_array->elements()),
+                               FAST_ELEMENTS, 0, actual_delete_count);
   }
 
   int item_count = (n_arguments > 1) ? (n_arguments - 2) : 0;
@@ -906,12 +885,13 @@ BUILTIN(ArraySplice) {
       {
         AssertNoAllocation no_gc;
         // Copy the part before actual_start as is.
-        CopyElements(heap, &no_gc, new_elms, 0, elms, 0, actual_start);
+        CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, 0,
+                                   new_elms, FAST_ELEMENTS, 0, actual_start);
         const int to_copy = len - actual_delete_count - actual_start;
-        CopyElements(heap, &no_gc,
-                     new_elms, actual_start + item_count,
-                     elms, actual_start + actual_delete_count,
-                     to_copy);
+        CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS,
+                                   actual_start + actual_delete_count,
+                                   new_elms, FAST_ELEMENTS,
+                                   actual_start + item_count, to_copy);
       }
 
       FillWithHoles(heap, new_elms, new_length, capacity);
@@ -1000,7 +980,9 @@ BUILTIN(ArrayConcat) {
     JSArray* array = JSArray::cast(args[i]);
     int len = Smi::cast(array->length())->value();
     FixedArray* elms = FixedArray::cast(array->elements());
-    CopyElements(heap, &no_gc, result_elms, start_pos, elms, 0, len);
+    CopyObjectToObjectElements(&no_gc, elms, FAST_ELEMENTS, 0,
+                               result_elms, FAST_ELEMENTS,
+                               start_pos, len);
     start_pos += len;
   }
   ASSERT(start_pos == result_len);

src/elements.h

@@ -29,6 +29,8 @@
 #define V8_ELEMENTS_H_
 
 #include "objects.h"
+#include "heap.h"
+#include "isolate.h"
 
 namespace v8 {
 namespace internal {
@@ -40,7 +42,8 @@ class ElementsAccessor {
   explicit ElementsAccessor(const char* name) : name_(name) { }
   virtual ~ElementsAccessor() { }
 
-  virtual const char* name() const { return name_; }
+  virtual ElementsKind kind() const = 0;
+  const char* name() const { return name_; }
 
   // Returns true if a holder contains an element with the specified key
   // without iterating up the prototype chain.  The caller can optionally pass
@@ -85,6 +88,25 @@ class ElementsAccessor {
                               uint32_t key,
                               JSReceiver::DeleteMode mode) = 0;
 
+  // Copy elements from one backing store to another. Typically, callers specify
+  // the source JSObject or JSArray in source_holder. If the holder's backing
+  // store is available, it can be passed in source and source_holder is
+  // ignored.
+  virtual MaybeObject* CopyElements(JSObject* source_holder,
+                                    uint32_t source_start,
+                                    FixedArrayBase* destination,
+                                    ElementsKind destination_kind,
+                                    uint32_t destination_start,
+                                    int copy_size,
+                                    FixedArrayBase* source = NULL) = 0;
+
+  MaybeObject* CopyElements(JSObject* from_holder,
+                            FixedArrayBase* to,
+                            ElementsKind to_kind,
+                            FixedArrayBase* from = NULL) {
+    return CopyElements(from_holder, 0, to, to_kind, 0, -1, from);
+  }
+
   virtual MaybeObject* AddElementsToFixedArray(Object* receiver,
                                                JSObject* holder,
                                                FixedArray* to,
@@ -123,6 +145,17 @@ class ElementsAccessor {
   DISALLOW_COPY_AND_ASSIGN(ElementsAccessor);
 };
 
+
+void CopyObjectToObjectElements(AssertNoAllocation* no_gc,
+                                FixedArray* from_obj,
+                                ElementsKind from_kind,
+                                uint32_t from_start,
+                                FixedArray* to_obj,
+                                ElementsKind to_kind,
+                                uint32_t to_start,
+                                int copy_size);
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_ELEMENTS_H_

src/objects.cc

@@ -8456,43 +8456,6 @@ void Code::Disassemble(const char* name, FILE* out) {
 #endif  // ENABLE_DISASSEMBLER
 
 
-static void CopyFastElementsToFast(FixedArray* source,
-                                   FixedArray* destination,
-                                   WriteBarrierMode mode) {
-  int count = source->length();
-  int copy_size = Min(count, destination->length());
-  if (mode == SKIP_WRITE_BARRIER ||
-      !Page::FromAddress(destination->address())->IsFlagSet(
-          MemoryChunk::POINTERS_FROM_HERE_ARE_INTERESTING)) {
-    Address to = destination->address() + FixedArray::kHeaderSize;
-    Address from = source->address() + FixedArray::kHeaderSize;
-    memcpy(reinterpret_cast<void*>(to),
-           reinterpret_cast<void*>(from),
-           kPointerSize * copy_size);
-  } else {
-    for (int i = 0; i < copy_size; ++i) {
-      destination->set(i, source->get(i), mode);
-    }
-  }
-}
-
-
-static void CopySlowElementsToFast(SeededNumberDictionary* source,
-                                   FixedArray* destination,
-                                   WriteBarrierMode mode) {
-  int destination_length = destination->length();
-  for (int i = 0; i < source->Capacity(); ++i) {
-    Object* key = source->KeyAt(i);
-    if (key->IsNumber()) {
-      uint32_t entry = static_cast<uint32_t>(key->Number());
-      if (entry < static_cast<uint32_t>(destination_length)) {
-        destination->set(entry, source->ValueAt(i), mode);
-      }
-    }
-  }
-}
-
-
 MaybeObject* JSObject::SetFastElementsCapacityAndLength(
     int capacity,
     int length,
@@ -8526,79 +8489,17 @@ MaybeObject* JSObject::SetFastElementsCapacityAndLength(
 
   FixedArrayBase* old_elements_raw = elements();
   ElementsKind elements_kind = GetElementsKind();
-  switch (elements_kind) {
-    case FAST_SMI_ONLY_ELEMENTS:
-    case FAST_ELEMENTS: {
-      AssertNoAllocation no_gc;
-      WriteBarrierMode mode(new_elements->GetWriteBarrierMode(no_gc));
-      CopyFastElementsToFast(FixedArray::cast(old_elements_raw),
-                             new_elements, mode);
-      set_map_and_elements(new_map, new_elements);
-      break;
-    }
-    case DICTIONARY_ELEMENTS: {
-      AssertNoAllocation no_gc;
-      WriteBarrierMode mode = new_elements->GetWriteBarrierMode(no_gc);
-      CopySlowElementsToFast(SeededNumberDictionary::cast(old_elements_raw),
-                             new_elements,
-                             mode);
+  ElementsAccessor* accessor = ElementsAccessor::ForKind(elements_kind);
+  ElementsKind to_kind = (elements_kind == FAST_SMI_ONLY_ELEMENTS)
+      ? FAST_SMI_ONLY_ELEMENTS
+      : FAST_ELEMENTS;
+  //  int copy_size = Min(old_elements_raw->length(), new_elements->length());
+  accessor->CopyElements(this, new_elements, to_kind);
+  if (elements_kind != NON_STRICT_ARGUMENTS_ELEMENTS) {
     set_map_and_elements(new_map, new_elements);
-      break;
-    }
-    case NON_STRICT_ARGUMENTS_ELEMENTS: {
-      AssertNoAllocation no_gc;
-      WriteBarrierMode mode = new_elements->GetWriteBarrierMode(no_gc);
-      // The object's map and the parameter map are unchanged, the unaliased
-      // arguments are copied to the new backing store.
-      FixedArray* parameter_map = FixedArray::cast(old_elements_raw);
-      FixedArray* arguments = FixedArray::cast(parameter_map->get(1));
-      if (arguments->IsDictionary()) {
-        CopySlowElementsToFast(SeededNumberDictionary::cast(arguments),
-                               new_elements,
-                               mode);
   } else {
-        CopyFastElementsToFast(arguments, new_elements, mode);
-      }
+    FixedArray* parameter_map = FixedArray::cast(old_elements_raw);
     parameter_map->set(1, new_elements);
-      break;
-    }
-    case FAST_DOUBLE_ELEMENTS: {
-      FixedDoubleArray* old_elements = FixedDoubleArray::cast(old_elements_raw);
-      uint32_t old_length = static_cast<uint32_t>(old_elements->length());
-      // Fill out the new array with this content and array holes.
-      for (uint32_t i = 0; i < old_length; i++) {
-        if (!old_elements->is_the_hole(i)) {
-          Object* obj;
-          // Objects must be allocated in the old object space, since the
-          // overall number of HeapNumbers needed for the conversion might
-          // exceed the capacity of new space, and we would fail repeatedly
-          // trying to convert the FixedDoubleArray.
-          MaybeObject* maybe_value_object =
-              GetHeap()->AllocateHeapNumber(old_elements->get_scalar(i),
-                                            TENURED);
-          if (!maybe_value_object->To(&obj)) return maybe_value_object;
-          // Force write barrier. It's not worth trying to exploit
-          // elems->GetWriteBarrierMode(), since it requires an
-          // AssertNoAllocation stack object that would have to be positioned
-          // after the HeapNumber allocation anyway.
-          new_elements->set(i, obj, UPDATE_WRITE_BARRIER);
-        }
-      }
-      set_map(new_map);
-      set_elements(new_elements);
-      break;
-    }
-    case EXTERNAL_BYTE_ELEMENTS:
-    case EXTERNAL_UNSIGNED_BYTE_ELEMENTS:
-    case EXTERNAL_SHORT_ELEMENTS:
-    case EXTERNAL_UNSIGNED_SHORT_ELEMENTS:
-    case EXTERNAL_INT_ELEMENTS:
-    case EXTERNAL_UNSIGNED_INT_ELEMENTS:
-    case EXTERNAL_FLOAT_ELEMENTS:
-    case EXTERNAL_DOUBLE_ELEMENTS:
-    case EXTERNAL_PIXEL_ELEMENTS:
-      UNREACHABLE();
-      break;
   }
 
   if (FLAG_trace_elements_transitions) {