Reduce space usage of simple transitions and descriptors holders.

src/transitions.cc

Index: src/transitions.cc
diff --git a/src/transitions.cc b/src/transitions.cc
index 199fcc2c9838fb0691bbedd4c00e1dd7bd27bb3e..7233f7346e1a7239b3aee241c9b47d596d34a7a5 100644
--- a/src/transitions.cc
+++ b/src/transitions.cc
@@ -35,8 +35,8 @@ namespace v8 {
 namespace internal {
 
 
-MaybeObject* TransitionArray::Allocate(int number_of_transitions,
-                                       JSGlobalPropertyCell* descriptors_cell) {
+static MaybeObject* AllocateRaw(int length,
+                                JSGlobalPropertyCell* descriptors_cell) {
   Heap* heap = Isolate::Current()->heap();
 
   if (descriptors_cell == NULL) {
@@ -45,13 +45,22 @@ MaybeObject* TransitionArray::Allocate(int number_of_transitions,
     if (!maybe_cell->To(&descriptors_cell)) return maybe_cell;
   }
 
-  // Use FixedArray to not use DescriptorArray::cast on incomplete object.
+  // Use FixedArray to not use TransitionArray::cast on incomplete object.
   FixedArray* array;
-  MaybeObject* maybe_array =
-      heap->AllocateFixedArray(ToKeyIndex(number_of_transitions));
+  MaybeObject* maybe_array = heap->AllocateFixedArray(length);
   if (!maybe_array->To(&array)) return maybe_array;
 
-  array->set(kDescriptorsPointerIndex, descriptors_cell);
+  array->set(TransitionArray::kDescriptorsPointerIndex, descriptors_cell);
+  return array;
+}
+
+
+MaybeObject* TransitionArray::Allocate(int number_of_transitions,
+                                       JSGlobalPropertyCell* descriptors_cell) {
+  FixedArray* array;
+  MaybeObject* maybe_array =
+      AllocateRaw(ToKeyIndex(number_of_transitions), descriptors_cell);
+  if (!maybe_array->To(&array)) return maybe_array;
   array->set(kElementsTransitionIndex, Smi::FromInt(0));
   array->set(kPrototypeTransitionsIndex, Smi::FromInt(0));
   return array;
@@ -72,18 +81,46 @@ static bool InsertionPointFound(String* key1, String* key2) {
 }
 
 
-MaybeObject* TransitionArray::NewWith(
-    String* name,
-    Map* target,
-    JSGlobalPropertyCell* descriptors_pointer,
-    Object* back_pointer) {
+MaybeObject* TransitionArray::NewWith(SimpleTransitionFlag flag,
+                                      String* key,
+                                      Map* target,
+                                      JSGlobalPropertyCell* descriptors_pointer,
+                                      Object* back_pointer) {
+  TransitionArray* result;
+  MaybeObject* maybe_result;
+
+  if (flag == SIMPLE_TRANSITION) {
+    maybe_result = AllocateRaw(kSimpleTransitionSize, descriptors_pointer);
+    if (!maybe_result->To(&result)) return maybe_result;
+    result->set(kSimpleTransitionTarget, target);
+  } else {
+    maybe_result = Allocate(1, descriptors_pointer);
+    if (!maybe_result->To(&result)) return maybe_result;
+    result->NoIncrementalWriteBarrierSet(0, key, target);
+  }
+  result->set_back_pointer_storage(back_pointer);
+  return result;
+}
+
+
+MaybeObject* TransitionArray::AllocateDescriptorsHolder(
+    JSGlobalPropertyCell* descriptors_pointer) {
+  return AllocateRaw(kDescriptorsHolderSize, descriptors_pointer);
+}
+
+
+MaybeObject* TransitionArray::ExtendToFullTransitionArray() {
+  ASSERT(!IsFullTransitionArray());
+  int nof = number_of_transitions();
   TransitionArray* result;
+  MaybeObject* maybe_result = Allocate(nof, descriptors_pointer());
+  if (!maybe_result->To(&result)) return maybe_result;
 
-  MaybeObject* maybe_array = TransitionArray::Allocate(1, descriptors_pointer);
-  if (!maybe_array->To(&result)) return maybe_array;
+  if (nof == 1) {
+    result->NoIncrementalWriteBarrierCopyFrom(this, kSimpleTransitionIndex, 0);
+  }
 
-  result->NoIncrementalWriteBarrierSet(0, name, target);
-  result->set_back_pointer_storage(back_pointer);
+  result->set_back_pointer_storage(back_pointer_storage());
   return result;
 }