Fix and cleanup Map::GeneralizeRepresentation().

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 98e043671175e6e1f3708d478fa651ae4ac89842..21ed836cce1a21af3dace2c0cee605fb95db818d 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2425,43 +2425,6 @@ Map* Map::FindRootMap() {
 }
 
 
-// Returns NULL if the updated map is incompatible.
-Map* Map::FindUpdatedMap(int verbatim,
-                         int length,
-                         DescriptorArray* descriptors) {
-  DisallowHeapAllocation no_allocation;
-
-  // This can only be called on roots of transition trees.
-  ASSERT(GetBackPointer()->IsUndefined());
-
-  Map* current = this;
-
-  for (int i = verbatim; i < length; i++) {
-    if (!current->HasTransitionArray()) break;
-    Name* name = descriptors->GetKey(i);
-    TransitionArray* transitions = current->transitions();
-    int transition = transitions->Search(name);
-    if (transition == TransitionArray::kNotFound) break;
-    current = transitions->GetTarget(transition);
-    PropertyDetails details = descriptors->GetDetails(i);
-    PropertyDetails target_details =
-        current->instance_descriptors()->GetDetails(i);
-    if (details.attributes() != target_details.attributes()) return NULL;
-    if (details.type() == CALLBACKS) {
-      if (target_details.type() != CALLBACKS) return NULL;
-      if (descriptors->GetValue(i) !=
-              current->instance_descriptors()->GetValue(i)) {
-        return NULL;
-      }
-    } else if (target_details.type() == CALLBACKS) {
-      return NULL;
-    }
-  }
-
-  return current;
-}
-
-
 Map* Map::FindLastMatchMap(int verbatim,
                            int length,
                            DescriptorArray* descriptors) {
@@ -2552,13 +2515,10 @@ void Map::GeneralizeFieldType(Handle<Map> map,
                               int modify_index,
                               Handle<HeapType> new_field_type) {
   Isolate* isolate = map->GetIsolate();
-  Handle<Map> field_owner(map->FindFieldOwner(modify_index), isolate);
-  Handle<DescriptorArray> descriptors(
-      field_owner->instance_descriptors(), isolate);
 
   // Check if we actually need to generalize the field type at all.
   Handle<HeapType> old_field_type(
-      descriptors->GetFieldType(modify_index), isolate);
+      map->instance_descriptors()->GetFieldType(modify_index), isolate);
   if (new_field_type->NowIs(old_field_type)) {
     ASSERT(Map::GeneralizeFieldType(old_field_type,
                                     new_field_type,
@@ -2566,6 +2526,12 @@ void Map::GeneralizeFieldType(Handle<Map> map,
     return;
   }
 
+  // Determine the field owner.
+  Handle<Map> field_owner(map->FindFieldOwner(modify_index), isolate);
+  Handle<DescriptorArray> descriptors(
+      field_owner->instance_descriptors(), isolate);
+  ASSERT_EQ(*old_field_type, descriptors->GetFieldType(modify_index));
+
   // Determine the generalized new field type.
   new_field_type = Map::GeneralizeFieldType(
       old_field_type, new_field_type, isolate);
@@ -2598,23 +2564,28 @@ void Map::GeneralizeFieldType(Handle<Map> map,
 // (partial) version of the type in the transition tree.
 // To do this, on each rewrite:
 // - Search the root of the transition tree using FindRootMap.
-// - Find |updated|, the newest matching version of this map using
-//   FindUpdatedMap. This uses the keys in the own map's descriptor array to
-//   walk the transition tree.
-// - Merge/generalize the descriptor array of the current map and |updated|.
-// - Generalize the |modify_index| descriptor using |new_representation|.
-// - Walk the tree again starting from the root towards |updated|. Stop at
+// - Find |target_map|, the newest matching version of this map using the keys
+//   in the |old_map|'s descriptor array to walk the transition tree.
+// - Merge/generalize the descriptor array of the |old_map| and |target_map|.
+// - Generalize the |modify_index| descriptor using |new_representation| and
+//   |new_field_type|.
+// - Walk the tree again starting from the root towards |target_map|. Stop at
 //   |split_map|, the first map who's descriptor array does not match the merged
 //   descriptor array.
-// - If |updated| == |split_map|, |updated| is in the expected state. Return it.
-// - Otherwise, invalidate the outdated transition target from |updated|, and
+// - If |target_map| == |split_map|, |target_map| is in the expected state.
+//   Return it.
+// - Otherwise, invalidate the outdated transition target from |target_map|, and
 //   replace its transition tree with a new branch for the updated descriptors.
 Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
                                           int modify_index,
                                           Representation new_representation,
                                           Handle<HeapType> new_field_type,
                                           StoreMode store_mode) {
-  Handle<DescriptorArray> old_descriptors(old_map->instance_descriptors());
+  Isolate* isolate = old_map->GetIsolate();
+
+  Handle<DescriptorArray> old_descriptors(
+      old_map->instance_descriptors(), isolate);
+  int old_nof = old_map->NumberOfOwnDescriptors();
   PropertyDetails old_details = old_descriptors->GetDetails(modify_index);
   Representation old_representation = old_details.representation();
 
@@ -2641,84 +2612,239 @@ Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
     return old_map;
   }
 
-  if (new_representation.Equals(old_representation) &&
-      old_details.type() == FIELD) {
-    Map::GeneralizeFieldType(old_map, modify_index, new_field_type);
-    return old_map;
-  }
-
-  Handle<Map> root_map(old_map->FindRootMap());
-
   // Check the state of the root map.
+  Handle<Map> root_map(old_map->FindRootMap(), isolate);
   if (!old_map->EquivalentToForTransition(*root_map)) {
     return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
         old_details.attributes(), "not equivalent");
   }
+  int root_nof = root_map->NumberOfOwnDescriptors();
+  if (modify_index < root_nof) {
+    PropertyDetails old_details = old_descriptors->GetDetails(modify_index);
+    if ((old_details.type() != FIELD && store_mode == FORCE_FIELD) ||
+        (old_details.type() == FIELD &&
+         (!new_field_type->NowIs(old_descriptors->GetFieldType(modify_index)) ||
+          !new_representation.fits_into(old_details.representation())))) {
+      return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
+          old_details.attributes(), "root modification");
+    }
+  }
 
-  int verbatim = root_map->NumberOfOwnDescriptors();
+  Handle<Map> target_map = root_map;
+  for (int i = root_nof; i < old_nof; ++i) {
+    int j = target_map->SearchTransition(old_descriptors->GetKey(i));
+    if (j == TransitionArray::kNotFound) break;
+    Handle<Map> tmp_map(target_map->GetTransition(j), isolate);
+    Handle<DescriptorArray> tmp_descriptors = handle(
+        tmp_map->instance_descriptors(), isolate);
 
-  if (store_mode != ALLOW_AS_CONSTANT && modify_index < verbatim) {
-    return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
-        old_details.attributes(), "root modification");
+    // Check if target map is incompatible.
+    PropertyDetails old_details = old_descriptors->GetDetails(i);
+    PropertyDetails tmp_details = tmp_descriptors->GetDetails(i);
+    PropertyType old_type = old_details.type();
+    PropertyType tmp_type = tmp_details.type();
+    if (tmp_details.attributes() != old_details.attributes() ||
+        ((tmp_type == CALLBACKS || old_type == CALLBACKS) &&
+         (tmp_type != old_type ||
+          tmp_descriptors->GetValue(i) != old_descriptors->GetValue(i)))) {
+      return CopyGeneralizeAllRepresentations(
+          old_map, modify_index, store_mode,
+          old_details.attributes(), "incompatible");
+    }
+    Representation old_representation = old_details.representation();
+    Representation tmp_representation = tmp_details.representation();
+    if (!old_representation.fits_into(tmp_representation) ||
+        (!new_representation.fits_into(tmp_representation) &&
+         modify_index == i)) {
+      break;
+    }
+    if (tmp_type == FIELD) {
+      // Generalize the field type as necessary.
+      Handle<HeapType> old_field_type = (old_type == FIELD)
+          ? handle(old_descriptors->GetFieldType(i), isolate)
+          : old_descriptors->GetValue(i)->OptimalType(
+              isolate, tmp_representation);
+      if (modify_index == i) {
+        old_field_type = GeneralizeFieldType(
+            new_field_type, old_field_type, isolate);
+      }
+      GeneralizeFieldType(tmp_map, i, old_field_type);
+    } else if (tmp_type == CONSTANT) {
+      if (old_type != CONSTANT ||
+          old_descriptors->GetConstant(i) != tmp_descriptors->GetConstant(i)) {
+        break;
+      }
+    } else {
+      ASSERT_EQ(tmp_type, old_type);
+      ASSERT_EQ(tmp_descriptors->GetValue(i), old_descriptors->GetValue(i));
+    }
+    target_map = tmp_map;
+  }
+
+  // Directly change the map if the target map is more general.
+  Handle<DescriptorArray> target_descriptors(
+      target_map->instance_descriptors(), isolate);
+  int target_nof = target_map->NumberOfOwnDescriptors();
+  if (target_nof == old_nof &&
+      (store_mode != FORCE_FIELD ||
+       target_descriptors->GetDetails(modify_index).type() == FIELD)) {
+    ASSERT(modify_index < target_nof);
+    ASSERT(new_representation.fits_into(
+            target_descriptors->GetDetails(modify_index).representation()));
+    ASSERT(target_descriptors->GetDetails(modify_index).type() != FIELD ||
+           new_field_type->NowIs(
+               target_descriptors->GetFieldType(modify_index)));
+    return target_map;
+  }
+
+  // Find the last compatible target map in the transition tree.
+  for (int i = target_nof; i < old_nof; ++i) {
+    int j = target_map->SearchTransition(old_descriptors->GetKey(i));
+    if (j == TransitionArray::kNotFound) break;
+    Handle<Map> tmp_map(target_map->GetTransition(j), isolate);
+    Handle<DescriptorArray> tmp_descriptors(
+        tmp_map->instance_descriptors(), isolate);
+
+    // Check if target map is compatible.
+    PropertyDetails old_details = old_descriptors->GetDetails(i);
+    PropertyDetails tmp_details = tmp_descriptors->GetDetails(i);
+    if (tmp_details.attributes() != old_details.attributes() ||
+        ((tmp_details.type() == CALLBACKS || old_details.type() == CALLBACKS) &&
+         (tmp_details.type() != old_details.type() ||
+          tmp_descriptors->GetValue(i) != old_descriptors->GetValue(i)))) {
+      return CopyGeneralizeAllRepresentations(
+          old_map, modify_index, store_mode,
+          old_details.attributes(), "incompatible");
+    }
+    target_map = tmp_map;
   }
+  target_nof = target_map->NumberOfOwnDescriptors();
+  target_descriptors = handle(target_map->instance_descriptors(), isolate);
 
-  int descriptors = old_map->NumberOfOwnDescriptors();
-  Map* raw_updated = root_map->FindUpdatedMap(
-      verbatim, descriptors, *old_descriptors);
-  if (raw_updated == NULL) {
-    return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
-        old_details.attributes(), "incompatible");
+  // Allocate a new descriptor array large enough to hold the required
+  // descriptors, with minimally the exact same size as the old descriptor
+  // array.
+  int new_slack = Max(
+      old_nof, old_descriptors->number_of_descriptors()) - old_nof;
+  Handle<DescriptorArray> new_descriptors = DescriptorArray::Allocate(
+      isolate, old_nof, new_slack);
+  ASSERT(new_descriptors->length() > target_descriptors->length() ||
+         new_descriptors->NumberOfSlackDescriptors() > 0 ||
+         new_descriptors->number_of_descriptors() ==
+         old_descriptors->number_of_descriptors());
+  ASSERT(new_descriptors->number_of_descriptors() == old_nof);
+
+  // 0 -> |root_nof|
+  int current_offset = 0;
+  for (int i = 0; i < root_nof; ++i) {
+    PropertyDetails old_details = old_descriptors->GetDetails(i);
+    if (old_details.type() == FIELD) current_offset++;
+    Descriptor d(handle(old_descriptors->GetKey(i), isolate),
+                 handle(old_descriptors->GetValue(i), isolate),
+                 old_details);
+    new_descriptors->Set(i, &d);
   }
 
-  Handle<Map> updated(raw_updated);
-  Handle<DescriptorArray> updated_descriptors(updated->instance_descriptors());
-
-  int valid = updated->NumberOfOwnDescriptors();
+  // |root_nof| -> |target_nof|
+  for (int i = root_nof; i < target_nof; ++i) {
+    Handle<Name> target_key(target_descriptors->GetKey(i), isolate);
+    PropertyDetails old_details = old_descriptors->GetDetails(i);
+    PropertyDetails target_details = target_descriptors->GetDetails(i);
+    target_details = target_details.CopyWithRepresentation(
+        old_details.representation().generalize(
+            target_details.representation()));
+    if (modify_index == i) {
+      target_details = target_details.CopyWithRepresentation(
+          new_representation.generalize(target_details.representation()));
+    }
+    if (old_details.type() == FIELD ||
+        target_details.type() == FIELD ||
+        (modify_index == i && store_mode == FORCE_FIELD) ||
+        (target_descriptors->GetValue(i) != old_descriptors->GetValue(i))) {
+      Handle<HeapType> old_field_type = (old_details.type() == FIELD)
+          ? handle(old_descriptors->GetFieldType(i), isolate)
+          : old_descriptors->GetValue(i)->OptimalType(
+              isolate, target_details.representation());
+      Handle<HeapType> target_field_type = (target_details.type() == FIELD)
+          ? handle(target_descriptors->GetFieldType(i), isolate)
+          : target_descriptors->GetValue(i)->OptimalType(
+              isolate, target_details.representation());
+      target_field_type = GeneralizeFieldType(
+          target_field_type, old_field_type, isolate);
+      if (modify_index == i) {
+        target_field_type = GeneralizeFieldType(
+            target_field_type, new_field_type, isolate);
+      }
+      FieldDescriptor d(target_key,
+                        current_offset++,
+                        target_field_type,
+                        target_details.attributes(),
+                        target_details.representation());
+      new_descriptors->Set(i, &d);
+    } else {
+      ASSERT_NE(FIELD, target_details.type());
+      Descriptor d(target_key,
+                   handle(target_descriptors->GetValue(i), isolate),
+                   target_details);
+      new_descriptors->Set(i, &d);
+    }
+  }
 
-  // Directly change the map if the target map is more general. Ensure that the
-  // target type of the modify_index is a FIELD, unless we are migrating.
-  if (updated_descriptors->IsMoreGeneralThan(
-          verbatim, valid, descriptors, *old_descriptors) &&
-      (store_mode == ALLOW_AS_CONSTANT ||
-       updated_descriptors->GetDetails(modify_index).type() == FIELD)) {
-    Representation updated_representation =
-        updated_descriptors->GetDetails(modify_index).representation();
-    if (new_representation.fits_into(updated_representation)) return updated;
+  // |target_nof| -> |old_nof|
+  for (int i = target_nof; i < old_nof; ++i) {
+    PropertyDetails old_details = old_descriptors->GetDetails(i);
+    Handle<Name> old_key(old_descriptors->GetKey(i), isolate);
+    if (modify_index == i) {
+      old_details = old_details.CopyWithRepresentation(
+          new_representation.generalize(old_details.representation()));
+    }
+    if (old_details.type() == FIELD) {
+      Handle<HeapType> old_field_type(
+          old_descriptors->GetFieldType(i), isolate);
+      if (modify_index == i) {
+        old_field_type = GeneralizeFieldType(
+            old_field_type, new_field_type, isolate);
+      }
+      FieldDescriptor d(old_key,
+                        current_offset++,
+                        old_field_type,
+                        old_details.attributes(),
+                        old_details.representation());
+      new_descriptors->Set(i, &d);
+    } else {
+      ASSERT(old_details.type() == CONSTANT || old_details.type() == CALLBACKS);
+      if (modify_index == i && store_mode == FORCE_FIELD) {
+        FieldDescriptor d(old_key,
+                          current_offset++,
+                          GeneralizeFieldType(
+                              old_descriptors->GetValue(i)->OptimalType(
+                                  isolate, old_details.representation()),
+                              new_field_type, isolate),
+                          old_details.attributes(),
+                          old_details.representation());
+        new_descriptors->Set(i, &d);
+      } else {
+        ASSERT_NE(FIELD, old_details.type());
+        Descriptor d(old_key,
+                     handle(old_descriptors->GetValue(i), isolate),
+                     old_details);
+        new_descriptors->Set(i, &d);
+      }
+    }
   }
 
-  Handle<DescriptorArray> new_descriptors = DescriptorArray::Merge(
-      updated, verbatim, valid, descriptors, modify_index,
-      store_mode, old_map);
-  ASSERT(store_mode == ALLOW_AS_CONSTANT ||
-         new_descriptors->GetDetails(modify_index).type() == FIELD);
+  new_descriptors->Sort();
 
-  Isolate* isolate = new_descriptors->GetIsolate();
-  old_representation =
-      new_descriptors->GetDetails(modify_index).representation();
-  Representation updated_representation =
-      new_representation.generalize(old_representation);
-  if (!updated_representation.Equals(old_representation)) {
-    new_descriptors->SetRepresentation(modify_index, updated_representation);
-  }
-  if (new_descriptors->GetDetails(modify_index).type() == FIELD) {
-    Handle<HeapType> field_type(
-        new_descriptors->GetFieldType(modify_index), isolate);
-    new_field_type = Map::GeneralizeFieldType(
-        field_type, new_field_type, isolate);
-    new_descriptors->SetValue(modify_index, *new_field_type);
-  }
+  ASSERT(store_mode != FORCE_FIELD ||
+         new_descriptors->GetDetails(modify_index).type() == FIELD);
 
   Handle<Map> split_map(root_map->FindLastMatchMap(
-      verbatim, descriptors, *new_descriptors));
+          root_nof, old_nof, *new_descriptors), isolate);
+  int split_nof = split_map->NumberOfOwnDescriptors();
+  ASSERT_NE(old_nof, split_nof);
 
-  int split_descriptors = split_map->NumberOfOwnDescriptors();
-  // This is shadowed by |updated_descriptors| being more general than
-  // |old_descriptors|.
-  ASSERT(descriptors != split_descriptors);
-
-  int descriptor = split_descriptors;
   split_map->DeprecateTarget(
-      old_descriptors->GetKey(descriptor), *new_descriptors);
+      old_descriptors->GetKey(split_nof), *new_descriptors);
 
   if (FLAG_trace_generalization) {
     PropertyDetails old_details = old_descriptors->GetDetails(modify_index);
@@ -2732,7 +2858,7 @@ Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
         : HeapType::Constant(handle(new_descriptors->GetValue(modify_index),
                                     isolate), isolate);
     old_map->PrintGeneralization(
-        stdout, "", modify_index, descriptor, descriptors,
+        stdout, "", modify_index, split_nof, old_nof,
         old_details.type() == CONSTANT && store_mode == FORCE_FIELD,
         old_details.representation(), new_details.representation(),
         *old_field_type, *new_field_type);
@@ -2740,10 +2866,9 @@ Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
 
   // Add missing transitions.
   Handle<Map> new_map = split_map;
-  for (; descriptor < descriptors; descriptor++) {
-    new_map = CopyInstallDescriptors(new_map, descriptor, new_descriptors);
+  for (int i = split_nof; i < old_nof; ++i) {
+    new_map = CopyInstallDescriptors(new_map, i, new_descriptors);
   }
-
   new_map->set_owns_descriptors(true);
   return new_map;
 }
@@ -8397,150 +8522,6 @@ void DescriptorArray::CopyFrom(int index,
 }
 
 
-// Creates a new descriptor array by merging the descriptor array of |right_map|
-// into the (at least partly) updated descriptor array of |left_map|.
-// The method merges two descriptor array in three parts. Both descriptor arrays
-// are identical up to |verbatim|. They also overlap in keys up to |valid|.
-// Between |verbatim| and |valid|, the resulting descriptor type as well as the
-// representation are generalized from both |left_map| and |right_map|. Beyond
-// |valid|, the descriptors are copied verbatim from |right_map| up to
-// |new_size|.
-// In case of incompatible types, the type and representation of |right_map| is
-// used.
-Handle<DescriptorArray> DescriptorArray::Merge(Handle<Map> left_map,
-                                               int verbatim,
-                                               int valid,
-                                               int new_size,
-                                               int modify_index,
-                                               StoreMode store_mode,
-                                               Handle<Map> right_map) {
-  ASSERT(verbatim <= valid);
-  ASSERT(valid <= new_size);
-
-  // Allocate a new descriptor array large enough to hold the required
-  // descriptors, with minimally the exact same size as this descriptor array.
-  Isolate* isolate = left_map->GetIsolate();
-  Handle<DescriptorArray> left(left_map->instance_descriptors());
-  Handle<DescriptorArray> right(right_map->instance_descriptors());
-  Handle<DescriptorArray> result = DescriptorArray::Allocate(
-      isolate,
-      new_size,
-      Max(new_size, right->number_of_descriptors()) - new_size);
-  ASSERT(result->length() > left->length() ||
-         result->NumberOfSlackDescriptors() > 0 ||
-         result->number_of_descriptors() == right->number_of_descriptors());
-  ASSERT(result->number_of_descriptors() == new_size);
-
-  int descriptor;
-
-  // 0 -> |verbatim|
-  int current_offset = 0;
-  for (descriptor = 0; descriptor < verbatim; descriptor++) {
-    if (left->GetDetails(descriptor).type() == FIELD) current_offset++;
-    Descriptor d(handle(right->GetKey(descriptor)),
-                 handle(right->GetValue(descriptor), right->GetIsolate()),
-                 right->GetDetails(descriptor));
-    result->Set(descriptor, &d);
-  }
-
-  // |verbatim| -> |valid|
-  for (; descriptor < valid; descriptor++) {
-    PropertyDetails left_details = left->GetDetails(descriptor);
-    PropertyDetails right_details = right->GetDetails(descriptor);
-    if (left_details.type() == FIELD || right_details.type() == FIELD ||
-        (store_mode == FORCE_FIELD && descriptor == modify_index) ||
-        (left_details.type() == CONSTANT &&
-         right_details.type() == CONSTANT &&
-         left->GetValue(descriptor) != right->GetValue(descriptor))) {
-      ASSERT(left_details.type() == CONSTANT || left_details.type() == FIELD);
-      ASSERT(right_details.type() == CONSTANT || right_details.type() == FIELD);
-      Representation representation = left_details.representation().generalize(
-          right_details.representation());
-      Handle<HeapType> left_type = (left_details.type() == FIELD)
-          ? handle(left->GetFieldType(descriptor), isolate)
-          : left->GetValue(descriptor)->OptimalType(isolate, representation);
-      Handle<HeapType> right_type = (right_details.type() == FIELD)
-          ? handle(right->GetFieldType(descriptor), isolate)
-          : right->GetValue(descriptor)->OptimalType(isolate, representation);
-      Handle<HeapType> field_type = Map::GeneralizeFieldType(
-          left_type, right_type, isolate);
-      FieldDescriptor d(handle(left->GetKey(descriptor), isolate),
-                        current_offset++,
-                        field_type,
-                        right_details.attributes(),
-                        representation);
-      result->Set(descriptor, &d);
-    } else {
-      Descriptor d(handle(right->GetKey(descriptor), isolate),
-                   handle(right->GetValue(descriptor), isolate),
-                   right_details);
-      result->Set(descriptor, &d);
-    }
-  }
-
-  // |valid| -> |new_size|
-  for (; descriptor < new_size; descriptor++) {
-    PropertyDetails right_details = right->GetDetails(descriptor);
-    if (right_details.type() == FIELD) {
-      FieldDescriptor d(handle(right->GetKey(descriptor), isolate),
-                        current_offset++,
-                        handle(right->GetFieldType(descriptor), isolate),
-                        right_details.attributes(),
-                        right_details.representation());
-      result->Set(descriptor, &d);
-    } else if (store_mode == FORCE_FIELD && descriptor == modify_index) {
-      ASSERT_EQ(CONSTANT, right_details.type());
-      Representation field_representation = right_details.representation();
-      Handle<HeapType> field_type = right->GetValue(descriptor)->OptimalType(
-          isolate, field_representation);
-      FieldDescriptor d(handle(right->GetKey(descriptor), isolate),
-                        current_offset++,
-                        field_type,
-                        right_details.attributes(),
-                        field_representation);
-      result->Set(descriptor, &d);
-    } else {
-      Descriptor d(handle(right->GetKey(descriptor), isolate),
-                   handle(right->GetValue(descriptor), isolate),
-                   right_details);
-      result->Set(descriptor, &d);
-    }
-  }
-
-  result->Sort();
-  return result;
-}
-
-
-// Checks whether a merge of |other| into |this| would return a copy of |this|.
-bool DescriptorArray::IsMoreGeneralThan(int verbatim,
-                                        int valid,
-                                        int new_size,
-                                        DescriptorArray* other) {
-  ASSERT(verbatim <= valid);
-  ASSERT(valid <= new_size);
-  if (valid != new_size) return false;
-
-  for (int descriptor = verbatim; descriptor < valid; descriptor++) {
-    PropertyDetails details = GetDetails(descriptor);
-    PropertyDetails other_details = other->GetDetails(descriptor);
-    if (!other_details.representation().fits_into(details.representation())) {
-      return false;
-    }
-    if (details.type() == CONSTANT) {
-      if (other_details.type() != CONSTANT) return false;
-      if (GetValue(descriptor) != other->GetValue(descriptor)) return false;
-    } else if (details.type() == FIELD && other_details.type() == FIELD) {
-      if (!other->GetFieldType(descriptor)->NowIs(GetFieldType(descriptor))) {
-        return false;
-      }
-    }
-  }
-
-  return true;
-}
-
-
 // We need the whiteness witness since sort will reshuffle the entries in the
 // descriptor array. If the descriptor array were to be black, the shuffling
 // would move a slot that was already recorded as pointing into an evacuation