Grouping all map creation code.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index f672534791d9277fe0d4990a896428bdfca81ef7..0844c1d02bfcc4019bc3da1fe3d99aeb8186aadd 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -1293,14 +1293,12 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_DisableAccessChecks) {
   bool needs_access_checks = old_map->is_access_check_needed();
   if (needs_access_checks) {
     // Copy map so it won't interfere constructor's initial map.
-    Object* new_map;
-    { MaybeObject* maybe_new_map =
-          old_map->CopyDropTransitions(DescriptorArray::MAY_BE_SHARED);
-      if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
-    }
+    Map* new_map;
+    MaybeObject* maybe_new_map = old_map->Copy(DescriptorArray::MAY_BE_SHARED);
+    if (!maybe_new_map->To(&new_map)) return maybe_new_map;
 
-    Map::cast(new_map)->set_is_access_check_needed(false);
-    object->set_map(Map::cast(new_map));
+    new_map->set_is_access_check_needed(false);
+    object->set_map(new_map);
   }
   return isolate->heap()->ToBoolean(needs_access_checks);
 }
@@ -1312,14 +1310,12 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_EnableAccessChecks) {
   Map* old_map = object->map();
   if (!old_map->is_access_check_needed()) {
     // Copy map so it won't interfere constructor's initial map.
-    Object* new_map;
-    { MaybeObject* maybe_new_map =
-          old_map->CopyDropTransitions(DescriptorArray::MAY_BE_SHARED);
-      if (!maybe_new_map->ToObject(&new_map)) return maybe_new_map;
-    }
+    Map* new_map;
+    MaybeObject* maybe_new_map = old_map->Copy(DescriptorArray::MAY_BE_SHARED);
+    if (!maybe_new_map->To(&new_map)) return maybe_new_map;
 
-    Map::cast(new_map)->set_is_access_check_needed(true);
-    object->set_map(Map::cast(new_map));
+    new_map->set_is_access_check_needed(true);
+    object->set_map(new_map);
   }
   return isolate->heap()->undefined_value();
 }
@@ -2172,25 +2168,24 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_FunctionSetReadOnlyPrototype) {
   if (function->HasFastProperties()) {
     // Construct a new field descriptor with updated attributes.
     DescriptorArray* instance_desc = function->map()->instance_descriptors();
+
     int index = instance_desc->Search(name);
     ASSERT(index != DescriptorArray::kNotFound);
     PropertyDetails details = instance_desc->GetDetails(index);
+
     CallbacksDescriptor new_desc(name,
         instance_desc->GetValue(index),
         static_cast<PropertyAttributes>(details.attributes() | READ_ONLY),
         details.index());
-    // Construct a new field descriptors array containing the new descriptor.
-    DescriptorArray* new_descriptors;
-    { MaybeObject* maybe_descriptors =
-          instance_desc->CopyReplace(&new_desc, index);
-      if (!maybe_descriptors->To(&new_descriptors)) return maybe_descriptors;
-    }
+
     // Create a new map featuring the new field descriptors array.
     Map* new_map;
-    { MaybeObject* maybe_map =
-          function->map()->CopyReplaceDescriptors(new_descriptors);
-      if (!maybe_map->To(&new_map)) return maybe_map;
-    }
+    MaybeObject* maybe_map =
+        function->map()->CopyReplaceDescriptor(&new_desc,

[Jakob Kummerow, 2012/07/17 13:43:10]

nit: if you want, you can save one line here as follows:
MaybeObject* maybe_map =
    function->map()->CopyReplaceDescriptor(
        &new_desc, index, OMIT_TRANSITION);
but I don't feel strongly about it either way. Choose whatever you find is more
readable.

+                                               index,
+                                               OMIT_TRANSITION);
+    if (!maybe_map->To(&new_map)) return maybe_map;
+
     function->set_map(new_map);
   } else {  // Dictionary properties.
     // Directly manipulate the property details.
@@ -7829,8 +7824,7 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_NewArgumentsFast) {
           isolate->heap()->non_strict_arguments_elements_map());
 
       Handle<Map> old_map(result->map());
-      Handle<Map> new_map =
-          isolate->factory()->CopyMapDropTransitions(old_map);
+      Handle<Map> new_map = isolate->factory()->CopyMap(old_map);
       new_map->set_elements_kind(NON_STRICT_ARGUMENTS_ELEMENTS);
 
       result->set_map(*new_map);