[IMP] core: speed up loading of registry

The base classes of models in the registry are modified when models are
extended by inheritance.  But modifying cls.__bases__ is a costly
operation, so we manage to do it once per model when loading a registry.

Our benchmark consists in loading a registry with 296 modules.  The net
time to load the registry is 25% smaller.  In other words, the registry
loads 25% faster.  Note that the time does not include the time to load
modules themselves, which does not change.

odoo/addons/test_new_api/tests/test_new_fields.py

@@ -3086,7 +3086,7 @@ class TestSelectionOndeleteAdvanced(common.TransactionCase):
         # necessary cleanup for resetting changes in the registry
         for model_name in (self.MODEL_BASE, self.MODEL_REQUIRED):
             Model = self.registry[model_name]
-            self.addCleanup(setattr, Model, '__bases__', Model.__bases__)
+            self.addCleanup(setattr, Model, '_BaseModel__base_classes', Model._BaseModel__base_classes)
 
     def test_ondelete_unexisting_policy(self):
         class Foo(models.Model):

odoo/models.py

@@ -618,7 +618,7 @@ class BaseModel(metaclass=MetaModel):
             ModelClass._build_model_check_base(cls)
             check_parent = ModelClass._build_model_check_parent
         else:
-            ModelClass = type(name, (BaseModel,), {
+            ModelClass = type(name, (cls,), {
                 '_name': name,
                 '_register': False,
                 '_original_module': cls._module,
@@ -636,7 +636,7 @@ class BaseModel(metaclass=MetaModel):
                 raise TypeError("Model %r inherits from non-existing model %r." % (name, parent))
             parent_class = pool[parent]
             if parent == name:
-                for base in parent_class.__bases__:
+                for base in parent_class.__base_classes:
                     bases.add(base)
             else:
                 check_parent(cls, parent_class)
@@ -644,7 +644,9 @@ class BaseModel(metaclass=MetaModel):
                 ModelClass._inherit_module[parent] = cls._module
                 parent_class._inherit_children.add(name)
 
-        ModelClass.__bases__ = tuple(bases)
+        # ModelClass.__bases__ must be assigned those classes; however, this
+        # operation is quite slow, so we do it once in method _prepare_setup()
+        ModelClass.__base_classes = tuple(bases)
 
         # determine the attributes of the model's class
         ModelClass._build_model_attributes(pool)
@@ -701,7 +703,7 @@ class BaseModel(metaclass=MetaModel):
         cls._depends = {}
         cls._sql_constraints = {}
 
-        for base in reversed(cls.__bases__):
+        for base in reversed(cls.__base_classes):
             if is_definition_class(base):
                 # the following attributes are not taken from registry classes
                 if cls._name not in base._inherit and not base._description:
@@ -2839,6 +2841,10 @@ class BaseModel(metaclass=MetaModel):
         cls = type(self)
         cls._setup_done = False
 
+        # changing base classes is costly, do it only when necessary
+        if cls.__bases__ != cls.__base_classes:
+            cls.__bases__ = cls.__base_classes
+
         # reset those attributes on the model's class for _setup_fields() below
         for attr in ('_rec_name', '_active_name'):
             discardattr(cls, attr)