Variation of patch # 1624059 to speed up checking if an object is a subclass
of some of the common builtin types.
Use a bit in tp_flags for each common builtin type. Check the bit
to determine if any instance is a subclass of these common types.
The check avoids a function call and O(n) search of the base classes.
The check is done in the various Py*_Check macros rather than calling
PyType_IsSubtype().
All the bits are set in tp_flags when the type is declared
in the Objects/*object.c files because PyType_Ready() is not called
for all the types. Should PyType_Ready() be called for all types?
If so and the change is made, the changes to the Objects/*object.c files
can be reverted (remove setting the tp_flags). Objects/typeobject.c
would also have to be modified to add conditions
for Py*_CheckExact() in addition to each the PyType_IsSubtype check.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 290e8df..a49fe39 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -7967,7 +7967,7 @@
0, /* tp_setattro */
&unicode_as_buffer, /* tp_as_buffer */
Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES |
- Py_TPFLAGS_BASETYPE, /* tp_flags */
+ Py_TPFLAGS_BASETYPE | Py_TPFLAGS_UNICODE_SUBCLASS, /* tp_flags */
unicode_doc, /* tp_doc */
0, /* tp_traverse */
0, /* tp_clear */