bpo-46131: add fastpath for PyFloat_Check() (#30200)

Author: mattip

Doc/c-api/typeobj.rst

@@ -1145,6 +1145,7 @@ and :c:type:`PyType_Type` effectively act as defaults.)
    .. XXX Document more flags here?
 
 
+   .. data:: Py_TPFLAGS_FLOAT_SUBCLASS
    .. data:: Py_TPFLAGS_LONG_SUBCLASS
    .. data:: Py_TPFLAGS_LIST_SUBCLASS
    .. data:: Py_TPFLAGS_TUPLE_SUBCLASS

Include/floatobject.h

@@ -14,6 +14,8 @@ extern "C" {
 PyAPI_DATA(PyTypeObject) PyFloat_Type;
 
 #define PyFloat_Check(op) PyObject_TypeCheck(op, &PyFloat_Type)
+#define PyFloat_Check(op) \
+        PyType_FastSubclass(Py_TYPE(op), Py_TPFLAGS_FLOAT_SUBCLASS)
 #define PyFloat_CheckExact(op) Py_IS_TYPE(op, &PyFloat_Type)
 
 #ifdef Py_NAN

Include/object.h

@@ -397,6 +397,7 @@ given type object has a specified feature.
 #define _Py_TPFLAGS_MATCH_SELF (1UL << 22)
 
 /* These flags are used to determine if a type is a subclass. */
+#define Py_TPFLAGS_FLOAT_SUBCLASS       (1UL << 23)
 #define Py_TPFLAGS_LONG_SUBCLASS        (1UL << 24)
 #define Py_TPFLAGS_LIST_SUBCLASS        (1UL << 25)
 #define Py_TPFLAGS_TUPLE_SUBCLASS       (1UL << 26)

Misc/NEWS.d/next/C API/2021-12-19-13-02-59.bpo-46131.ZBWQtO.rst

@@ -0,0 +1,2 @@
+Add a fast path for ``PyFloat_Check`` via a ``Py_TPFLAGS_FLOAT_SUBCLASS``
+flag.

Objects/floatobject.c

@@ -1959,6 +1959,7 @@ PyTypeObject PyFloat_Type = {
     0,                                          /* tp_setattro */
     0,                                          /* tp_as_buffer */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+        Py_TPFLAGS_FLOAT_SUBCLASS |
         _Py_TPFLAGS_MATCH_SELF,               /* tp_flags */
     float_new__doc__,                           /* tp_doc */
     0,                                          /* tp_traverse */

Objects/typeobject.c

@@ -5783,6 +5783,9 @@ inherit_special(PyTypeObject *type, PyTypeObject *base)
     else if (PyType_IsSubtype(base, &PyDict_Type)) {
         type->tp_flags |= Py_TPFLAGS_DICT_SUBCLASS;
     }
+    else if (PyType_IsSubtype(base, &PyFloat_Type)) {
+        type->tp_flags |= Py_TPFLAGS_FLOAT_SUBCLASS;
+    }
     if (PyType_HasFeature(base, _Py_TPFLAGS_MATCH_SELF)) {
         type->tp_flags |= _Py_TPFLAGS_MATCH_SELF;
     }

Tools/gdb/libpython.py

@@ -85,6 +85,7 @@ def _sizeof_void_p():
 
 Py_TPFLAGS_MANAGED_DICT      = (1 << 4)
 Py_TPFLAGS_HEAPTYPE          = (1 << 9)
+Py_TPFLAGS_FLOAT_SUBCLASS    = (1 << 23)
 Py_TPFLAGS_LONG_SUBCLASS     = (1 << 24)
 Py_TPFLAGS_LIST_SUBCLASS     = (1 << 25)
 Py_TPFLAGS_TUPLE_SUBCLASS    = (1 << 26)
@@ -379,6 +380,8 @@ def subclass_from_type(cls, t):
         if tp_flags & Py_TPFLAGS_HEAPTYPE:
             return HeapTypeObjectPtr
 
+        if tp_flags & Py_TPFLAGS_FLOAT_SUBCLASS:
+            return PyFloatObjectPtr
         if tp_flags & Py_TPFLAGS_LONG_SUBCLASS:
             return PyLongObjectPtr
         if tp_flags & Py_TPFLAGS_LIST_SUBCLASS:
@@ -910,6 +913,16 @@ class PyNoneStructPtr(PyObjectPtr):
     def proxyval(self, visited):
         return None
 
+class PyFloatObjectPtr(PyObjectPtr):
+    _typename = 'PyFloatObject'
+
+    def proxyval(self, visited):
+        return self.field('ob_fval')
+
+    def write_repr(self, out, visited):
+        proxy = self.proxyval(visited)
+        out.write("%s" % proxy)
+
 class PyFrameObjectPtr(PyObjectPtr):
     _typename = 'PyFrameObject'