gh-138912: Add fast path for match class patterns without sub-patterns (#144820)

Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>

Author: cdce8p

Doc/library/dis.rst

@@ -1899,32 +1899,38 @@ iterations of the loop.
 
    The operand determines which intrinsic function is called:
 
-   +------------------------------------------+-----------------------------------+
-   | Operand                                  | Description                       |
-   +==========================================+===================================+
-   | ``INTRINSIC_2_INVALID``                  | Not valid                         |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_PREP_RERAISE_STAR``          | Calculates the                    |
-   |                                          | :exc:`ExceptionGroup` to raise    |
-   |                                          | from a ``try-except*``.           |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_TYPEVAR_WITH_BOUND``         | Creates a :class:`typing.TypeVar` |
-   |                                          | with a bound.                     |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_TYPEVAR_WITH_CONSTRAINTS``   | Creates a                         |
-   |                                          | :class:`typing.TypeVar` with      |
-   |                                          | constraints.                      |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_SET_FUNCTION_TYPE_PARAMS``   | Sets the ``__type_params__``      |
-   |                                          | attribute of a function.          |
-   +------------------------------------------+-----------------------------------+
-   | ``INTRINSIC_ADD_CONDITIONAL_ANNOTATION`` | Adds an annotation index to the   |
-   |                                          | ``__conditional_annotations__``   |
-   |                                          | set.                              |
-   +------------------------------------------+-----------------------------------+
+   +------------------------------------------+-----------------------------------------+
+   | Operand                                  | Description                             |
+   +==========================================+=========================================+
+   | ``INTRINSIC_2_INVALID``                  | Not valid                               |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_PREP_RERAISE_STAR``          | Calculates the                          |
+   |                                          | :exc:`ExceptionGroup` to raise          |
+   |                                          | from a ``try-except*``.                 |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_TYPEVAR_WITH_BOUND``         | Creates a :class:`typing.TypeVar`       |
+   |                                          | with a bound.                           |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_TYPEVAR_WITH_CONSTRAINTS``   | Creates a                               |
+   |                                          | :class:`typing.TypeVar` with            |
+   |                                          | constraints.                            |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_SET_FUNCTION_TYPE_PARAMS``   | Sets the ``__type_params__``            |
+   |                                          | attribute of a function.                |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_ADD_CONDITIONAL_ANNOTATION`` | Adds an annotation index to the         |
+   |                                          | ``__conditional_annotations__``         |
+   |                                          | set.                                    |
+   +------------------------------------------+-----------------------------------------+
+   | ``INTRINSIC_MATCH_CLASS_ISINSTANCE``     | Do :func:`isinstance` checks for        |
+   |                                          | :ref:`Class patterns <class-patterns>`. |
+   +------------------------------------------+-----------------------------------------+
 
    .. versionadded:: 3.12
 
+   .. versionchanged:: 3.16
+      Added ``INTRINSIC_MATCH_CLASS_ISINSTANCE``.
+
 
 .. opcode:: LOAD_SPECIAL
 

Include/internal/pycore_intrinsics.h

@@ -31,8 +31,9 @@
 #define INTRINSIC_SET_FUNCTION_TYPE_PARAMS       4
 #define INTRINSIC_SET_TYPEPARAM_DEFAULT          5
 #define INTRINSIC_ADD_CONDITIONAL_ANNOTATION     6
+#define INTRINSIC_MATCH_CLASS_ISINSTANCE         7
 
-#define MAX_INTRINSIC_2                          6
+#define MAX_INTRINSIC_2                          7
 
 typedef PyObject *(*intrinsic_func1)(PyThreadState* tstate, PyObject *value);
 typedef PyObject *(*intrinsic_func2)(PyThreadState* tstate, PyObject *value1, PyObject *value2);

Lib/test/test_capi/test_opt.py

@@ -5752,12 +5752,13 @@ def testfunc(n):
     def test_match_class(self):
         def testfunc(n):
             class A:
+                __match_args__ = ("val",)
                 val = 1
             x = A()
             ret = 0
             for _ in range(n):
                 match x:
-                    case A():
+                    case A(1):
                         ret += x.val
             return ret
 
@@ -5766,7 +5767,7 @@ class A:
         uops = get_opnames(ex)
 
         self.assertIn("_MATCH_CLASS", uops)
-        self.assertEqual(count_ops(ex, "_POP_TOP_NOP"), 4)
+        self.assertEqual(count_ops(ex, "_POP_TOP_NOP"), 5)
 
     def test_dict_update(self):
         def testfunc(n):

Misc/NEWS.d/next/Core_and_Builtins/2026-02-14-16-19-22.gh-issue-138912.TKMC9K.rst

@@ -0,0 +1,2 @@
+Add fast path for :keyword:`match` class patterns without any sub-patterns
+to improve performance by ~15%.

Python/codegen.c

@@ -6245,6 +6245,13 @@ codegen_pattern_class(compiler *c, pattern_ty p, pattern_context *pc)
     if (nattrs) {
         RETURN_IF_ERROR(validate_kwd_attrs(c, kwd_attrs, kwd_patterns));
     }
+    if (nargs + nattrs == 0) {
+        // Fast path if there are no sub-patterns
+        VISIT(c, expr, p->v.MatchClass.cls);
+        ADDOP_I(c, LOC(p), CALL_INTRINSIC_2, INTRINSIC_MATCH_CLASS_ISINSTANCE);
+        RETURN_IF_ERROR(jump_to_fail_pop(c, LOC(p), pc, POP_JUMP_IF_FALSE));
+        return SUCCESS;
+    }
     VISIT(c, expr, p->v.MatchClass.cls);
     PyObject *attr_names = PyTuple_New(nattrs);
     if (attr_names == NULL) {

Python/intrinsics.c

@@ -287,6 +287,25 @@ add_conditional_annotation(PyThreadState* tstate, PyObject *conditional_annotati
     Py_RETURN_NONE;
 }
 
+static PyObject *
+match_class_isinstance(PyThreadState* tstate, PyObject *subject, PyObject *type)
+{
+    /* Fast path for class patterns with no sub-patterns, e.g. `case C():`
+       Equivalent to the isinstance check performed by _PyEval_MatchClass,
+       including the same TypeError when the pattern does not refer to a
+       class. */
+    if (!PyType_Check(type)) {
+        _PyErr_SetString(tstate, PyExc_TypeError,
+                         "class pattern must refer to a class");
+        return NULL;
+    }
+    int res = PyObject_IsInstance(subject, type);
+    if (res < 0) {
+        return NULL;
+    }
+    return res ? Py_True : Py_False;
+}
+
 const intrinsic_func2_info
 _PyIntrinsics_BinaryFunctions[] = {
     INTRINSIC_FUNC_ENTRY(INTRINSIC_2_INVALID, no_intrinsic2)
@@ -296,6 +315,7 @@ _PyIntrinsics_BinaryFunctions[] = {
     INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_FUNCTION_TYPE_PARAMS, _Py_set_function_type_params)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_TYPEPARAM_DEFAULT, _Py_set_typeparam_default)
     INTRINSIC_FUNC_ENTRY(INTRINSIC_ADD_CONDITIONAL_ANNOTATION, add_conditional_annotation)
+    INTRINSIC_FUNC_ENTRY(INTRINSIC_MATCH_CLASS_ISINSTANCE, match_class_isinstance)
 };
 
 #undef INTRINSIC_FUNC_ENTRY