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Speed up zero-argument class patterns in match statements
A class pattern with no sub-patterns (`case C():`) is just an isinstance check, but it compiled to LOAD_COMMON_CONSTANT (empty names tuple) + MATCH_CLASS + COPY + POP_JUMP_IF_NONE + UNPACK_SEQUENCE 0, building and unpacking an empty attributes tuple every time. Compile it instead to a CALL_INTRINSIC_2 invoking a new INTRINSIC_MATCH_CLASS_ISINSTANCE, which performs the same PyType_Check and PyObject_IsInstance as _PyEval_MatchClass (including the identical TypeError when the pattern does not name a class) and pushes a bool. No new opcode is added. This is ~25% faster on a matching subject and ~14% faster on a non-matching subject for the zero-argument case, and is even faster than an equivalent isinstance() call since the intrinsic avoids a Python-level call frame. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
1 parent 1b0c05f commit c6cd07f

3 files changed

Lines changed: 32 additions & 1 deletion

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‎Include/internal/pycore_intrinsics.h‎

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -30,8 +30,9 @@
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#define INTRINSIC_TYPEVAR_WITH_CONSTRAINTS 3
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#define INTRINSIC_SET_FUNCTION_TYPE_PARAMS 4
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#define INTRINSIC_SET_TYPEPARAM_DEFAULT 5
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#define INTRINSIC_MATCH_CLASS_ISINSTANCE 6
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34-
#define MAX_INTRINSIC_2 5
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#define MAX_INTRINSIC_2 6
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typedef PyObject *(*intrinsic_func1)(PyThreadState* tstate, PyObject *value);
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typedef PyObject *(*intrinsic_func2)(PyThreadState* tstate, PyObject *value1, PyObject *value2);

‎Python/codegen.c‎

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -6180,6 +6180,17 @@ codegen_pattern_class(compiler *c, pattern_ty p, pattern_context *pc)
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PyObject *name = asdl_seq_GET(kwd_attrs, i);
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PyTuple_SET_ITEM(attr_names, i, Py_NewRef(name));
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}
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if (nargs + nattrs == 0) {
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// No sub-patterns (`case C():`). This is just an isinstance check.
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// Emit it as a CALL_INTRINSIC_2 instead of MATCH_CLASS so we avoid
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// loading the empty names tuple, building the (empty) attrs tuple and
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// unpacking it. The class is already on top of the subject. The
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// intrinsic consumes both and pushes a bool.
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Py_DECREF(attr_names);
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ADDOP_I(c, LOC(p), CALL_INTRINSIC_2, INTRINSIC_MATCH_CLASS_ISINSTANCE);
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RETURN_IF_ERROR(jump_to_fail_pop(c, LOC(p), pc, POP_JUMP_IF_FALSE));
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return SUCCESS;
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}
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ADDOP_LOAD_CONST_NEW(c, LOC(p), attr_names);
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ADDOP_I(c, LOC(p), MATCH_CLASS, nargs);
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ADDOP_I(c, LOC(p), COPY, 1);

‎Python/intrinsics.c‎

Lines changed: 19 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -254,6 +254,24 @@ prep_reraise_star(PyThreadState* unused, PyObject *orig, PyObject *excs)
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return _PyExc_PrepReraiseStar(orig, excs);
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}
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static PyObject *
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match_class_isinstance(PyThreadState* tstate, PyObject *subject, PyObject *type)
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{
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// Fast path for a class pattern with no sub-patterns (`case C():`).
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// Equivalent to the isinstance check performed by _PyEval_MatchClass,
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// including the same TypeError when the pattern does not name a class.
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if (!PyType_Check(type)) {
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_PyErr_SetString(tstate, PyExc_TypeError,
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"class pattern must refer to a class");
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return NULL;
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}
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int res = PyObject_IsInstance(subject, type);
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if (res < 0) {
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return NULL;
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}
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return PyBool_FromLong(res);
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}
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static PyObject *
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make_typevar_with_bound(PyThreadState* Py_UNUSED(ignored), PyObject *name,
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PyObject *evaluate_bound)
@@ -278,6 +296,7 @@ _PyIntrinsics_BinaryFunctions[] = {
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INTRINSIC_FUNC_ENTRY(INTRINSIC_TYPEVAR_WITH_CONSTRAINTS, make_typevar_with_constraints)
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INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_FUNCTION_TYPE_PARAMS, _Py_set_function_type_params)
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INTRINSIC_FUNC_ENTRY(INTRINSIC_SET_TYPEPARAM_DEFAULT, _Py_set_typeparam_default)
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INTRINSIC_FUNC_ENTRY(INTRINSIC_MATCH_CLASS_ISINSTANCE, match_class_isinstance)
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};
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#undef INTRINSIC_FUNC_ENTRY

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