gh-131798: JIT: Narrow the return type of _GET_LEN to int

Lib/test/test_capi/test_opt.py

@@ -1925,6 +1925,50 @@ def testfunc(n):
  self.assertNotIn("_GUARD_NOS_INT", uops)
  self.assertNotIn("_GUARD_TOS_INT", uops)
 
+ def test_get_len_with_const_tuple(self):
+ def testfunc(n):
+ x = 0.0
+ for _ in range(n):
+ match (1, 2, 3, 4):
+ case [_, _, _, _]:
+ x += 1.0
+ return x
+ res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+ self.assertEqual(int(res), TIER2_THRESHOLD)
+ uops = get_opnames(ex)
+ self.assertNotIn("_GUARD_NOS_INT", uops)
+ self.assertNotIn("_GET_LEN", uops)
+ self.assertIn("_LOAD_CONST_INLINE_BORROW", uops)
+
+ def test_get_len_with_non_const_tuple(self):
+ def testfunc(n):
+ x = 0.0
+ for _ in range(n):
+ match object(), object():
+ case [_, _]:
+ x += 1.0
+ return x
+ res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+ self.assertEqual(int(res), TIER2_THRESHOLD)
+ uops = get_opnames(ex)
+ self.assertNotIn("_GUARD_NOS_INT", uops)
+ self.assertNotIn("_GET_LEN", uops)
+ self.assertIn("_LOAD_CONST_INLINE_BORROW", uops)
+
+ def test_get_len_with_non_tuple(self):
+ def testfunc(n):
+ x = 0.0
+ for _ in range(n):
+ match [1, 2, 3, 4]:
+ case [_, _, _, _]:
+ x += 1.0
+ return x
+ res, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+ self.assertEqual(int(res), TIER2_THRESHOLD)
+ uops = get_opnames(ex)
+ self.assertNotIn("_GUARD_NOS_INT", uops)
+ self.assertIn("_GET_LEN", uops)
+
  def test_binary_op_subscr_tuple_int(self):
  def testfunc(n):
  x = 0

Misc/NEWS.d/next/Core_and_Builtins/2025-05-03-22-31-53.gh-issue-131798.fQ0ato.rst

@@ -0,0 +1,2 @@
+Allow the JIT to remove int guards after ``_GET_LEN`` by setting the return
+type to int.

Python/optimizer_bytecodes.c

@@ -1116,6 +1116,25 @@ dummy_func(void) {
  res = sym_new_type(ctx, &PyLong_Type);
  }
 
+ op(_GET_LEN, (obj -- obj, len)) {
+ int tuple_length = sym_tuple_length(obj);
+ if (tuple_length == -1) {
+ len = sym_new_type(ctx, &PyLong_Type);
+ }
+ else {
+ assert(tuple_length >= 0);
+ PyObject *temp = PyLong_FromLong(tuple_length);
+ if (temp == NULL) {
+ goto error;
+ }
+ if (_Py_IsImmortal(temp)) {
+ REPLACE_OP(this_instr, _LOAD_CONST_INLINE_BORROW, 0, (uintptr_t)temp);
+ }
+ len = sym_new_const(ctx, temp);
+ Py_DECREF(temp);
+ }
+ }
+
  op(_GUARD_CALLABLE_LEN, (callable, unused, unused -- callable, unused, unused)) {
  PyObject *len = _PyInterpreterState_GET()->callable_cache.len;
  if (sym_get_const(ctx, callable) == len) {