gh-131798: JIT: Assign type to sliced string/list/tuple

Lib/test/test_capi/test_opt.py

@@ -1655,13 +1655,11 @@ def testfunc(n):
  self.assertIn("_CONTAINS_OP_DICT", uops)
  self.assertNotIn("_TO_BOOL_BOOL", uops)
 
-
  def test_remove_guard_for_known_type_str(self):
  def f(n):
  for i in range(n):
  false = i == TIER2_THRESHOLD
  empty = "X"[:false]
- empty += "" # Make JIT realize this is a string.
  if empty:
  return 1
  return 0
@@ -2219,6 +2217,34 @@ def f(n):
  self.assertNotIn("_LOAD_ATTR_METHOD_NO_DICT", uops)
  self.assertNotIn("_LOAD_ATTR_METHOD_LAZY_DICT", uops)
 
+ def test_remove_guard_for_slice_list(self):
+ def f(n):
+ for i in range(n):
+ false = i == TIER2_THRESHOLD
+ sliced = [1, 2, 3][:false]
+ if sliced:
+ return 1
+ return 0
+
+ res, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+ self.assertEqual(res, 0)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ self.assertIn("_TO_BOOL_LIST", uops)
+ self.assertNotIn("_GUARD_TOS_LIST", uops)
+
+ def test_remove_guard_for_slice_tuple(self):
+ def f(n):
+ for i in range(n):
+ false = i == TIER2_THRESHOLD
+ a, b = (1, 2, 3)[: false + 2]
+
+ _, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+ self.assertIsNotNone(ex)
+ uops = get_opnames(ex)
+ self.assertIn("_UNPACK_SEQUENCE_TWO_TUPLE", uops)
+ self.assertNotIn("_GUARD_TOS_TUPLE", uops)
+
 
 def global_identity(x):
  return x

Misc/NEWS.d/next/Core_and_Builtins/2025-05-25-19-32-15.gh-issue-131798.f5h8aI.rst

@@ -0,0 +1 @@
+Make the JIT optimizer understand that slicing a string/list/tuple returns the same type.

Python/optimizer_bytecodes.c

@@ -1216,6 +1216,20 @@ dummy_func(void) {
  sym_set_const(callable, list_append);
  }
 
+ op(_BINARY_SLICE, (container, start, stop -- res)) {
+ // Slicing a string/list/tuple always returns the same type.
+ PyTypeObject *type = sym_get_type(container);
+ if (type == &PyUnicode_Type ||
+ type == &PyList_Type ||
+ type == &PyTuple_Type)
+ {
+ res = sym_new_type(ctx, type);
+ }
+ else {
+ res = sym_new_not_null(ctx);
+ }
+ }
+
 // END BYTECODES //
 
 }