python · Fidget-Spinner · Apr 25, 2025 · Apr 25, 2025 · Apr 25, 2025 · Apr 25, 2025
diff --git a/Lib/test/test_capi/test_opt.py b/Lib/test/test_capi/test_opt.py
@@ -1911,6 +1911,18 @@ def testfunc(n):
         self.assertNotIn("_COMPARE_OP_INT", uops)
         self.assertNotIn("_GUARD_IS_TRUE_POP", uops)
 
+    def test_call_len(self):
+        def testfunc(n):
+            a = [1, 2, 3, 4]
+            for _ in range(n):
+                _ = len(a) - 1
+
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
-            a = [1, 2, 3, 4]
-            for _ in range(n):
-                _ = len(a) - 1
-
-        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+            x = 0
+            a = [1, 2, 3, 4]
+            for _ in range(n):
+                _ = len(a) - 1
+                if _ == 3:
+                    x += 1
+
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
-            a = [1, 2, 3, 4]
-            for _ in range(n):
-                _ = len(a) - 1
-
-        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+            x = 0
+            a = [1, 2, 3, 4]
+            for _ in range(n):
+                _ = len(a) - 1
+                if _ == 3:
+                    x += 1
+
+        _, ex = self._run_with_optimizer(testfunc, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD)
+        uops = get_opnames(ex)
+        self.assertNotIn("_GUARD_NOS_INT", uops)
+        self.assertNotIn("_GUARD_TOS_INT", uops)
+        self.assertIn("_CALL_LEN", uops)
+
 
 def global_identity(x):
     return x

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-04-25-14-56-45.gh-issue-131798.NpcKub.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-04-25-14-56-45.gh-issue-131798.NpcKub.rst
@@ -0,0 +1 @@
+Allow the JIT to remove int guards after ``_CALL_LEN`` by setting the return type to int. Patch by Diego Russo
@@ -1055,6 +1055,10 @@ dummy_func(void) {
         sym_set_const(callable, (PyObject *)&PyUnicode_Type);
     }
 
+    op(_CALL_LEN, (callable[1], self_or_null[1], args[oparg] -- res)) {
+        res = sym_new_type(ctx, &PyLong_Type);
+    }
+
 // END BYTECODES //
 
 }
diff --git a/Python/optimizer_cases.c.h b/Python/optimizer_cases.c.h
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Allow the JIT to remove int guards after ``_CALL_LEN`` by setting the return type to int. Patch by Diego Russo