Add narrowing to constant unit test

Author: reidenong

Lib/test/test_capi/test_opt.py

@@ -1,17 +1,21 @@
+import _opcode
 import contextlib
+import gc
 import itertools
+import os
 import sys
 import textwrap
-import unittest
-import gc
-import os
 import types
+import unittest
 
-import _opcode
-
-from test.support import (script_helper, requires_specialization,
-                          import_helper, Py_GIL_DISABLED, requires_jit_enabled,
-                          reset_code)
+from test.support import (
+    Py_GIL_DISABLED,
+    import_helper,
+    requires_jit_enabled,
+    requires_specialization,
+    reset_code,
+    script_helper,
+)
 
 _testinternalcapi = import_helper.import_module("_testinternalcapi")
 
@@ -3574,6 +3578,25 @@ def return_false():
         # v + 1 should be constant folded
         self.assertNotIn("_BINARY_OP", uops)
 
+    def test_is_number_narrows_to_constant(self):
+        def f(n):
+            def return_1():
+                return 1
+
+            hits = 0
+            v = return_1()
+            for i in range(n):
+                if v is 1:
+                    hits += v + 1
+            return hits
+
+        res, ex = self._run_with_optimizer(f, TIER2_THRESHOLD)
+        self.assertEqual(res, TIER2_THRESHOLD * 2)
+        self.assertIsNotNone(ex)
+
+        # v + 1 should be constant folded
+        self.assertLessEqual(count_ops(ex, "_BINARY_OP_ADD_INT"), 1)
+
     def test_for_iter_gen_frame(self):
         def f(n):
             for i in range(n):