gh-91625: Don't ignore extended args of adaptive opcodes (GH-91626)

Lib/test/test_unpack.py

@@ -151,5 +151,21 @@ def load_tests(loader, tests, pattern):
     return tests
 
 
+class TestCornerCases(unittest.TestCase):
+    def test_extended_oparg_not_ignored(self):
+        # https://github.com/python/cpython/issues/91625
+        target = "(" + "y,"*400 + ")"
+        code = f"""def unpack_400(x):
+            {target} = x
+            return y
+        """
+        ns = {}
+        exec(code, ns)
+        unpack_400 = ns["unpack_400"]
+        # Warm up the the function for quickening (PEP 659)
+        for _ in range(30):
+            y = unpack_400(range(400))
+            self.assertEqual(y, 399)
+
 if __name__ == "__main__":
     unittest.main()