gh-157875: Fix a reference leak when rewinding JIT traces

Lib/test/test_capi/test_opt.py

@@ -6016,6 +6016,28 @@ def f1():
         """), PYTHON_JIT="1")
         self.assertEqual(result[0].rc, 0, result)
 
+    def test_157875_rewound_trace_reference_leak(self):
+        # https://github.com/python/cpython/issues/157875
+        import weakref
+
+        def run():
+            class C:
+                def __iter__(self):
+                    return self
+
+                def __next__(self):
+                    raise StopIteration
+
+            obj = C()
+            for _ in range(TIER2_THRESHOLD):
+                for _ in obj:
+                    pass
+            return weakref.ref(C)
+
+        ref = run()
+        gc.collect()
+        self.assertIsNone(ref())
+
     def test_144068_daemon_thread_jit_cleanup(self):
         result = script_helper.run_python_until_end('-c', textwrap.dedent("""
         import threading

Misc/NEWS.d/next/Core_and_Builtins/2026-09-21-16-00-00.gh-issue-157875.7Qn4Jp.rst

@@ -0,0 +1,2 @@
+Fix a reference leak in the JIT when a trace is rewound after encountering
+unsupported bytecode.

Python/optimizer.c

@@ -789,6 +789,9 @@ _PyJit_translate_single_bytecode_to_trace(
         {
             _PyUOpInstruction *curr = uop_buffer_last(trace);
             while (curr->opcode != _SET_IP && uop_buffer_length(trace) > 2) {
+                if (_PyUop_Flags[curr->opcode] & HAS_RECORDS_VALUE_FLAG) {
+                    Py_XDECREF((PyObject *)(uintptr_t)curr->operand0);
+                }
                 trace->next--;
                 curr = uop_buffer_last(trace);
             }