[3.15] gh-154701: prevent executor self-links in JIT cold exits (GH-155323) (#155832)

(cherry picked from commit 716cbae)

Co-authored-by: Hai Zhu <haiizhu@outlook.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

* gh-154701: adapt JIT cold exit backport to 3.15

---------

Co-authored-by: Hai Zhu <haiizhu@outlook.com>
Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>

Author: 3 people

Include/internal/pycore_optimizer.h

@@ -206,7 +206,7 @@ typedef struct _PyExecutorObject {
 PyAPI_FUNC(_PyExecutorObject*) _Py_GetExecutor(PyCodeObject *code, int offset);
 
 int _Py_ExecutorInit(_PyExecutorObject *, const _PyBloomFilter *);
-void _Py_ExecutorDetach(_PyExecutorObject *);
+PyAPI_FUNC(void) _Py_ExecutorDetach(_PyExecutorObject *);
 PyAPI_FUNC(void) _Py_Executor_DependsOn(_PyExecutorObject *executor, void *obj);
 
 /* We use a bloomfilter with k = 6, m = 256

Include/internal/pycore_uop_metadata.h

@@ -5,13 +5,14 @@
 import unittest
 import gc
 import os
+import subprocess
 import types
 
 import _opcode
 
 from test.support import (script_helper, requires_specialization,
                           import_helper, Py_GIL_DISABLED, requires_jit_enabled,
-                          reset_code)
+                          reset_code, SHORT_TIMEOUT)
 
 _testinternalcapi = import_helper.import_module("_testinternalcapi")
 
@@ -6200,6 +6201,31 @@ def __exit__(self, e, v, t): ...
                 f1()
         """), PYTHON_JIT="1")
 
+    def test_for_iter_side_exit_does_not_self_link(self):
+        subprocess.run([sys.executable, "-c", textwrap.dedent("""
+            from _testinternalcapi import TIER2_THRESHOLD
+
+            def exhaust(iterator):
+                for _ in iterator:
+                    pass
+
+            values = range(TIER2_THRESHOLD)
+            # After the initial trace, MAX_CHAIN_DEPTH side exits cause the final
+            # executor to be installed at FOR_ITER.
+            warmup_iterators = (
+                iter(set(values)),
+                iter(dict.fromkeys(values)),
+                iter(values),
+                enumerate(values),
+                zip(values, values),
+            )
+            for iterator in warmup_iterators:
+                exhaust(iterator)
+
+            # A different iterator type must not link that executor to itself.
+            exhaust(map(bool, values))
+        """)], check=True, timeout=SHORT_TIMEOUT)
+
 def global_identity(x):
     return x
 

Lib/test/test_capi/test_opt.py

@@ -0,0 +1 @@
+Fix an infinite loop in JIT when a ``FOR_ITER`` side exit links an executor back to itself.

Misc/NEWS.d/next/Core_and_Builtins/2026-08-07-10-14-56.gh-issue-154701.zulh2S.rst

@@ -6308,6 +6308,10 @@ dummy_func(
             if (target->op.code == ENTER_EXECUTOR) {
                 PyCodeObject *code = _PyFrame_GetCode(frame);
                 executor = code->co_executors->executors[target->op.arg];
+                if (executor == _PyExecutor_FromExit(exit)) {
+                    _Py_ExecutorDetach(executor);
+                    GOTO_TIER_ONE(target);
+                }
                 Py_INCREF(executor);
                 assert(tstate->jit_exit == exit);
                 exit->executor = executor;