Revert "gh-149570: avoid tier-2 self-link in _COLD_EXIT"

This reverts commit da37760.

Author: NekoAsakura

Include/internal/pycore_ceval.h

@@ -351,10 +351,9 @@ _PyEval_SpecialMethodCanSuggest(PyObject *self, int oparg);
 #define _PY_EVAL_PLEASE_STOP_BIT (1U << 5)
 #define _PY_EVAL_EXPLICIT_MERGE_BIT (1U << 6)
 #define _PY_EVAL_JIT_INVALIDATE_COLD_BIT (1U << 7)
-#define _PY_EVAL_JIT_FORCE_TIER1_BIT (1U << 8)
 
 /* Reserve a few bits for future use */
-#define _PY_EVAL_EVENTS_BITS 9
+#define _PY_EVAL_EVENTS_BITS 8
 #define _PY_EVAL_EVENTS_MASK ((1 << _PY_EVAL_EVENTS_BITS)-1)
 
 static inline void

Lib/test/test_capi/test_opt.py

@@ -1,6 +1,5 @@
 import contextlib
 import itertools
-import subprocess
 import sys
 import textwrap
 import unittest
@@ -10,7 +9,7 @@
 
 import _opcode
 
-from test.support import (SHORT_TIMEOUT, script_helper, requires_specialization,
+from test.support import (script_helper, requires_specialization,
                           import_helper, Py_GIL_DISABLED, requires_jit_enabled,
                           reset_code)
 
@@ -5995,51 +5994,6 @@ def __init__(self, name):
              PYTHON_JIT_SIDE_EXIT_INITIAL_VALUE="1")
         self.assertEqual(result[0].rc, 0, result)
 
-    def test_side_exit_to_executor_makes_progress(self):
-        script = textwrap.dedent("""
-        classes = []
-
-        def make_iter():
-            class It:
-                def __init__(self):
-                    self.i = 0
-
-                def __iter__(self):
-                    return self
-
-                def __next__(self):
-                    self.i += 1
-                    if self.i > 1000:
-                        raise StopIteration
-                    return self.i
-
-            classes.append(It)
-            return It()
-
-        def f(n):
-            for outer in range(n):
-                for x in make_iter():
-                    pass
-
-        f(200)
-        """)
-        env = os.environ.copy()
-        env.update({
-            "PYTHON_JIT": "1",
-            "PYTHON_JIT_SIDE_EXIT_INITIAL_VALUE": "1",
-        })
-        try:
-            result = subprocess.run(
-                [sys.executable, "-X", "faulthandler", "-c", script],
-                stdout=subprocess.PIPE,
-                stderr=subprocess.PIPE,
-                env=env,
-                timeout=SHORT_TIMEOUT,
-            )
-        except subprocess.TimeoutExpired as exc:
-            self.fail(f"subprocess timed out: {exc}")
-        self.assertEqual(result.returncode, 0, result)
-
     def test_for_iter_gen_cleared_frame_does_not_crash(self):
         # See: https://github.com/python/cpython/issues/145197
         result = script_helper.run_python_until_end('-c', textwrap.dedent("""

Python/bytecodes.c

@@ -6297,16 +6297,6 @@ dummy_func(
             if (target->op.code == ENTER_EXECUTOR) {
                 PyCodeObject *code = _PyFrame_GetCode(frame);
                 executor = code->co_executors->executors[target->op.arg];
-                _PyExecutorObject *previous_executor = _PyExecutor_FromExit(exit);
-                if (!exit->is_control_flow) {
-                    int chain_depth = previous_executor->vm_data.chain_depth + 1;
-                    if (executor == previous_executor ||
-                        chain_depth % MAX_CHAIN_DEPTH == 0) {
-                        /* Avoid tier-2 self-link/wrap that bypasses the eval breaker. */
-                        _Py_set_eval_breaker_bit(tstate, _PY_EVAL_JIT_FORCE_TIER1_BIT);
-                        GOTO_TIER_ONE(target);
-                    }
-                }
                 Py_INCREF(executor);
                 assert(tstate->jit_exit == exit);
                 exit->executor = executor;

Python/ceval_gil.c

@@ -1403,10 +1403,6 @@ _Py_HandlePending(PyThreadState *tstate)
     }
 
 #ifdef _Py_TIER2
-    if ((breaker & _PY_EVAL_JIT_FORCE_TIER1_BIT) != 0) {
-        _Py_unset_eval_breaker_bit(tstate, _PY_EVAL_JIT_FORCE_TIER1_BIT);
-    }
-
     if ((breaker & _PY_EVAL_JIT_INVALIDATE_COLD_BIT) != 0) {
         _Py_unset_eval_breaker_bit(tstate, _PY_EVAL_JIT_INVALIDATE_COLD_BIT);
         _Py_Executors_InvalidateCold(tstate->interp);