[3.13] pythonGH-123545: Remove duplicate Py_DECREF when handling _PyOptimizer_Optimize errors (pythonGH-123546)

(cherry picked from commit 1fbc118)

Co-authored-by: Savannah Ostrowski <[email protected]>

Author: savannahostrowski

Misc/NEWS.d/next/Core_and_Builtins/2024-09-01-00-02-05.gh-issue-123545.8nQNbL.rst

@@ -0,0 +1 @@
+Fix a double decref in rare cases on experimental JIT builds.

Python/bytecodes.c

@@ -4224,8 +4224,54 @@ dummy_func(
             #endif
         }
 
-        tier2 op(_EXIT_TRACE, (--)) {
-            EXIT_TO_TRACE();
+        tier2 op(_EXIT_TRACE, (exit_p/4 --)) {
+            _PyExitData *exit = (_PyExitData *)exit_p;
+            PyCodeObject *code = _PyFrame_GetCode(frame);
+            _Py_CODEUNIT *target = _PyCode_CODE(code) + exit->target;
+        #if defined(Py_DEBUG) && !defined(_Py_JIT)
+            OPT_HIST(trace_uop_execution_counter, trace_run_length_hist);
+            if (lltrace >= 2) {
+                printf("SIDE EXIT: [UOp ");
+                _PyUOpPrint(&next_uop[-1]);
+                printf(", exit %u, temp %d, target %d -> %s]\n",
+                    exit - current_executor->exits, exit->temperature.as_counter,
+                    (int)(target - _PyCode_CODE(code)),
+                    _PyOpcode_OpName[target->op.code]);
+            }
+        #endif
+            if (exit->executor && !exit->executor->vm_data.valid) {
+                exit->temperature = initial_temperature_backoff_counter();
+                Py_CLEAR(exit->executor);
+            }
+            if (exit->executor == NULL) {
+                _Py_BackoffCounter temperature = exit->temperature;
+                if (!backoff_counter_triggers(temperature)) {
+                    exit->temperature = advance_backoff_counter(temperature);
+                    tstate->previous_executor = (PyObject *)current_executor;
+                    GOTO_TIER_ONE(target);
+                }
+                _PyExecutorObject *executor;
+                if (target->op.code == ENTER_EXECUTOR) {
+                    executor = code->co_executors->executors[target->op.arg];
+                    Py_INCREF(executor);
+                }
+                else {
+                    int chain_depth = current_executor->vm_data.chain_depth + 1;
+                    int optimized = _PyOptimizer_Optimize(frame, target, stack_pointer, &executor, chain_depth);
+                    if (optimized <= 0) {
+                        exit->temperature = restart_backoff_counter(temperature);
+                        if (optimized < 0) {
+                            GOTO_UNWIND();
+                        }
+                        tstate->previous_executor = (PyObject *)current_executor;
+                        GOTO_TIER_ONE(target);
+                    }
+                }
+                exit->executor = executor;
+            }
+            Py_INCREF(exit->executor);
+            tstate->previous_executor = (PyObject *)current_executor;
+            GOTO_TIER_TWO(exit->executor);
         }
 
         tier2 op(_CHECK_VALIDITY, (--)) {
@@ -4322,8 +4368,6 @@ dummy_func(
                 if (optimized <= 0) {
                     exit->temperature = restart_backoff_counter(exit->temperature);
                     if (optimized < 0) {
-                        Py_DECREF(current_executor);
-                        tstate->previous_executor = Py_None;
                         GOTO_UNWIND();
                     }
                     GOTO_TIER_ONE(target);