[3.13] gh-118692: Avoid creating unnecessary StopIteration instances for monitoring (GH-119216) (#119497)

* gh-118692: Avoid creating unnecessary StopIteration instances for monitoring (GH-119216)
(cherry picked from commit 6e9863d7a3516cc76d6ce13923b15620499f3855)

---------

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>

4 files changed, 21 insertions, 18 deletions

diff --git a/Python/bytecodes.c b/Python/bytecodes.c
index 55eda97..434eb80 100644
--- a/Python/bytecodes.c
+++ b/Python/bytecodes.c
@@ -292,11 +292,9 @@ dummy_func(
             /* Need to create a fake StopIteration error here,
              * to conform to PEP 380 */
             if (PyGen_Check(receiver)) {
-                PyErr_SetObject(PyExc_StopIteration, value);
-                if (monitor_stop_iteration(tstate, frame, this_instr)) {
+                if (monitor_stop_iteration(tstate, frame, this_instr, value)) {
                     ERROR_NO_POP();
                 }
-                PyErr_SetRaisedException(NULL);
             }
             DECREF_INPUTS();
         }
@@ -307,11 +305,9 @@ dummy_func(
 
         tier1 inst(INSTRUMENTED_END_SEND, (receiver, value -- value)) {
             if (PyGen_Check(receiver) || PyCoro_CheckExact(receiver)) {
-                PyErr_SetObject(PyExc_StopIteration, value);
-                if (monitor_stop_iteration(tstate, frame, this_instr)) {
+                if (monitor_stop_iteration(tstate, frame, this_instr, value)) {
                     ERROR_NO_POP();
                 }
-                PyErr_SetRaisedException(NULL);
             }
             Py_DECREF(receiver);
         }
diff --git a/Python/ceval.c b/Python/ceval.c
index 128e041..324d062 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -231,7 +231,8 @@ static void monitor_reraise(PyThreadState *tstate,
                  _Py_CODEUNIT *instr);
 static int monitor_stop_iteration(PyThreadState *tstate,
                  _PyInterpreterFrame *frame,
-                 _Py_CODEUNIT *instr);
+                 _Py_CODEUNIT *instr,
+                 PyObject *value);
 static void monitor_unwind(PyThreadState *tstate,
                  _PyInterpreterFrame *frame,
                  _Py_CODEUNIT *instr);
@@ -2215,12 +2216,19 @@ monitor_reraise(PyThreadState *tstate, _PyInterpreterFrame *frame,
 
 static int
 monitor_stop_iteration(PyThreadState *tstate, _PyInterpreterFrame *frame,
-                       _Py_CODEUNIT *instr)
+                       _Py_CODEUNIT *instr, PyObject *value)
 {
     if (no_tools_for_local_event(tstate, frame, PY_MONITORING_EVENT_STOP_ITERATION)) {
         return 0;
     }
-    return do_monitor_exc(tstate, frame, instr, PY_MONITORING_EVENT_STOP_ITERATION);
+    assert(!PyErr_Occurred());
+    PyErr_SetObject(PyExc_StopIteration, value);
+    int res = do_monitor_exc(tstate, frame, instr, PY_MONITORING_EVENT_STOP_ITERATION);
+    if (res < 0) {
+        return res;
+    }
+    PyErr_SetRaisedException(NULL);
+    return 0;
 }
 
 static void
diff --git a/Python/generated_cases.c.h b/Python/generated_cases.c.h
index 8b81122..96161c5 100644
--- a/Python/generated_cases.c.h
+++ b/Python/generated_cases.c.h
@@ -3260,11 +3260,9 @@
             /* Need to create a fake StopIteration error here,
              * to conform to PEP 380 */
             if (PyGen_Check(receiver)) {
-                PyErr_SetObject(PyExc_StopIteration, value);
-                if (monitor_stop_iteration(tstate, frame, this_instr)) {
+                if (monitor_stop_iteration(tstate, frame, this_instr, value)) {
                     goto error;
                 }
-                PyErr_SetRaisedException(NULL);
             }
             Py_DECREF(value);
             stack_pointer += -1;
@@ -3281,11 +3279,9 @@
             value = stack_pointer[-1];
             receiver = stack_pointer[-2];
             if (PyGen_Check(receiver) || PyCoro_CheckExact(receiver)) {
-                PyErr_SetObject(PyExc_StopIteration, value);
-                if (monitor_stop_iteration(tstate, frame, this_instr)) {
+                if (monitor_stop_iteration(tstate, frame, this_instr, value)) {
                     goto error;
                 }
-                PyErr_SetRaisedException(NULL);
             }
             Py_DECREF(receiver);
             stack_pointer[-2] = value;
diff --git a/Python/instrumentation.c b/Python/instrumentation.c
index 77d3489..9095fb9 100644
--- a/Python/instrumentation.c
+++ b/Python/instrumentation.c
@@ -2622,7 +2622,7 @@ exception_event_teardown(int err, PyObject *exc) {
     }
     else {
         assert(PyErr_Occurred());
-        Py_DECREF(exc);
+        Py_XDECREF(exc);
     }
     return err;
 }
@@ -2712,15 +2712,18 @@ _PyMonitoring_FirePyUnwindEvent(PyMonitoringState *state, PyObject *codelike, in
 }
 
 int
-_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset)
+_PyMonitoring_FireStopIterationEvent(PyMonitoringState *state, PyObject *codelike, int32_t offset, PyObject *value)
 {
     int event = PY_MONITORING_EVENT_STOP_ITERATION;
     assert(state->active);
+    assert(!PyErr_Occurred());
+    PyErr_SetObject(PyExc_StopIteration, value);
     PyObject *exc;
     if (exception_event_setup(&exc, event) < 0) {
         return -1;
     }
     PyObject *args[4] = { NULL, NULL, NULL, exc };
     int err = capi_call_instrumentation(state, codelike, offset, args, 3, event);
-    return exception_event_teardown(err, exc);
+    Py_DECREF(exc);
+    return exception_event_teardown(err, NULL);
 }