gh-131586: Avoid refcount contention in context managers (gh-131851)

This avoid reference count contention in the free threading build
when calling special methods like `__enter__` and `__exit__`.

1 files changed, 20 insertions, 21 deletions

diff --git a/Python/executor_cases.c.h b/Python/executor_cases.c.h
index cd265c383bd..c65cc9efa5e 100644
--- a/Python/executor_cases.c.h
+++ b/Python/executor_cases.c.h
@@ -4407,43 +4407,42 @@
             break;
         }
 
+        case _INSERT_NULL: {
+            _PyStackRef self;
+            _PyStackRef *method_and_self;
+            self = stack_pointer[-1];
+            method_and_self = &stack_pointer[-1];
+            method_and_self[1] = self;
+            method_and_self[0] = PyStackRef_NULL;
+            stack_pointer += 1;
+            assert(WITHIN_STACK_BOUNDS());
+            break;
+        }
+
         case _LOAD_SPECIAL: {
-            _PyStackRef owner;
-            _PyStackRef attr;
-            _PyStackRef self_or_null;
+            _PyStackRef *method_and_self;
             oparg = CURRENT_OPARG();
-            owner = stack_pointer[-1];
-            assert(oparg <= SPECIAL_MAX);
-            PyObject *owner_o = PyStackRef_AsPyObjectSteal(owner);
+            method_and_self = &stack_pointer[-2];
             PyObject *name = _Py_SpecialMethods[oparg].name;
-            PyObject *self_or_null_o;
-            stack_pointer += -1;
-            assert(WITHIN_STACK_BOUNDS());
             _PyFrame_SetStackPointer(frame, stack_pointer);
-            PyObject *attr_o = _PyObject_LookupSpecialMethod(owner_o, name, &self_or_null_o);
+            int err = _PyObject_LookupSpecialMethod(name, method_and_self);
             stack_pointer = _PyFrame_GetStackPointer(frame);
-            if (attr_o == NULL) {
-                if (!_PyErr_Occurred(tstate)) {
+            if (err <= 0) {
+                if (err == 0) {
+                    PyObject *owner = PyStackRef_AsPyObjectBorrow(method_and_self[1]);
                     _PyFrame_SetStackPointer(frame, stack_pointer);
-                    const char *errfmt = _PyEval_SpecialMethodCanSuggest(owner_o, oparg)
+                    const char *errfmt = _PyEval_SpecialMethodCanSuggest(owner, oparg)
                     ? _Py_SpecialMethods[oparg].error_suggestion
                 : _Py_SpecialMethods[oparg].error;
                     stack_pointer = _PyFrame_GetStackPointer(frame);
                     assert(!_PyErr_Occurred(tstate));
                     assert(errfmt != NULL);
                     _PyFrame_SetStackPointer(frame, stack_pointer);
-                    _PyErr_Format(tstate, PyExc_TypeError, errfmt, owner_o);
+                    _PyErr_Format(tstate, PyExc_TypeError, errfmt, owner);
                     stack_pointer = _PyFrame_GetStackPointer(frame);
                 }
                 JUMP_TO_ERROR();
             }
-            attr = PyStackRef_FromPyObjectSteal(attr_o);
-            self_or_null = self_or_null_o == NULL ?
-            PyStackRef_NULL : PyStackRef_FromPyObjectSteal(self_or_null_o);
-            stack_pointer[0] = attr;
-            stack_pointer[1] = self_or_null;
-            stack_pointer += 2;
-            assert(WITHIN_STACK_BOUNDS());
             break;
         }