gh-127274: Defer nested methods (#128012)

Methods (functions defined in class scope) are likely to be cleaned
up by the GC anyway.

Add a new code flag, `CO_METHOD`, that is set for functions defined
in a class scope. Use that when deciding to defer functions.

1 files changed, 5 insertions, 1 deletions

diff --git a/Objects/funcobject.c b/Objects/funcobject.c
index cca7f01..7b17a9b 100644
--- a/Objects/funcobject.c
+++ b/Objects/funcobject.c
@@ -210,10 +210,14 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
     op->func_typeparams = NULL;
     op->vectorcall = _PyFunction_Vectorcall;
     op->func_version = FUNC_VERSION_UNSET;
-    if ((code_obj->co_flags & CO_NESTED) == 0) {
+    if (((code_obj->co_flags & CO_NESTED) == 0) ||
+        (code_obj->co_flags & CO_METHOD)) {
         // Use deferred reference counting for top-level functions, but not
         // nested functions because they are more likely to capture variables,
         // which makes prompt deallocation more important.
+        //
+        // Nested methods (functions defined in class scope) are also deferred,
+        // since they will likely be cleaned up by GC anyway.
         _PyObject_SetDeferredRefcount((PyObject *)op);
     }
     _PyObject_GC_TRACK(op);