gh-131586: Avoid refcount contention in some "special" calls (#131588)

In the free threaded build, the `_PyObject_LookupSpecial()` call can lead to
reference count contention on the returned function object becuase it
doesn't use stackrefs. Refactor some of the callers to use
`_PyObject_MaybeCallSpecialNoArgs`, which uses stackrefs internally.

This fixes the scaling bottleneck in the "lookup_special" microbenchmark
in `ftscalingbench.py`. However, the are still some uses of
`_PyObject_LookupSpecial()` that need to be addressed in future PRs.

1 files changed, 12 insertions, 15 deletions

diff --git a/Python/bltinmodule.c b/Python/bltinmodule.c
index f776120..7a12a86 100644
--- a/Python/bltinmodule.c
+++ b/Python/bltinmodule.c
@@ -2537,22 +2537,19 @@ static PyObject *
 builtin_round_impl(PyObject *module, PyObject *number, PyObject *ndigits)
 /*[clinic end generated code: output=ff0d9dd176c02ede input=275678471d7aca15]*/
 {
-    PyObject *round, *result;
-
-    round = _PyObject_LookupSpecial(number, &_Py_ID(__round__));
-    if (round == NULL) {
-        if (!PyErr_Occurred())
-            PyErr_Format(PyExc_TypeError,
-                         "type %.100s doesn't define __round__ method",
-                         Py_TYPE(number)->tp_name);
-        return NULL;
+    PyObject *result;
+    if (ndigits == Py_None) {
+        result = _PyObject_MaybeCallSpecialNoArgs(number, &_Py_ID(__round__));
+    }
+    else {
+        result = _PyObject_MaybeCallSpecialOneArg(number, &_Py_ID(__round__),
+                                                  ndigits);
+    }
+    if (result == NULL && !PyErr_Occurred()) {
+        PyErr_Format(PyExc_TypeError,
+                     "type %.100s doesn't define __round__ method",
+                     Py_TYPE(number)->tp_name);
     }
-
-    if (ndigits == Py_None)
-        result = _PyObject_CallNoArgs(round);
-    else
-        result = PyObject_CallOneArg(round, ndigits);
-    Py_DECREF(round);
     return result;
 }