Replace PyObject_CallFunction() with fastcall

Replace
    PyObject_CallFunction(func, "O", arg)
and
    PyObject_CallFunction(func, "O", arg, NULL)
with
    _PyObject_CallArg1(func, arg)

Replace
    PyObject_CallFunction(func, NULL)
with
    _PyObject_CallNoArg(func)

_PyObject_CallNoArg() and _PyObject_CallArg1() are simpler and don't allocate
memory on the C stack.

Python/_warnings.c

@@ -476,7 +476,7 @@ warn_explicit(PyObject *category, PyObject *message,
     }
     else {
         text = message;
-        message = PyObject_CallFunction(category, "O", message);
+        message = _PyObject_CallArg1(category, message);
         if (message == NULL)
             goto cleanup;
     }

Python/codecs.c

@@ -284,7 +284,7 @@ PyObject *codec_makeincrementalcodec(PyObject *codec_info,
     if (errors)
         ret = PyObject_CallFunction(inccodec, "s", errors);
     else
-        ret = PyObject_CallFunction(inccodec, NULL);
+        ret = _PyObject_CallNoArg(inccodec);
     Py_DECREF(inccodec);
     return ret;
 }
@@ -322,7 +322,7 @@ PyObject *codec_getstreamcodec(const char *encoding,
     if (errors != NULL)
         streamcodec = PyObject_CallFunction(codeccls, "Os", stream, errors);
     else
-        streamcodec = PyObject_CallFunction(codeccls, "O", stream);
+        streamcodec = _PyObject_CallArg1(codeccls, stream);
     Py_DECREF(codecs);
     return streamcodec;
 }

Python/marshal.c

@@ -1274,7 +1274,7 @@ r_object(RFILE *p)
 
         if (n == 0 && type == TYPE_FROZENSET) {
             /* call frozenset() to get the empty frozenset singleton */
-            v = PyObject_CallFunction((PyObject*)&PyFrozenSet_Type, NULL);
+            v = _PyObject_CallNoArg((PyObject*)&PyFrozenSet_Type);
             if (v == NULL)
                 break;
             R_REF(v);