[Python-checkins] [3.8] bpo-37233: use _PY_FASTCALL_SMALL_STACK in method_vectorcall (GH-13974)

[Inada Naoki]

https://github.com/python/cpython/commit/c7570d402e3ee8717615ffa020eb9e2215a77660
commit: c7570d402e3ee8717615ffa020eb9e2215a77660
branch: 3.8
author: Inada Naoki <songofacandy at gmail.com>
committer: GitHub <noreply at github.com>
date: 2019-07-03T21:46:07+09:00
summary:

[3.8] bpo-37233: use _PY_FASTCALL_SMALL_STACK in method_vectorcall (GH-13974)

(cherry picked from commit 988e6aa322fb61651812fa5a61ec73316c71b041)

Co-authored-by: Jeroen Demeyer <J.Demeyer at UGent.be>

files:
M Objects/classobject.c

diff --git a/Objects/classobject.c b/Objects/classobject.c
index 2415ed14cb15..efdb18ef86da 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -64,10 +64,16 @@ method_vectorcall(PyObject *method, PyObject *const *args,
         Py_ssize_t nkwargs = (kwnames == NULL) ? 0 : PyTuple_GET_SIZE(kwnames);
         PyObject **newargs;
         Py_ssize_t totalargs = nargs + nkwargs;
-        newargs = PyMem_Malloc((totalargs+1) * sizeof(PyObject *));
-        if (newargs == NULL) {
-            PyErr_NoMemory();
-            return NULL;
+        PyObject *newargs_stack[_PY_FASTCALL_SMALL_STACK];
+        if (totalargs <= (Py_ssize_t)Py_ARRAY_LENGTH(newargs_stack) - 1) {
+            newargs = newargs_stack;
+        }
+        else {
+            newargs = PyMem_Malloc((totalargs+1) * sizeof(PyObject *));
+            if (newargs == NULL) {
+                PyErr_NoMemory();
+                return NULL;
+            }
         }
         /* use borrowed references */
         newargs[0] = self;
@@ -77,7 +83,9 @@ method_vectorcall(PyObject *method, PyObject *const *args,
             memcpy(newargs + 1, args, totalargs * sizeof(PyObject *));
         }
         result = _PyObject_Vectorcall(func, newargs, nargs+1, kwnames);
-        PyMem_Free(newargs);
+        if (newargs != newargs_stack) {
+            PyMem_Free(newargs);
+        }
     }
     return result;
 }