bpo-37207: Use PEP 590 vectorcall to speed up tuple() (GH-18936)

Master:

./python.exe -m pyperf timeit "tuple((1, 2, 3, 4, 5))"
Mean +- std dev: 361 ns +- 15 ns

PEP-590:

./python.exe -m pyperf timeit "tuple((1, 2, 3, 4, 5))"
Mean +- std dev: 203 ns +- 13 ns

Author: corona10

Misc/NEWS.d/next/Core and Builtins/2020-03-12-02-41-12.bpo-37207.ye7OM3.rst

@@ -0,0 +1,2 @@
+Speed up calls to ``tuple()`` by using the :pep:`590` ``vectorcall`` calling
+convention. Patch by Dong-hee Na.

Objects/tupleobject.c

@@ -705,6 +705,26 @@ tuple_new_impl(PyTypeObject *type, PyObject *iterable)
         return PySequence_Tuple(iterable);
 }
 
+static PyObject *
+tuple_vectorcall(PyObject *type, PyObject * const*args,
+                 size_t nargsf, PyObject *kwnames)
+{
+    if (kwnames && PyTuple_GET_SIZE(kwnames) != 0) {
+        PyErr_Format(PyExc_TypeError, "tuple() takes no keyword arguments");
+        return NULL;
+    }
+    Py_ssize_t nargs = PyVectorcall_NARGS(nargsf);
+    if (nargs > 1) {
+        PyErr_Format(PyExc_TypeError, "tuple() expected at most 1 argument, got %zd", nargs);
+        return NULL;
+    }
+
+    if (nargs) {
+        return tuple_new_impl((PyTypeObject *)type, args[0]);
+    }
+    return PyTuple_New(0);
+}
+
 static PyObject *
 tuple_subtype_new(PyTypeObject *type, PyObject *iterable)
 {
@@ -863,6 +883,7 @@ PyTypeObject PyTuple_Type = {
     0,                                          /* tp_alloc */
     tuple_new,                                  /* tp_new */
     PyObject_GC_Del,                            /* tp_free */
+    .tp_vectorcall = tuple_vectorcall,
 };
 
 /* The following function breaks the notion that tuples are immutable: