gh-145192: improve performance of PySequence_GetSlice (#145193)

Author: eendebakpt

Include/internal/pycore_sliceobject.h

@@ -12,7 +12,7 @@ extern "C" {
 /* runtime lifecycle */
 
 PyAPI_FUNC(PyObject *)
-_PyBuildSlice_ConsumeRefs(PyObject *start, PyObject *stop);
+_PyBuildSlice_ConsumeRefs(PyObject *start, PyObject *stop, PyObject *step);
 
 #ifdef __cplusplus
 }

Modules/_testinternalcapi/test_cases.c.h

@@ -117,8 +117,8 @@ PyObject _Py_EllipsisObject = _PyObject_HEAD_INIT(&PyEllipsis_Type);
    index is present.
 */
 
-static PySliceObject *
-_PyBuildSlice_Consume2(PyObject *start, PyObject *stop, PyObject *step)
+PyObject *
+_PyBuildSlice_ConsumeRefs(PyObject *start, PyObject *stop, PyObject *step)
 {
     assert(start != NULL && stop != NULL && step != NULL);
     PySliceObject *obj = _Py_FREELIST_POP(PySliceObject, slices);
@@ -131,13 +131,14 @@ _PyBuildSlice_Consume2(PyObject *start, PyObject *stop, PyObject *step)
 
     obj->start = start;
     obj->stop = stop;
-    obj->step = Py_NewRef(step);
+    obj->step = step;
 
     _PyObject_GC_TRACK(obj);
-    return obj;
+    return (PyObject *)obj;
 error:
     Py_DECREF(start);
     Py_DECREF(stop);
+    Py_DECREF(step);
     return NULL;
 }
 
@@ -153,15 +154,8 @@ PySlice_New(PyObject *start, PyObject *stop, PyObject *step)
     if (stop == NULL) {
         stop = Py_None;
     }
-    return (PyObject *)_PyBuildSlice_Consume2(Py_NewRef(start),
-                                              Py_NewRef(stop), step);
-}
-
-PyObject *
-_PyBuildSlice_ConsumeRefs(PyObject *start, PyObject *stop)
-{
-    assert(start != NULL && stop != NULL);
-    return (PyObject *)_PyBuildSlice_Consume2(start, stop, Py_None);
+    return _PyBuildSlice_ConsumeRefs(Py_NewRef(start),
+                                              Py_NewRef(stop), Py_NewRef(step));
 }
 
 PyObject *
@@ -177,9 +171,7 @@ _PySlice_FromIndices(Py_ssize_t istart, Py_ssize_t istop)
         return NULL;
     }
 
-    slice = PySlice_New(start, end, NULL);
-    Py_DECREF(start);
-    Py_DECREF(end);
+    slice = _PyBuildSlice_ConsumeRefs(start, end, Py_None);
     return slice;
 }
 

Objects/sliceobject.c

@@ -1116,7 +1116,8 @@ dummy_func(
 
         op(_STORE_SLICE, (v, container, start, stop -- )) {
             PyObject *slice = _PyBuildSlice_ConsumeRefs(PyStackRef_AsPyObjectSteal(start),
-                                                        PyStackRef_AsPyObjectSteal(stop));
+                                                        PyStackRef_AsPyObjectSteal(stop),
+                                                        Py_None);
             int err;
             if (slice == NULL) {
                 err = 1;