From b3da6989524001d707ebb386bfab998452aa57bb Mon Sep 17 00:00:00 2001 From: Pieter Eendebak Date: Tue, 27 Dec 2022 11:55:54 +0100 Subject: gh-94603: micro optimize list.pop (gh-94604) --- .../2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst | 1 + Objects/listobject.c | 32 ++++++++++++++-------- 2 files changed, 21 insertions(+), 12 deletions(-) create mode 100644 Misc/NEWS.d/next/Core and Builtins/2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst diff --git a/Misc/NEWS.d/next/Core and Builtins/2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst b/Misc/NEWS.d/next/Core and Builtins/2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst new file mode 100644 index 0000000..de4fe4d --- /dev/null +++ b/Misc/NEWS.d/next/Core and Builtins/2022-07-06-18-44-00.gh-issue-94603.Q_03xV.rst @@ -0,0 +1 @@ +Improve performance of ``list.pop`` for small lists. diff --git a/Objects/listobject.c b/Objects/listobject.c index 1d32915..b093f88 100644 --- a/Objects/listobject.c +++ b/Objects/listobject.c @@ -1022,21 +1022,29 @@ list_pop_impl(PyListObject *self, Py_ssize_t index) PyErr_SetString(PyExc_IndexError, "pop index out of range"); return NULL; } - v = self->ob_item[index]; - if (index == Py_SIZE(self) - 1) { - status = list_resize(self, Py_SIZE(self) - 1); - if (status >= 0) - return v; /* and v now owns the reference the list had */ - else - return NULL; + + PyObject **items = self->ob_item; + v = items[index]; + const Py_ssize_t size_after_pop = Py_SIZE(self) - 1; + if (size_after_pop == 0) { + Py_INCREF(v); + status = _list_clear(self); } - Py_INCREF(v); - status = list_ass_slice(self, index, index+1, (PyObject *)NULL); - if (status < 0) { - Py_DECREF(v); + else { + if ((size_after_pop - index) > 0) { + memmove(&items[index], &items[index+1], (size_after_pop - index) * sizeof(PyObject *)); + } + status = list_resize(self, size_after_pop); + } + if (status >= 0) { + return v; // and v now owns the reference the list had + } + else { + // list resize failed, need to restore + memmove(&items[index+1], &items[index], (size_after_pop - index)* sizeof(PyObject *)); + items[index] = v; return NULL; } - return v; } /* Reverse a slice of a list in place, from lo up to (exclusive) hi. */ -- cgit v0.12