Avoid creating temporary objects in BINARY_SLICE

Feature or enhancement

Proposal:

Currently BINARY_SLICE looks like this:

        op(_BINARY_SLICE, (container, start, stop -- res)) {
            PyObject *slice = _PyBuildSlice_ConsumeRefs(PyStackRef_AsPyObjectSteal(start),
                                                        PyStackRef_AsPyObjectSteal(stop));
            PyObject *res_o;
            if (slice == NULL) {
                res_o = NULL;
            }
            else {
                res_o = PyObject_GetItem(PyStackRef_AsPyObjectBorrow(container), slice);
                Py_DECREF(slice);
            }
            PyStackRef_CLOSE(container);
            ERROR_IF(res_o == NULL);
            res = PyStackRef_FromPyObjectSteal(res_o);
        }

Note that we build a slice just for getitem, only to throw it away immediately after.

We can scalar replace the slice in BINARY_SLICE after recording the types. If we record the container type, we can call the slice dispatcher underneath directly without boxing the slice object. See for example BINARY_OP_SUBSCR_LIST_SLICE

We'd need to guard on the type recorded.

I propose to do this in the current optimizer pass rather than the partial evaluation pass, as this is just a simple optimization within a single op, while the PE pass can handle inter-instruction optimization.

Has this already been discussed elsewhere?

No response given

Links to previous discussion of this feature:

No response

Linked PRs

• gh-144590
• gh-156318

BINARY_SLICE エントリポイントから始め、現在のオプティマイザーパスにある BINARY_OP_SUBSCR_LIST_SLICE と比較します。また、示されている境界を理解するために部分評価パスも読んでください。記録されたコンテナ型がガードされ、スライシングのディスパッチが一時的なスライスオブジェクトの作成を回避し、動作が維持されていれば完了です。