Improve performance of inherited mapping assignment slot calls

Feature or enhancement

Proposal:

__setitem__ and __delitem__ share the mp_ass_subscript slot. If a Python subclass of a C mapping overrides only one of them, slot_mp_ass_subscript() is used for both operations.

For example, collections.Counter overrides __delitem__ but inherits dict.__setitem__. Assigning an item looks up the inherited wrapper_descriptor and calls it through the generic tp_call path. Since PyWrapperDescr_Type does not support vectorcall, _PyObject_MakeTpCall() and wrapperdescr_call() each create a temporary argument tuple before reaching dict's C slot.

Reproducer:

from collections import Counter
from time import perf_counter_ns

obj = Counter()

start = perf_counter_ns()
for index in range(20_000_000):
    obj[0] = index

print((perf_counter_ns() - start) / 1_000_000)

On macOS 15.7.1 arm64 with a release build of main (d856402e7176e5a03c5c578f0efc1be968be3257), using two warmups and nine alternating-order samples:

main:      1402.07 ms median (1376.93–1445.12 ms)
prototype:  859.97 ms median (846.24–902.74 ms)

The prototype calls the inherited C slot directly when lookup returns the expected unbound mapping slot wrapper, and otherwise keeps the existing call path. This reduced the benchmark time by 38.66%.

The relevant call-path files are unchanged at b062727097e997bcb900e11503d3248daac903da.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-156258

Bắt đầu bằng cách đọc các đường dẫn slot_mp_ass_subscript(), _PyObject_MakeTpCall() và wrapperdescr_call() được mô tả trong issue, sau đó kiểm tra PR được liên kết gh-156258. Công việc được xem là hoàn tất khi đường dẫn gán mapping được kế thừa tránh các tuple đối số tạm thời nhưng vẫn giữ fallback hiện có, và benchmark Counter được cung cấp cho thấy mức cải thiện đã báo cáo.