Argument Clinic generates `{NULL, NULL}` initializer for Py_buffer variables. Such initializer zeroes all Py_buffer members, but as I understand only `obj` and `buf` members are really had to be initialized. Avoiding unneeded initialization provides tiny speed-up:

$ python -m perf timeit -s "replace = b''.replace" "replace(b'', b'')" --compare-to=../cpython-master/venv/bin/python --duplicate=1000
/home/sergey/tmp/cpython-master/venv/bin/python: ..................... 43.0 ns +- 0.5 ns
/home/sergey/tmp/cpython-dev/venv/bin/python: ..................... 41.8 ns +- 0.4 ns

Mean +- std dev: [/home/sergey/tmp/cpython-master/venv/bin/python] 43.0 ns +- 0.5 ns -> [/home/sergey/tmp/cpython-dev/venv/bin/python] 41.8 ns +- 0.4 ns: 1.03x faster (-3%)