PERF: regression in PeriodIndex getitem / get_loc
#41670 seems to have caused slowdowns in several of the Period indexing benchmarks: see https://pandas.pydata.org/speed/pandas/#regressions?sort=1&dir=desc, scrolldown to "2021-05-28 17:58"

One example: https://pandas.pydata.org/speed/pandas/#period.Indexing.time_get_loc?python=3.8&Cython=0.29.21&commits=ddc28a42

_Originally posted by @jorisvandenbossche in https://github.com/pandas-dev/pandas/issues/41670#issuecomment-856835712_