The benchmark from the https://bugs.python.org/issue37207#msg364428 was executed by below script.

import pyperf

runner = pyperf.Runner()
runner.timeit(name="frozenset create test",
              stmt="frozenset([1, 2, 3, 4, 5])")

@vstinner

Updated, During I work on helper function, I updated my git client and
during this process, it makes duplicated commits 27db91d d467294 .
I resolved all confliction and now it works okay. I also checked reference leak
through ./python.exe -m test test_set -R 3:3and there was no leak ;-)

And performance improvement is still valid.

Mean +- std dev: [master] 2.30 us +- 0.10 us -> [pr] 2.10 us +- 0.06 us: 1.10x faster (-9%)

Thanks @corona10: 1.09x faster (-9%) is nice to have (-200 ns). And IMHO the change makes the code more readable with new comments.