Here are the benchmark results of freezing warnings.py as _frozen_warnings (very quick hack which doesn't use _frozen_warnings is attached). Basically -S slows down by about 3% and normal startup has no measurable impact. Not sure if that's worth it to simplify the warnings code or not.


INFO:root:Automatically selected timer: perf_counter
INFO:root:Skipping benchmark bzr_startup; not compatible with Python 3.6
INFO:root:Skipping benchmark hg_startup; not compatible with Python 3.6
Running normal_startup...
INFO:root:Running `../cpython/default/python.exe -c ` 1000 times
INFO:root:Running `../cpython/pristine/python.exe -c ` 1000 times
Running startup_nosite...
INFO:root:Running `../cpython/default/python.exe -S -c ` 2000 times
INFO:root:Running `../cpython/pristine/python.exe -S -c ` 2000 times

Report on Darwin Bretts-MacBook-Pro.local 14.5.0 Darwin Kernel Version 14.5.0: Wed Jul 29 02:26:53 PDT 2015; root:xnu-2782.40.9~1/RELEASE_X86_64 x86_64 i386
Total CPU cores: 4

### startup_nosite ###
Min: 0.311247 -> 0.317280: 1.02x slower
Avg: 0.316682 -> 0.325945: 1.03x slower
Significant (t=-17.89)
Stddev: 0.00326 -> 0.00403: 1.2360x larger

The following not significant results are hidden, use -v to show them:
normal_startup.