Manually generate guards for optimizer (#103121)
Manually generate guards for optimizer rather than use variable builder, which can be slow with lots of params.
This is the reason for ~10s compile slowdown
Redisable `_init_group`. This is important, because if for any reason a frame which calls `_init_group` is run in the python interpreter, we will trace it, which we don't want to do. We only want to call it when it is accessed via the fast path implemented with the optimizer variable during symbolic interpretation.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103121
Approved by: https://github.com/jansel
