[Reland] Python tracer. (#68325)
Summary:
There were two issues with the original PR:
1) My assumption that bound C functions could be trusted to stay alive was not valid. I'm still not entirely sure what was dying, but I've just added a cache so that the first time I see a function I collect the repr just like I was already doing with Python functions.
2) `std::regex` is known to be badly broken and prone to segfaults. Because I'm just doing a very simple prefix prune it's fine to do it manually; see `trimPrefix`. Long term we should move all of PyTorch to `re2` as the internal lint suggests, but CMake is hard and I couldn't get it to work.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/68325
Reviewed By: chaekit
Differential Revision: D32432596
Pulled By: robieta
fbshipit-source-id: 06fb4bcdc6933a3e76f6021ca69dc77a467e4b2e
