This PR makes a second pass over the constructor. The logic has been grouped into `_init_<...>` functions based on intent (e.g. `_init_prefetching_state()` or `_init_runtime_state()`). This makes the initialization code for composable FSDP much cleaner than having to re-write the same sequences of lower-level helper calls.
This PR also moves `_ExecOrderData` into its own file `_exec_order_utils.py`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87923
Approved by: https://github.com/mrshenli
The goal of this PR is to make one pass over the FSDP constructor and refactor each helper method call to not be `self.<...>`. Subsequent PRs will make further passes over the FSDP constructor.
This PR looks like a lot of lines of code change, but it is only reorganization. Methods are moved to `_init_utils.py` and `_common_utils.py`. This also marks the beginning of moving methods from `_utils.py` to `_common_utils.py` -- they will be coalesced eventually. I am only using `_common_utils.py` as a staging ground to include the methods that have been affected by the refactoring.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87921
Approved by: https://github.com/mrshenli
