constexpr type ids (#26502)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/26502
Create type ids at compile time instead of incrementing a counter at runtime. This is done by computing a compile time crc64 on the type name. We couldn't do this before, because we still used GCC4 and that compiler didn't support the use of `__PRETTY_FUNCTION__` in a constexpr context. However, since GCC5 this is possible and we can use this trick.
This does not change the semantics of preallocated type ids. I actually think we don't need to preallocate anymore, but I split the removal of preallocation into a separate diff to be able to test it separately.
ghstack-source-id: 91896920
Test Plan: unit tests
Differential Revision: D17488861
fbshipit-source-id: ce7b059d7c8686b69cb091a4a8beaf4b96391343
