Edit: I might be wrong on the following, so please ignore the rest.

Really sorry I just realised this optimization may not be sound:

The builtin call specializations only check for that the builtin tp flags match, I don't think they check for tp_version_tag and such. So we can have a method that changes its tp_slots under our feet.

Sorry for taking up your time!

The rewriting that we discussed might still pay off though (rewriting {}.get() to a custom uop for example).

That should also be sound, provided we have the correct guards.

I think this is safe: let me explain why:

1. PyMethodDescrObjects are immutable (as Kumar pointed out).
2. type version tags are unique (unless they overflow, which is pretty unlikely as they have limits now).
3. _GUARD_TYPE_VERSION and the type watcher later implies the type and thus method transitively later on.
   TLDR: This is safe on the invariant that LOAD_ATTR guards itself, and all known information is sourced from there to optimize the calls.

Microbenchmark results of calling bunch of methods on each type: