While doing something else, I ended up reading parts of setobject.c and I noticed that set_intersection doesn't use _PyObject_HashFast():

Is there a reason for it? I tried replacing it (no unit test fails), and benchmarking both versions (with --pgo enabled) but I couldn't see a difference (probably too much noise, or maybe I didn't try hard enough, probably should try on really big big sets to call that operation many a times). In theory though, it should make sets faster when they have strings (and maybe sets of other types slightly slightly slower but _PyObject_HashFast() is used everywhere else in setobject.c so I think that that tradeoff was considered already).

Linked PRs

• GH-137759:Limit _PyObject_HashFast to dicts keys, rename it, and mark it as Py_ALWAYS_INLINE #137828