[mypyc] Implement dict setdefault primitive

[97littleleaf11]

Description

Related issue: mypyc/mypyc#644

• Add a new primitive for Dict.setdefault().
• Move some dict creation primitives to beginning of dict_ops.py for better code structure.

Test Plan

Please refer to the test-data changes

[97littleleaf11]

Failed in mypyc compiled version.

[TH3CHARLie]

The compiled mypy fails usually because the newly added primitive breaks sth. Try to comment out the new op and see if the error disappears. If that's the case, you need to double-check if your implementation matches cpython

[97littleleaf11]

@TH3CHARLie thanks! I just found that the second parameter of setdefaultis optional.

[TH3CHARLie]

Actually for Py_None, you can find none_object in ll_builder to represent that, which means you can build the IR itself without the need for a C wrapper function. But in that way, the two variants of the same op are implemented differently. A better solution would be somehow unify the load_address_op into the op registration.

[JukkaL]

Also test a subclass of dict that overrides setdefault. We should use the overridden method (example where this probably matters: OrderedDict). You can create a dict subclass that overrides setdefault that behaves differently and use that in the test. If this doesn't work correctly right now, you'll probably need to add a helper similar to CPyDict_KeysView that has a generic fallback implementation for dict subclasses.

[JukkaL]

Thanks for the updates, looks good now! This made a microbenchmark I came up with over 2x faster, which is a great result.