Unit Attribute Handling

[webmiche]

This PR concerns UnitAttrs and how to handle them as I need it to add a llvm.emit_c_interface to a function operation.

Currently, this is primarily a hack that I used to get UnitAttrs through the MLIRConverter, but I think this nicely opens the can of worms that is design decisions around UnitAttrs.

The approach of this PR is an implicit one. Anything that maps a str to None is just a UnitAttr with that name.

Obviously, this does not add any functionality to AttributeDef and just hacks around in the attributes dictionary currently. However, I feel that this might not be too bad, at least not the spirit of it. In my understanding, UnitAttrs are not really something you want to define in an AttributeDef (unless it is as part of an OptAttr), but rather information you want to pass down by just adding some attribute.

On the user-side I have this code:

f = FuncOp.from_region("main", batches, [],
                         Region.from_block_list([body_block]))
f.attributes['llvm.emit_c_interface'] = None

[math-fehr]

Hmm, I'm not sure I really like this approach :/ But it's maybe because I don't understand what is the problem.
My main issue with this solution is that the dictionary can hold both an Attribute and a None. So you can't use dict.get(my_key) to get a key if it exists, since None would be mapped to the UnitAttr.

If we defined a UnitAttr (which has nothing in it), wouldn't that solve the problem? And we can of course have something in the printer to make it look better. That way, your convert_attribute should still work, right?
And of course, we would put the UnitAttr in an OptAttributeDef.

[webmiche]

Yeah, you are right, I overlooked that problem. I will draft a version, that adds a UnitAttr 👍

[webmiche]

If anyone sees a way to make this nicer, please tell me!

[math-fehr]

There should be a print_list method in Printer that should do what you want ;)
That way, you can remove your if not first: self.print(", ")

[webmiche]

Wow, that is way better!

[math-fehr]

Besides my comments, this looks good!

[math-fehr]

There should be a print_list method in Printer that should do what you want ;)
That way, you can remove your if not first: self.print(", ")

[math-fehr]

LGTM, we can squash and merge it if you want!