[red-knot] Separate definitions_by_definition into separate fields

[dcreager]

A minor cleanup that breaks up a HashMap of an enum into separate HashMaps for each variant. (These separate fields were already how this cache was being described in the big comment at the top of the file!)

[MichaReiser]

Is there any other motivation other than that this is how it was described in the comment?

I assume the idea of using a single hash map is to reduce the need for allocations (and make the struct slightly smaller). I don't know if this is a worthwhile trade-off.

[MichaReiser]

It does seem to make codspeed hapy

[dcreager]

Is there any other motivation other than that this is how it was described in the comment?

I assume the idea of using a single hash map is to reduce the need for allocations (and make the struct slightly smaller). I don't know if this is a worthwhile trade-off.

It was partly that and partly that the code seemed cleaner — the enum only existed to be able to fold both cases into a single hashmap, but they really are conceptually different caches that seemed better to store separately. (I would have considered this worthwhile if performance was a wash, but not if it regressed)

[carljm]

Thank you! Yeah I was just trying to reduce the number of hashmaps, but if codspeed is happy with this, it's definitely nicer.