Differences between two non-consecutive commits

I hope what I am proposing is not already implemented: I searched, but couldn't find how to do it. (Edit, I'm using gitg 3.30.1)

Often I find myself comparing files between two non-consecutive commits (e.g two branches, or specific commits in the same or different branches). Not just changes from one commit and the previous.

This is useful to see precisely what changed among two commits that are known to work in specific ways (e.g. two tags). It is a sort of bisect, but with less hassle.

I think the feature I'm proposing, along with #202, are important together to enable a smoother way to inspect changes between commits in the same or different files.