[llvm] [TableGen] Add a field to filter out GenericTable entries (PR #65458)

[Simon Tatham via llvm-commits]

https://github.com/statham-arm requested changes to this pull request.

The change looks OK to me, but this should surely have a test in `llvm/test/TableGen`.

You don't say what the use case for this is. I'm guessing it might be so you can construct two `GenericTable`s with the same `FilterClass`, so that they select from the same overall set of records, but assign them different `FilterClassField` values so that they include different subsets of the records of that class?

Perhaps demonstrating that in the new test would be a good idea, and maybe mentioning it in the documentation too. (Documentation is at least as much for "what feature can I use to do this thing?" as "what does this feature do?")

https://github.com/llvm/llvm-project/pull/65458