[TableGen] Add a field to filter out GenericTable entries

[wangpc-pp]

A field FilterClassField is added to GenericTable class, which
is an optional bit field of FilterClass. If specified, only those
records with this field being true will have corresponding entries
in the table.

[statham-arm]

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 GenericTables 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?")

[wangpc-pp]

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

Thanks! I was planning to add a test but I can't find existed tests for GenericTable. I will try to add one later.

You don't say what the use case for this is. I'm guessing it might be so you can construct two GenericTables 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?

Yes! This can be a scenario! And I posted another PR #65460 to show the usage.

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?")\

Will do, thanks!

[statham-arm]

LGTM, thanks!

[michaelmaitland]

LGTM