[PATCH] D127739: [TableGen] Check if input string of !isa is an instance of record type

[Artem Belevich via Phabricator via llvm-commits]

tra added a comment.

Do you have a practical use case where this feature would be needed?

> TableGen will raise an error if failed to cast

This may be considered to be a feature. If you attempt to cast to a record that does not exist, then arguably something went wrong.

While I generally do agree that we don't have a good way to handle non-existing casts, I'm not convinced that `!isa` is the right place to deal with the issue.
E.g. I may want `!isa<R>(x)` to be false for any 'x' that's not an instance of `R`, even if `x` is a string with a value that matches the name of an existing record of `R`?

If we want/need to check whether a record with a given name exists, then we'll probably need a new operator.
Or, perhaps, we should consider extending `!cast` to accept an additional value to be returned if the cast has failed.


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D127739/new/

https://reviews.llvm.org/D127739