[llvm] [SelectionDAG] Add instantiated OPC_CheckType (PR #73283)

[Paul Kirth via llvm-commits]

https://github.com/ilovepi commented:

Thanks for the patch, and RFC. Before lading, lets let the discussion on discourse continue a bit, but overall, I'm very positive on the direction.

I've left a small nit inline that should be addressed.

https://github.com/llvm/llvm-project/pull/73283