[llvm] [SelectionDAG] Add space-optimized forms of OPC_CheckComplexPat (PR #73310)

[Wang Pengcheng via llvm-commits]

wangpc-pp wrote:

> This seems fine to me, and in line with the earlier patches. Would you mind adding some documentation about the change somewhere though? I feel like we should at least have a meta comment somewhere noting that the first 8 numbers are special.

Thanks! I'm working on adding some comments to the opcodes and will create a PR later.

https://github.com/llvm/llvm-project/pull/73310