[llvm] [DirectX] Undo SimplifyCFG by reversing select into if else basic blocks (PR #153858)

[Nikita Popov via llvm-commits]

nikic wrote:

Is there a general constraint that `target("dx.RawBuffer")` cannot be used in select or just with these intrinsics?

I'm wondering if we should be preventing this from happening in the first place if it's a legality constraint. We have https://github.com/llvm/llvm-project/blob/f0967fca04c880e9aabd5be043a85127faabb4c6/llvm/lib/Transforms/Utils/Local.cpp#L3839 to control this and could come up with a way to support target types or target intrinsics in there.

https://github.com/llvm/llvm-project/pull/153858