[llvm] [ConstantTime][LLVM] Add llvm.ct.select intrinsic with generic SelectionDAG lowering (PR #166702)

[Marvin Häuser via llvm-commits]

mhaeuser wrote:

@statham-arm As for the details, of course. At a high level, I think the question whether this approach scales well or is favourable over one that might better is on-topic. I guess, having been too verbose in my previous comment, my question is: Why this way and not the other?

(And yes, it would still need a bitmask fallback, and the related instructions would also be marked with the secret metadata. This would probably happen at the same point the current isel chooses between CMOV/CSEL/… and branches.)

https://github.com/llvm/llvm-project/pull/166702