[llvm] Spaceship intrinsic for GSoC 2024 (PR #83227)

[Nikita Popov via llvm-commits]

nikic wrote:

> @dtcxzyw gladly! I think it makes sense to split it after completing Stage 2 and landing support in SelectionDAG for the `ThreeWayCmp`. Does that seem reasonable?

I'd recommend making the first patch the change to LangRef, Intrinsics.td and (if necessary) the IR Verifier only, and then follow up with the actual SDAG implementation later. This is the critical-path change that everything else depends on, and LangRef changes tend to involve a lot of bikeshedding.

https://github.com/llvm/llvm-project/pull/83227