[llvm] [Target] Add target-independent TargetVerifier dispatcher (PR #205703)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

I'm still not sure exactly where this is going. If this is a true "verifier", I think this is moving in the wrong direction. IR verification should not depend on building the target / codegen. This makes the verification rules build configuration dependent, which is not a good property. The verifier should be enforcing structural rules, which need to be universal. There's a narrow range of IR constructs the target might just want to unconditionally error on, but in general I think those would be better served by LLVMContext errors at the point they appear.

There's a narrower range of things I can see unconditionally rejecting, but would be better served by hardcoding triple checks in the verifier.

In general we should be working to pull more information out of the backend that frontend / middle end need access to for IR production, rather than pulling in dependence on codegen.

https://github.com/llvm/llvm-project/pull/205703