[llvm] [RFC] IR: Define noalias.addrspace metadata (PR #102461)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

> Yes, it is only true for the pre sm_70 CUDA `__atomicXXX` builtins, but not true for the post sm_70 and newer CUDA atomics APIs (`cuda::atomic`, `cuda::atomic_ref`) from the `<cuda/atomic>` header in the CUDA Toolkit.

Ah, thanks. It's roughly the same as in SYCL, then, except the other way around: there it's the newer `atomic_ref` that's undefined with the private address space, and it's the older atomics that appear to be implicitly well-defined. When it's two languages that have that same problem, maybe the frontend needs to use more than the language to determine whether to set this metadata.

https://github.com/llvm/llvm-project/pull/102461