[llvm] [AMDGPU][PromoteAlloca] Set !amdgpu.non.volatile if promotion fails (PR #179415)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> @arsenm Given that we can't assume all accesses to addrspace(5) are thread-local, what is a good way to proceed here ? I was thinking of doing something a bit more generic. e.g. add a separate pass to analyze all load/stores in addrspace(5), and if they're thread-local, add some MD to them (e.g. `!amdgpu.thread_private`)


Maybe should be a separate pass, or have attributor do it

https://github.com/llvm/llvm-project/pull/179415