[llvm] [AMDGPU] Improve detection of non-null addrspacecast operands (PR #82311)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Ideally we would fix this by adding proper non-0 null pointer support throughout the IR; this is just a backend hack 

https://github.com/llvm/llvm-project/pull/82311