[llvm] [AMDGPU][Verifier] Check address space of `alloca` instruction (PR #135820)

[Shilei Tian via llvm-commits]

shiltian wrote:

> I have another implementation of this but I was actually thinking we could relax this restriction, and just lower 0 alloca as alloca + addrspacecast. It would avoid a common bug report and isn't that horrible. We could use a nicer version of the PTX hack, where infer address spaces can assume the addrspace but it wouldn't be a hard requirement

Doesn't it violate LLVM IR semantics since we treat a AS 0 type _as_ AS5?

https://github.com/llvm/llvm-project/pull/135820