[llvm] [AMDGPUAA] Check Type before Taking AddressSpace of a Value (PR #128116)

[via llvm-commits]

Chengjunp wrote:

> Ideally we would not allow alias() to be called with non-pointers in the first place. Do you know where these come from?

Hi @nikic and @arsenm, this was first found when I tried to move all the target specific AA before BasicAA and then a test for AMDGPU backend crashed here when taking the address space of a non-pointer value. After investigation, the actual problem came from a wrong use of alias check in FlattenCFG, and I'm working on a fix [here](https://github.com/llvm/llvm-project/pull/128117). 

With that fix, actually we do not need to make modification here. Maybe we can just add an assertion to make sure only pointer values are passes to `alias` function?

https://github.com/llvm/llvm-project/pull/128116