[llvm] [SelectionDAG] Look through addrspacecasts when raising stack object alignment (PR #201772)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm requested changes to this pull request.

I think the PTX alloca handling should be changed. Ideally the datalayout and whole stack would be changed to use the natural address space in the first place. Short of that, it would still be possible to modify NVPTXLowerAlloca to replace the original addrspace 0 allocas with the correct address space instead of inserting cast pairs 

https://github.com/llvm/llvm-project/pull/201772