[llvm] [LowerBufferFatPointers] Correctly handle alignment modes (PR #134329)

[Krzysztof Drewniak via llvm-commits]

krzysz00 wrote:

... Huh, I apparently forgot to request reviewers on this code

I think this PR is important for handling non-HSA ABIs (which have stricter alignment requirements) correctly, but also shows why we'll want to get relaxed OOB mode off the subtarget and onto the module.

https://github.com/llvm/llvm-project/pull/134329