[llvm] AMDGPU: Scratch instructions are trivially disjoint from SMEM and buffer instructions (PR #65287)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > LGTM. Perhaps even better would be to use address space checks (addrspacesMayAlias).
> 
> Part of the point of this is to avoid inspecting the MMO which isn't guaranteed to be there

I know MMOs are _allowed_ to be dropped, but in practice they rarely or never are, so I don't see the problem with relying on them for optimization. If we ever find that optimizations are missed because MMOs are dropped then that's just a QoI issue, and we can try to fix whatever pass dropped them.

https://github.com/llvm/llvm-project/pull/65287