[llvm] [AMDGPU] Add function attribute to control TBUFFER combining (PR #156454)

[Piotr Sobczak via llvm-commits]

piotrAMD wrote:

> Also I'm still not clear how this differs from the the relaxed-oob-mode feature. Can these be merged into one? In any case I'd like to see those use identical mechanisms before introducing another knob

This is similar to the existing relaxed-oob-mode feature in that that it controls oob merging behaviour. The behavior for untyped buffer merging (in llvm-ir) and this tbuffer merging in mir are driven by different language features, so we need to be able to select them individually.
When I added relaxed-oob-mode I was not aware about the tbuffer problem that Harrison found.

I guess having a single mechanism like multistate function attribute/module flag would be ok, but there is this problem that the function that uses relaxed-oob-mode currently (`AllowsMisalignedMemoryAccesses()`) has no access to "Function", and I am not sure what the best solution for that one is.


https://github.com/llvm/llvm-project/pull/156454