[llvm] AMDGPU/GFX12: Do not wait unnecessarily before barriers (PR #154970)

[Nicolai Hähnle via llvm-commits]

nhaehnle wrote:

> > I have a slight concern that this could trigger the same kind of problems we have seen on GFX10 and GFX11, which we worked around by removing FeatureBackOffBarrier from them. But if not then this seems fine to me.
> 
> It likely can cause the exact same issue on gfx12 (I'd be very surprised if it didn't), seeing as we had to also disable the BackOffBarrier on downstream for that target. I am working on a proper fix for GFX10/11/12 which will allow us to reenable BackOffBarrier.

Can you elaborate on this? I would expect any issues to ultimately come from incorrect source programs. And yeah, we likely have to add some workarounds if we run into that, but pessimizing everything is just not the right answer here.

https://github.com/llvm/llvm-project/pull/154970