[llvm] [AMDGPU] BackOffBarrier feature added to gfx1250; Removed incorrect "DS Store drain" check. (PR #179818)

[Jay Foad via llvm-commits]

jayfoad wrote:

> I may be misremembering, but didn't you mention BackOffBarrier was not necessary on gfx12.5 because of the split barriers ?

That sounds backwards. BackOffBarrier means that the hardware can properly handle a page fault when waiting at a barrier, and hardware with split barriers should be able to do that.

> I think it is because of how the feature is used in the compiler; we use it to tell whether we need a wait before a barrier signal. Maybe we should rename this feature eventually or split it up ?

Maybe invert it to CannotBackOffBarrier, so that only the old architectures that need the "workaround" of adding a wait before a barrier need the feature?

https://github.com/llvm/llvm-project/pull/179818