[llvm] [AMDGPU] Fix GFX1250 hazard: S_SET_VGPR_MSB dropped (PR #184904)

[Stanislav Mekhanoshin via llvm-commits]

https://github.com/rampitec requested changes to this pull request.

I certainly do not like it in its current form. It is spaghetti code predicting what will come next. It is a layer violation. It is a downstream merge disaster. Either move mitigation into the VGPR lowering itself (easy), or change pass ordering and prove nothing will break (hard).

https://github.com/llvm/llvm-project/pull/184904