[llvm] [AMDGPU] Fixed crash in getLastMIForRegion when the region is empty. (PR #168653)

[Dhruva Chakrabarti via llvm-commits]

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dhruvachak wrote:

> Are these exactly the same tests as `machine-scheduler-sink-trivial-remats.mir` just with GCN RP trackers enabled? If so I think it's better to just add new RUN lines to it with a different FileCheck prefix to avoid duplicating the input MIR.

yes, good point. I made the suggested change.

https://github.com/llvm/llvm-project/pull/168653