[llvm] [AMDGPU] Make sort ordering in `AMDGPURewriteAGPRCopyMFMAImpl::eliminateSpillsOfReassignedVGPRs()` strict weak. (PR #162493)

[weiwei chen via llvm-commits]

weiweichen wrote:

> Testcase would be good

sure, any suggestion on how to add a test for this @arsenm ? 🙏 

https://github.com/llvm/llvm-project/pull/162493