[llvm] [GlobalISel] Remove dead VRegs after instruction selection (PR #73892)

[Amara Emerson via llvm-commits]

https://github.com/aemerson commented:

This unfortunately looks much more intrusive and potentially detrimental to compile time than I expected. Can you collect compile time data? I don't think we can accept this generically if this regresses compile time, given that for most targets this doesn't provide any tangible codegen benefit.

https://github.com/llvm/llvm-project/pull/73892