[llvm] [DebugInfo][LoopDistribute] Salvage debug values using dead instructions in the distributed loops (PR #137124)

[Shan Huang via llvm-commits]

Apochens wrote:

Thanks @OCHyams ! I've refined the regression test by removing some instructions and checks in it. As a result, the test is more concise now.

https://github.com/llvm/llvm-project/pull/137124