[llvm] [DebugInfo][LoopStrengthReduce] Fix missing debug location updates (PR #97519)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

> Note that, for the new phi instruction NewPH, which replaces the old phi PH and the cast ShadowUse, I choose to propagate the debug location of PH to it, because the cast is eliminated according to the optimization semantics.

SGTM - we're replacing two instructions (phi and add) in order to make one redundant, it makes sense that we propagate the locations of the replaced instructions.

> @OCHyams @SLTozer have reviewed more of these, are there any more concerns than out-of-place source locations and potential loss of coverage?

No concern for this patch, LGTM too.

Thanks!

https://github.com/llvm/llvm-project/pull/97519