[llvm] [LoopInterchange] Support inner-loop simple reductions via UndoSimpleReduction (PR #172970)

[Ryotaro Kasuga via llvm-commits]

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kasuga-fj wrote:

Consider adding more cases, e.g., `MemRef` doesn't dominate `ExitBlock` (i.e., line 1192).

https://github.com/llvm/llvm-project/pull/172970