[llvm] [LoopInterchange] Motivating example for interchange enablement. NFC. (PR #171631)

[Ryotaro Kasuga via llvm-commits]

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+; RUN: opt < %s -passes=loop-interchange -cache-line-size=64 -pass-remarks-missed='loop-interchange' -pass-remarks-output=%t -S
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kasuga-fj wrote:

Maybe also adding `-pass-remarks='loop-interchange'` is better to ensure the target loops are actually interchanged.

https://github.com/llvm/llvm-project/pull/171631