[llvm] Add test for imperfect loop nest in LoopInterchange (PR #201507)

[Ryotaro Kasuga via llvm-commits]

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kasuga-fj wrote:

```suggestion
; RUN: opt -S -passes='loop-interchange' -loop-interchange-profitabilities=ignore < %s | FileCheck %s
```

Then could you please run `utils/update_test_check.py` on this file? It will generate the transformed result as CHECK directives. This is actually the reason I asked you to split the PR. With this script, we can automatically regenerate the transformed IR, which is useful because it lets us easily see what your change actually affects by comparing the diffs.

As for running the script, the command will something like:
```sh
cd llvm-project/llvm
./utils/update_test_check.py --tool-binary /path/to/your/opt ./test/Transforms/LoopInterchange/imperfect-loop-nest.ll
```

https://github.com/llvm/llvm-project/pull/201507