[llvm] [LV][NFC] Regen some partial reduction tests (PR #129047)

[David Sherwood via llvm-commits]

david-arm wrote:

> I think the extra work to not stage these changes in git (`git add -p .` is great for this) is worth not testing code blocks that we don't actually care about.

I guess it's just every time the IR changes innocuously due to some vplan transformation or whatever, the tests need to be regenerated and then the developer has to go back and delete the scalar loop for every test, and the more tests we add the more painful this becomes. I think if we don't want auto-generated tests then we should remove the `; NOTE` line from the top of the tests because they aren't autogenerated - they've been manually edited. @fhahn any thoughts?

If there is a simple command-line tool or script that can be run for maintaining these tests it's worth documenting that at the top of the test, since the "NOTE..." line suggests you just run the update_test_checks script.

https://github.com/llvm/llvm-project/pull/129047