[llvm] [LV]: Improve accuracy of calculating remaining iterations of MainLoopVF (PR #156723)

[David Sherwood via llvm-commits]

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david-arm wrote:

Could you regenerate the CHECK lines for this test in a seperate pre-commit patch please? It's not your fault, but it's quite hard to see which test changes are actually related to the code changes.

https://github.com/llvm/llvm-project/pull/156723