[llvm] Adding the support for vectorization of loops with load based tripcount (PR #209390)

[Ramkumar Ramachandra via llvm-commits]

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artagnon wrote:

It's currently a bit difficult to review this PR as it touches three different parts: can you kindly ping on the three different PRs? You can keep this PR as a draft showing the end result?

https://github.com/llvm/llvm-project/pull/209390