[llvm] [VPlan] Compute blend masks from minimum set of edge masks (PR #184838)

[Luke Lau via llvm-commits]

================

----------------
lukel97 wrote:

This diff comes simplifying a mask like `or(x, not y) --> x`. But `y` is false from the original IR which means keeping the more complex mask. gives `or(x, true) -> True`.  I don't think this will happen in practice as the branch on const will be simplified away before the loop vectorizer. https://github.com/llvm/llvm-project/pull/184816

https://github.com/llvm/llvm-project/pull/184838