[llvm] Reland "[LV]: Teach LV to recursively (de)interleave." (PR #125094)

[Hassnaa Hamdi via llvm-commits]

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hassnaaHamdi wrote:

Initially this test had scalar loop because it requires interleaving factor 4 and it was not allowed.
After the first commit only where interleaving factor 4 is allowed, this test would try to do interleaving and then it would crash because of the problem of disagreement between legacy-based cost model and vplan-based model.
 After the change in second commit (skipping comparing legacy to vplan) the test is not crashing and as a result it could have vectorized loop with interleaving.

https://github.com/llvm/llvm-project/pull/125094