[llvm] [LV, VP]VP intrinsics support for the Loop Vectorizer + adding new tail-folding mode using EVL. (PR #76172)

[Florian Hahn via llvm-commits]

https://github.com/fhahn commented:

It looks like there's a UBSan failure when running some of the tests (comment inline, looks unrelated to the patch, but the tests need to force a vector width > 1), would be good to check with an UBSan build.

Also, the target-independent tests don't exercise the EVL code path due to missing support for VP intrinsics at the moment AFACIT; I think we need to have them with `RISCV` targets as well, as otherwise some code paths aren't exercised in the EVL code path (e.g. interleave groups, gather/scatter, reverse memory ops, masked ops)

https://github.com/llvm/llvm-project/pull/76172