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

[Florian Hahn via llvm-commits]

================
@@ -5256,6 +5309,13 @@ LoopVectorizationCostModel::selectInterleaveCount(ElementCount VF,
   if (!isScalarEpilogueAllowed())
     return 1;
 
+  // Do not interleave if EVL is preferred and no User IC is specified.
+  if (useVPIWithVPEVLVectorization()) {
----------------
fhahn wrote:

nit: more explicit to check tail-folding style directly here or rename helper to something like `foldTailWithEVL`?

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