[llvm] [LV] Add -fold-epilogue-tail option for tail-folded epilogue (PR #190697)

[Florian Hahn via llvm-commits]

================
@@ -3047,6 +3063,11 @@ LoopVectorizationCostModel::computeMaxVF(ElementCount UserVF, unsigned UserIC) {
       return FixedScalableVFPair::getNone();
 
     break;
+  default:
----------------
fhahn wrote:

Better avoid default and explicitly match `CM_EpilogueNotNeededFoldEpilogueTail`. That way, we get warnings/errors when new/unhandled cases are added
```suggestion
  CM_EpilogueNotNeededFoldEpilogueTail:
```

Maybe also emit a message here, if we don't do so already somewhere else

https://github.com/llvm/llvm-project/pull/190697