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

[Florian Hahn via llvm-commits]

================
@@ -7559,6 +7583,44 @@ getEpilogueLowering(Function *F, Loop *L, LoopVectorizeHints &Hints,
   return CM_EpilogueAllowed;
 }
 
+/// Determine how to lower the epilogue for the vector epilogue loop.
+/// Check if there are any conflicts that prevent tail-folding the epilogue.
+/// \return CM_EpilogueNotNeededFoldEpilogueTail if epilogue tail-folding
+/// is possible, otherwise CM_EpilogueAllowed.
+static EpilogueLowering
+getEpilogueTailLowering(const LoopVectorizationCostModel &MainCM, const Loop *L,
+                        OptimizationRemarkEmitter *ORE) {
+  // Epilogue TF is only enabled when explicitly requested via command line.
+  if (TailFoldingPolicy != TailFoldingPolicyTy::PreferFoldEpilogueTail)
+    return CM_EpilogueAllowed;
+
+  if (!EnableEpilogueVectorization) {
+    reportVectorizationInfo(
+        "LV: Options conflict, epilogue vectorization is disallowed while "
----------------
fhahn wrote:

I think `reportVectorizationInfo` will already add `LV:`. Might be good to have a test for the remark/debug output 
```suggestion
        "Options conflict, epilogue vectorization is disallowed while "
```

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