[llvm] [LV][EVL] Attach a new metadata on EVL vectorized loops (PR #131000)

[Florian Hahn via llvm-commits]

================
@@ -121,6 +125,12 @@ class LoopVectorizeHints {
     SK_PreferScalable = 1
   };
 
+  enum TailFoldingKind {
+    TFK_Unspecified = -1,
+    /// Tail folding with explicit vector length intrinsics.
+    TFK_EVL = 0
+  };
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fhahn wrote:

Does that mean it would also be possible to set the tail-folding style with the hints?

Might not be a good idea to open a two-way street.

My original suggestion was mostly meant to move it to 

```
 // 2.6. Maintain Loop Hints 
 // Keep all loop hints from the original loop on the vector loop (we'll
```

In LoopVectorize.cpp

https://github.com/llvm/llvm-project/pull/131000