[llvm] [VPlan] Convert EVL loops to variable-length stepping after dissolution (PR #147222)

[Luke Lau via llvm-commits]

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@@ -209,6 +209,18 @@ struct VPlanTransforms {
   /// Replace loop regions with explicit CFG.
   static void dissolveLoopRegions(VPlan &Plan);
 
+  /// Transform EVL loops to use variable-length stepping after region
+  /// dissolution.
+  ///
+  /// Once loop regions are replaced with explicit CFG, EVL loops can step with
+  /// variable vector lengths instead of fixed lengths. This transformation:
+  ///  * Make EVL-Phi concrete.
+  //   * Remove CanonicalIV and increment.
----------------
lukel97 wrote:

```suggestion
  ///  * Makes EVL-Phi concrete.
  //   * Removes CanonicalIV and increment.
```

https://github.com/llvm/llvm-project/pull/147222