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

[Florian Hahn via llvm-commits]

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@@ -193,6 +193,17 @@ 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:
+  ///  * EVL-Phi concretization (makes them concrete)
+  ///  * Replaces fixed-length stepping (branch-on-cond CanonicalIVInc,
+  ///    VectorTripCount) with variable-length stepping (branch-on-cond
+  ///    EVLIVInc, TripCount).
+  static void simplifyEVLIVs(VPlan &Plan);
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fhahn wrote:

Not sure if the name is accurate, EVLIVs aren't really simplified, but the canonical IV is replaced by EVL-based phi?

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