[llvm] [LV] Vectorize selecting last IV of min/max element. (PR #141431)

[via llvm-commits]

================
@@ -2419,6 +2422,10 @@ class VPReductionPHIRecipe : public VPHeaderPHIRecipe,
   /// The phi is part of an ordered reduction. Requires IsInLoop to be true.
   bool IsOrdered;
 
+  /// The phi is part of a multi-use reduction (e.g., used in FindLastIV
+  /// patterns).
----------------
ayalz wrote:

Would be good to note somewhere (TODO? Negative tests?) that a min/max reduction could alternatively feed a FindLastIV reduction by having the compare be used twice (by two selects) rather than the phi be used twice (by a select and min/max intrinsic).

https://github.com/llvm/llvm-project/pull/141431