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

[Mel Chen via llvm-commits]

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@@ -376,6 +383,9 @@ class RecurrenceDescriptor {
   // Currently only a non-reassociative FAdd can be considered in-order,
   // if it is also the only FAdd in the PHI's use chain.
   bool IsOrdered = false;
+  // True if the reduction PHI has multiple in-loop users. This is relevant
+  // for min/max reductions that are part of a FindLastIV pattern.
+  bool IsPhiMultiUse = false;
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Mel-Chen wrote:

However, this doesn't seem precise enough. If it's a cmp-select form of min/max, it's normal for phi to have more than one user. It should more accurately refer to multiple users outside the recurrence chain.

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