[llvm] [LoopVectorize] Vectorize select-cmp reduction pattern for increasing integer induction variable (PR #67812)

[Graham Hunter via llvm-commits]

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@@ -236,10 +253,26 @@ class RecurrenceDescriptor {
     return Kind == RecurKind::IAnyOf || Kind == RecurKind::FAnyOf;
   }
 
+  /// Returns true if the recurrence kind is of the form
+  ///   select(cmp(),x,y) where one of (x,y) is increasing loop induction.
+  static bool isFindLastIVRecurrenceKind(RecurKind Kind) {
+    return Kind == RecurKind::IFindLastIV || Kind == RecurKind::FFindLastIV;
+  }
+
   /// Returns the type of the recurrence. This type can be narrower than the
   /// actual type of the Phi if the recurrence has been type-promoted.
   Type *getRecurrenceType() const { return RecurrenceType; }
 
+  /// Returns the sentinel value used to replace the start value.
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huntergr-arm wrote:

nit: Would be nice to clarify that this is a sentinel value specifically for FindLastIV recurrences.

https://github.com/llvm/llvm-project/pull/67812