[llvm] [LV] Add support for cmp reductions with decreasing IVs. (PR #140451)

[Ramkumar Ramachandra via llvm-commits]

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@@ -269,22 +278,35 @@ class RecurrenceDescriptor {
   /// Returns true if recurrece kind is a signed redux kind.
   static bool isSignedRecurrenceKind(RecurKind Kind) {
     return Kind == RecurKind::SMax || Kind == RecurKind::SMin ||
+           Kind == RecurKind::FindFirstIVSMin ||
            Kind == RecurKind::FindLastIVSMax;
   }
 
+  /// Returns true if the recurrence kind is of the form
+  ///   select(cmp(),x,y) where one of (x,y) is an increasing or decreasing loop
+  ///   induction.
+  static bool isFindIVRecurrenceKind(RecurKind Kind) {
+    return isFindFirstIVRecurrenceKind(Kind) ||
+           isFindLastIVRecurrenceKind(Kind);
+  }
+
   /// 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 for FindLastIV recurrences to replace the start
-  /// value.
+  /// Returns the sentinel value for FindFirstIV &FindLastIV recurrences to
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artagnon wrote:

```suggestion
  /// Returns the sentinel value for FindFirstIV & FindLastIV recurrences to
```

https://github.com/llvm/llvm-project/pull/140451