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

[Ramkumar Ramachandra via llvm-commits]

================
@@ -259,17 +267,33 @@ class RecurrenceDescriptor {
     return Kind == RecurKind::FindLastIV;
   }
 
+  /// 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 Kind == RecurKind::FindLastIV ||
+           Kind == RecurKind::FindFirstIVUMin ||
+           Kind == RecurKind::FindFirstIVSMin;
+  }
+
   /// 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
+  /// replace the start value.
   Value *getSentinelValue() const {
-    assert(isFindLastIVRecurrenceKind(Kind) && "Unexpected recurrence kind");
----------------
artagnon wrote:

Why strip this assert, and move it to a branch?

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