[llvm] [LV] Skip sentinel value for FindLastIV reductions when start value is provably less than IV start. (PR #141788)

[Ramkumar Ramachandra via llvm-commits]

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@@ -9625,7 +9626,8 @@ void LoopVectorizationPlanner::adjustRecipesForReductions(
       // Adjust the start value for FindLastIV recurrences to use the sentinel
       // value after generating the ResumePhi recipe, which uses the original
       // start value.
-      PhiR->setOperand(0, Plan->getOrAddLiveIn(RdxDesc.getSentinelValue()));
+      if (auto *Sentinel = RdxDesc.getSentinelValue())
+        PhiR->setOperand(0, Plan->getOrAddLiveIn(Sentinel));
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artagnon wrote:

Use the same `&& RdxDesc.getSentinelValue()` as part of the if?

https://github.com/llvm/llvm-project/pull/141788