[llvm] [LV] Keep predicate select when optimizeFindIVReductions when folding tail. (PR #191166)

[Luke Lau via llvm-commits]

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@@ -5880,6 +5880,15 @@ void VPlanTransforms::optimizeFindIVReductions(VPlan &Plan,
         continue;
     }
 
+    // When tail folding, mask the condition with the header mask to prevent
+    // propagating poison from inactive lanes in the last vector iteration.
+    if (HeaderMask) {
+      VPBuilder LoopBuilder(FindLastSelect->getDefiningRecipe());
+      auto *Or = LoopBuilder.createLogicalAnd(HeaderMask,
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lukel97 wrote:

Should this just set Cond directly? That way we wouldn't need the extra select in the middle block. And I think it would also mean we don't need to fix up the AnyOf for EVL tail folding

https://github.com/llvm/llvm-project/pull/191166