[llvm] [VPlan] Create AVL as a phi from TC -> 0 with EVL tail folding (PR #151481)

[Ramkumar Ramachandra via llvm-commits]

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@@ -2379,6 +2381,11 @@ bool VPlanTransforms::tryAddExplicitVectorLength(
       CanonicalIVIncrement->getDebugLoc(), "index.evl.next");
   EVLPhi->addOperand(NextEVLIV);
 
+  VPValue *NextAVL = Builder.createOverflowingOp(
+      Instruction::Sub, {AVLPhi, OpVPEVL}, {/*hasNUW=*/true, /*hasNSW=*/false},
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artagnon wrote:

Can you explain why it has nuw but not nsw?

https://github.com/llvm/llvm-project/pull/151481