[llvm] [VPlan] Move FOR splice cost into VPInstruction::FirstOrderRecurrenceSplice (PR #129645)

[Mel Chen via llvm-commits]

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@@ -743,6 +743,17 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
     return Ctx.TTI.getArithmeticReductionCost(
         Instruction::Or, cast<VectorType>(VecTy), std::nullopt, Ctx.CostKind);
   }
+  case VPInstruction::FirstOrderRecurrenceSplice: {
+    assert(VF.isVector());
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Mel-Chen wrote:

Need some assertion message here.

https://github.com/llvm/llvm-project/pull/129645