[llvm] [VPlan] Simplify VPBlendRecipes to select instructions (PR #133993)

[Ramkumar Ramachandra via llvm-commits]

================
@@ -928,6 +928,19 @@ InstructionCost VPInstruction::computeCost(ElementCount VF,
     return Ctx.TTI.getVectorInstrCost(Instruction::ExtractElement, VecTy,
                                       Ctx.CostKind);
   }
+  case Instruction::Select: {
+    if (!getUnderlyingValue())
----------------
artagnon wrote:

```suggestion
    if (!isLiveIn() || !getUnderlyingValue())
```

https://github.com/llvm/llvm-project/pull/133993