[llvm] [VPlan] Introduce ComputeReductionResult VPInstruction opcode. (PR #70253)

[via llvm-commits]

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@@ -397,6 +398,130 @@ Value *VPInstruction::generateInstruction(VPTransformState &State,
     Builder.GetInsertBlock()->getTerminator()->eraseFromParent();
     return CondBr;
   }
+  case VPInstruction::ComputeReductionResult: {
+    if (Part != 0)
+      return State.get(this, 0);
+
+    // FIXME: The cross-recipe dependency on VPReductionPHIRecipe is temporary
+    // and will be removed by breaking up the recipe further.
+    auto *PhiR = dyn_cast<VPReductionPHIRecipe>(getOperand(0));
----------------
ayalz wrote:

```suggestion
    auto *PhiR = cast<VPReductionPHIRecipe>(getOperand(0));
```

https://github.com/llvm/llvm-project/pull/70253