[llvm] [VPlan] Add specialized VPValue subclasses for different types (NFC) (PR #172758)

[via llvm-commits]

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@@ -129,11 +126,29 @@ void VPDef::dump() const {
 #endif
 
 VPRecipeBase *VPValue::getDefiningRecipe() {
-  return cast_or_null<VPRecipeBase>(Def);
+  auto *Def = dyn_cast<VPDefValue>(this);
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ayalz wrote:

```suggestion
  auto *DefValue = dyn_cast<VPDefValue>(this);
```
to avoid Def->Def

https://github.com/llvm/llvm-project/pull/172758