[llvm] [VPlan] Fold VPDef into VPRecipeBase (NFC). (PR #174282)

[via llvm-commits]

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@@ -395,12 +395,69 @@ class LLVM_ABI_FOR_TEST VPRecipeBase
   DebugLoc DL;
 
 public:
+  /// An enumeration for keeping track of the concrete subclass of VPRecipeBase
+  /// that is actually instantiated. Values of this enumeration are kept in the
+  /// SubclassID field of the VPRecipeBase objects. They are used for concrete
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ayalz wrote:

So should SubclassID be a field of VPRecipeBase, rather than of VPDef?

https://github.com/llvm/llvm-project/pull/174282