[llvm] [VPlan] Add VPSymbolicValueSC for typed VPValues w/o underlying IR value (PR #130507)

[Mel Chen via llvm-commits]

================
@@ -172,6 +181,10 @@ class VPValue {
   /// Returns true if this VPValue is a live-in, i.e. defined outside the VPlan.
   bool isLiveIn() const { return !hasDefiningRecipe(); }
 
+  bool isSymbolic() const { return SubclassID == VPSymbolicValueSC; }
+
+  Type *getType() const;
----------------
Mel-Chen wrote:

Need some description comments for the 2 functions. 

https://github.com/llvm/llvm-project/pull/130507