[llvm] [VPlan] Verify dominance for incoming values of phi-like recipes. (PR #124838)

[via llvm-commits]

================
@@ -3283,6 +3295,48 @@ class VPScalarIVStepsRecipe : public VPRecipeWithIRFlags,
   }
 };
 
+/// Casting from VPRecipeBase -> VPPhiAccessors is supported for all recipe
+/// types implementing VPPhiAccessors.
+template <> struct CastIsPossible<VPPhiAccessors, const VPRecipeBase *> {
+  static inline bool isPossible(const VPRecipeBase *f) {
+    return isa<VPIRPhi, VPHeaderPHIRecipe, VPWidenPHIRecipe, VPPhi>(f);
+  }
+};
+/// Support casting from VPRecipeBase -> VPPhiAccessors, by down-casting to the
+/// recipe types implementing VPPhiAccessors.
+template <>
+struct CastInfo<VPPhiAccessors, const VPRecipeBase *>
+    : public CastIsPossible<VPPhiAccessors, const VPRecipeBase *> {
+
+  using Self = CastInfo<VPPhiAccessors, const VPRecipeBase *>;
+
+  using CastReturnType =
+      typename cast_retty<VPPhiAccessors, VPRecipeBase *>::ret_type;
+
+  static inline VPPhiAccessors *doCast(const VPRecipeBase *R) {
+    return const_cast<VPPhiAccessors *>([R]() -> const VPPhiAccessors * {
+      switch (R->getVPDefID()) {
+      case VPDef::VPInstructionSC:
+        return cast<VPPhi>(R);
+      case VPDef::VPIRInstructionSC:
+        return cast<VPIRPhi>(R);
+      case VPDef::VPWidenPHISC:
+        return cast<VPWidenPHIRecipe>(R);
+      default:
+        return cast<VPHeaderPHIRecipe>(R);
+      }
+    }());
+  }
+
+  static inline VPPhiAccessors *castFailed() { return nullptr; }
+
+  static inline VPPhiAccessors *doCastIfPossible(const VPRecipeBase *f) {
----------------
ayalz wrote:

Where is doCastIfPossible used?

https://github.com/llvm/llvm-project/pull/124838