message: Add an error message when HLO casting fails.
diff: @@ -39,7 +39,9 @@ template <class T, EnableIfDerivedFromHlo<T>* = nullptr>
  const T* Cast(const HloInstruction* instruction) {
  CHECK(instruction != nullptr);
  const T* casted = dynamic_cast<const T*>(instruction);
  - CHECK(casted != nullptr);
  + CHECK(casted != nullptr)
  + << "Invalid HloInstruction casting. Destination Type: "
  + << typeid(T).name();
  return casted;
  }
  