text: //===- Casting.h ----------------------------------------------------------===//
  //
  //                             The ONNC Project
  //
  // See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  // This file is borrowed from the LLVM project.
  //===----------------------------------------------------------------------===//
  #ifndef ONNC_SUPPORT_CASTING_H
  #define ONNC_SUPPORT_CASTING_H
  #include <cassert>
  
  namespace onnc {
  
  /// \brief If T is a pointer, just return it. If it is not, return T&.
  template<typename T, typename Enable = void>
  struct add_lvalue_reference_if_not_pointer { typedef T &type; };
  
  template <typename T>
  struct add_lvalue_reference_if_not_pointer<
      T, typename std::enable_if<std::is_pointer<T>::value>::type> {
    typedef T type;
  };
  
  /// \brief If T is a pointer to X, return a pointer to const X. If it is not,
  /// return const T.
  template<typename T, typename Enable = void>
  struct add_const_past_pointer { typedef const T type; };
  
  template <typename T>
  struct add_const_past_pointer<
      T, typename std::enable_if<std::is_pointer<T>::value>::type> {
    typedef const typename std::remove_pointer<T>::type *type;
  };
  
  //===----------------------------------------------------------------------===//
  //                          isa<x> Support Templates
  //===----------------------------------------------------------------------===//
  
  // Define a template that can be specialized by smart pointers to reflect the
  // fact that they are automatically dereferenced, and are not involved with the
  // template selection process...  the default implementation is a noop.
  //
  template<typename From> struct simplify_type {
    typedef       From SimpleType;        // The real type this represents...
  
    // An accessor to get the real value...
    static SimpleType &getSimplifiedValue(From &Val) { return Val; }
  };
  
  template<typename From>
  struct simplify_type<const From>
  {
    typedef typename simplify_type<From>::SimpleType NonConstSimpleType;
    typedef typename add_const_past_pointer<NonConstSimpleType>::type
      SimpleType;
    typedef typename add_lvalue_reference_if_not_pointer<SimpleType>::type
      RetType;
    static RetType getSimplifiedValue(const From& Val) {
      return simplify_type<From>::getSimplifiedValue(const_cast<From&>(Val));
    }
  };
  
  // The core of the implementation of isa<X> is here; To and From should be
  // the names of classes.  This template can be specialized to customize the
  // implementation of isa<> without rewriting it from scratch.
  template <typename To, typename From, typename Enabler = void>
  struct isa_impl {
    static inline bool doit(const From &Val) {
      return To::classof(&Val);
    }
  };
  
  /// \brief Always allow upcasts, and perform no dynamic check for them.
  template <typename To, typename From>
  struct isa_impl<
      To, From, typename std::enable_if<std::is_base_of<To, From>::value>::type> {
    static inline bool doit(const From &) { return true; }
  };
  
  template <typename To, typename From> struct isa_impl_cl {
    static inline bool doit(const From &Val) {
      return isa_impl<To, From>::doit(Val);
    }
  };
  
  template <typename To, typename From> struct isa_impl_cl<To, const From> {
    static inline bool doit(const From &Val) {
      return isa_impl<To, From>::doit(Val);
    }
  };
  
  template <typename To, typename From> struct isa_impl_cl<To, From*> {
    static inline bool doit(const From *Val) {
      assert(Val && "isa<> used on a null pointer");
      return isa_impl<To, From>::doit(*Val);
    }
  };
  
  template <typename To, typename From> struct isa_impl_cl<To, From*const> {
    static inline bool doit(const From *Val) {
      assert(Val && "isa<> used on a null pointer");
      return isa_impl<To, From>::doit(*Val);
    }
  };
  
  template <typename To, typename From> struct isa_impl_cl<To, const From*> {
    static inline bool doit(const From *Val) {
      assert(Val && "isa<> used on a null pointer");
      return isa_impl<To, From>::doit(*Val);
    }
  };
  
  template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
    static inline bool doit(const From *Val) {
      assert(Val && "isa<> used on a null pointer");
      return isa_impl<To, From>::doit(*Val);
    }
  };
  
  template<typename To, typename From, typename SimpleFrom>
  struct isa_impl_wrap {
    // When From != SimplifiedType, we can simplify the type some more by using
    // the simplify_type template.
    static bool doit(const From &Val) {
      return isa_impl_wrap<To, SimpleFrom,
        typename simplify_type<SimpleFrom>::SimpleType>::doit(
                            simplify_type<const From>::getSimplifiedValue(Val));
    }
  };
  
  template<typename To, typename FromTy>
  struct isa_impl_wrap<To, FromTy, FromTy> {
    // When From == SimpleType, we are as simple as we are going to get.
    static bool doit(const FromTy &Val) {
      return isa_impl_cl<To,FromTy>::doit(Val);
    }
  };
  
  // isa<X> - Return true if the parameter to the template is an instance of the
  // template type argument.  Used like this:
  //
  //  if (isa<Type>(myVal)) { ... }
  //
  template <class X, class Y> inline bool isa(const Y &Val) {
    return isa_impl_wrap<X, const Y,
                         typename simplify_type<const Y>::SimpleType>::doit(Val);
  }
  
  //===----------------------------------------------------------------------===//
  //                          cast<x> Support Templates
  //===----------------------------------------------------------------------===//
  
  template<class To, class From> struct cast_retty;
  
  
  // Calculate what type the 'cast' function should return, based on a requested
  // type of To and a source type of From.
  template<class To, class From> struct cast_retty_impl {
    typedef To& ret_type;         // Normal case, return Ty&
  };
  template<class To, class From> struct cast_retty_impl<To, const From> {
    typedef const To &ret_type;   // Normal case, return Ty&
  };
  
  template<class To, class From> struct cast_retty_impl<To, From*> {
    typedef To* ret_type;         // Pointer arg case, return Ty*
  };
  
  template<class To, class From> struct cast_retty_impl<To, const From*> {
    typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
  };
  
  template<class To, class From> struct cast_retty_impl<To, const From*const> {
    typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
  };
  
  
  template<class To, class From, class SimpleFrom>
  struct cast_retty_wrap {
    // When the simplified type and the from type are not the same, use the type
    // simplifier to reduce the type, then reuse cast_retty_impl to get the
    // resultant type.
    typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type;
  };
  
  template<class To, class FromTy>
  struct cast_retty_wrap<To, FromTy, FromTy> {
    // When the simplified type is equal to the from type, use it directly.
    typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type;
  };
  
  template<class To, class From>
  struct cast_retty {
    typedef typename cast_retty_wrap<To, From,
                     typename simplify_type<From>::SimpleType>::ret_type ret_type;
  };
  
  // Ensure the non-simple values are converted using the simplify_type template
  // that may be specialized by smart pointers...
  //
  template<class To, class From, class SimpleFrom> struct cast_convert_val {
    // This is not a simple type, use the template to simplify it...
    static typename cast_retty<To, From>::ret_type doit(From &Val) {
      return cast_convert_val<To, SimpleFrom,
        typename simplify_type<SimpleFrom>::SimpleType>::doit(
                            simplify_type<From>::getSimplifiedValue(Val));
    }
  };
  
  template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
    // This _is_ a simple type, just cast it.
    static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
      typename cast_retty<To, FromTy>::ret_type Res2
       = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
      return Res2;
    }
  };
  
  template <class X> struct is_simple_type {
    static const bool value =
        std::is_same<X, typename simplify_type<X>::SimpleType>::value;
  };
  
  // cast<X> - Return the argument parameter cast to the specified type.  This
  // casting operator asserts that the type is correct, so it does not return null
  // on failure.  It does not allow a null argument (use cast_or_null for that).
  // It is typically used like this:
  //
  //  cast<Instruction>(myVal)->getParent()
  //
  template <class X, class Y>
  inline typename std::enable_if<!is_simple_type<Y>::value,
                                 typename cast_retty<X, const Y>::ret_type>::type
  cast(const Y &Val) {
    assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
    return cast_convert_val<
        X, const Y, typename simplify_type<const Y>::SimpleType>::doit(Val);
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
    assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
    return cast_convert_val<X, Y,
                            typename simplify_type<Y>::SimpleType>::doit(Val);
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
    assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
    return cast_convert_val<X, Y*,
                            typename simplify_type<Y*>::SimpleType>::doit(Val);
  }
  
  // cast_or_null<X> - Functionally identical to cast, except that a null value is
  // accepted.
  //
  template <class X, class Y>
  inline
  typename std::enable_if<!is_simple_type<Y>::value,
                              typename cast_retty<X, const Y>::ret_type>::type
      cast_or_null(const Y &Val) {
    if (!Val)
      return nullptr;
    assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
    return cast<X>(Val);
  }
  
  template <class X, class Y>
  inline
      typename std::enable_if<!is_simple_type<Y>::value,
                              typename cast_retty<X, Y>::ret_type>::type
      cast_or_null(Y &Val) {
    if (!Val)
      return nullptr;
    assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
    return cast<X>(Val);
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y *>::ret_type
  cast_or_null(Y *Val) {
    if (!Val) return nullptr;
    assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
    return cast<X>(Val);
  }
  
  
  // dyn_cast<X> - Return the argument parameter cast to the specified type.  This
  // casting operator returns null if the argument is of the wrong type, so it can
  // be used to test for a type as well as cast if successful.  This should be
  // used in the context of an if statement like this:
  //
  //  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
  //
  
  template <class X, class Y>
  inline
      typename std::enable_if<!is_simple_type<Y>::value,
                              typename cast_retty<X, const Y>::ret_type>::type
      dyn_cast(const Y &Val) {
    return isa<X>(Val) ? cast<X>(Val) : nullptr;
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y>::ret_type dyn_cast(Y &Val) {
    return isa<X>(Val) ? cast<X>(Val) : nullptr;
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y *>::ret_type dyn_cast(Y *Val) {
    return isa<X>(Val) ? cast<X>(Val) : nullptr;
  }
  
  // dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
  // value is accepted.
  //
  template <class X, class Y>
  inline
      typename std::enable_if<!is_simple_type<Y>::value,
                              typename cast_retty<X, const Y>::ret_type>::type
      dyn_cast_or_null(const Y &Val) {
    return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
  }
  
  template <class X, class Y>
  inline
      typename std::enable_if<!is_simple_type<Y>::value,
                              typename cast_retty<X, Y>::ret_type>::type
      dyn_cast_or_null(Y &Val) {
    return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
  }
  
  template <class X, class Y>
  inline typename cast_retty<X, Y *>::ret_type
  dyn_cast_or_null(Y *Val) {
    return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
  }
  
  } // namespace of onnc
  
  #endif
  