1 //===-- llvm/Support/Casting.h - Allow flexible, checked, casts -*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This file defines the isa<X>(), cast<X>(), dyn_cast<X>(), cast_or_null<X>(), 11 // and dyn_cast_or_null<X>() templates. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_SUPPORT_CASTING_H 16 #define LLVM_SUPPORT_CASTING_H 17 18 #include <cassert> 19 20 namespace llvm { 21 22 //===----------------------------------------------------------------------===// 23 // isa<x> Support Templates 24 //===----------------------------------------------------------------------===// 25 26 // Define a template that can be specialized by smart pointers to reflect the 27 // fact that they are automatically dereferenced, and are not involved with the 28 // template selection process... the default implementation is a noop. 29 // 30 template<typename From> struct simplify_type { 31 typedef From SimpleType; // The real type this represents... 32 33 // An accessor to get the real value... getSimplifiedValuesimplify_type34 static SimpleType &getSimplifiedValue(From &Val) { return Val; } 35 }; 36 37 template<typename From> struct simplify_type<const From> { 38 typedef const From SimpleType; 39 static SimpleType &getSimplifiedValue(const From &Val) { 40 return simplify_type<From>::getSimplifiedValue(static_cast<From&>(Val)); 41 } 42 }; 43 44 // The core of the implementation of isa<X> is here; To and From should be 45 // the names of classes. This template can be specialized to customize the 46 // implementation of isa<> without rewriting it from scratch. 47 template <typename To, typename From> 48 struct isa_impl { 49 static inline bool doit(const From &Val) { 50 return To::classof(&Val); 51 } 52 }; 53 54 template <typename To, typename From> struct isa_impl_cl { 55 static inline bool doit(const From &Val) { 56 return isa_impl<To, From>::doit(Val); 57 } 58 }; 59 60 template <typename To, typename From> struct isa_impl_cl<To, const From> { 61 static inline bool doit(const From &Val) { 62 return isa_impl<To, From>::doit(Val); 63 } 64 }; 65 66 template <typename To, typename From> struct isa_impl_cl<To, From*> { 67 static inline bool doit(const From *Val) { 68 return isa_impl<To, From>::doit(*Val); 69 } 70 }; 71 72 template <typename To, typename From> struct isa_impl_cl<To, const From*> { 73 static inline bool doit(const From *Val) { 74 return isa_impl<To, From>::doit(*Val); 75 } 76 }; 77 78 template <typename To, typename From> struct isa_impl_cl<To, const From*const> { 79 static inline bool doit(const From *Val) { 80 return isa_impl<To, From>::doit(*Val); 81 } 82 }; 83 84 template<typename To, typename From, typename SimpleFrom> 85 struct isa_impl_wrap { 86 // When From != SimplifiedType, we can simplify the type some more by using 87 // the simplify_type template. 88 static bool doit(const From &Val) { 89 return isa_impl_wrap<To, SimpleFrom, 90 typename simplify_type<SimpleFrom>::SimpleType>::doit( 91 simplify_type<From>::getSimplifiedValue(Val)); 92 } 93 }; 94 95 template<typename To, typename FromTy> 96 struct isa_impl_wrap<To, FromTy, FromTy> { 97 // When From == SimpleType, we are as simple as we are going to get. 98 static bool doit(const FromTy &Val) { 99 return isa_impl_cl<To,FromTy>::doit(Val); 100 } 101 }; 102 103 // isa<X> - Return true if the parameter to the template is an instance of the 104 // template type argument. Used like this: 105 // 106 // if (isa<Type>(myVal)) { ... } 107 // 108 template <class X, class Y> 109 inline bool isa(const Y &Val) { 110 return isa_impl_wrap<X, Y, typename simplify_type<Y>::SimpleType>::doit(Val); 111 } 112 113 //===----------------------------------------------------------------------===// 114 // cast<x> Support Templates 115 //===----------------------------------------------------------------------===// 116 117 template<class To, class From> struct cast_retty; 118 119 120 // Calculate what type the 'cast' function should return, based on a requested 121 // type of To and a source type of From. 122 template<class To, class From> struct cast_retty_impl { 123 typedef To& ret_type; // Normal case, return Ty& 124 }; 125 template<class To, class From> struct cast_retty_impl<To, const From> { 126 typedef const To &ret_type; // Normal case, return Ty& 127 }; 128 129 template<class To, class From> struct cast_retty_impl<To, From*> { 130 typedef To* ret_type; // Pointer arg case, return Ty* 131 }; 132 133 template<class To, class From> struct cast_retty_impl<To, const From*> { 134 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 135 }; 136 137 template<class To, class From> struct cast_retty_impl<To, const From*const> { 138 typedef const To* ret_type; // Constant pointer arg case, return const Ty* 139 }; 140 141 142 template<class To, class From, class SimpleFrom> 143 struct cast_retty_wrap { 144 // When the simplified type and the from type are not the same, use the type 145 // simplifier to reduce the type, then reuse cast_retty_impl to get the 146 // resultant type. 147 typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type; 148 }; 149 150 template<class To, class FromTy> 151 struct cast_retty_wrap<To, FromTy, FromTy> { 152 // When the simplified type is equal to the from type, use it directly. 153 typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type; 154 }; 155 156 template<class To, class From> 157 struct cast_retty { 158 typedef typename cast_retty_wrap<To, From, 159 typename simplify_type<From>::SimpleType>::ret_type ret_type; 160 }; 161 162 // Ensure the non-simple values are converted using the simplify_type template 163 // that may be specialized by smart pointers... 164 // 165 template<class To, class From, class SimpleFrom> struct cast_convert_val { 166 // This is not a simple type, use the template to simplify it... 167 static typename cast_retty<To, From>::ret_type doit(const From &Val) { 168 return cast_convert_val<To, SimpleFrom, 169 typename simplify_type<SimpleFrom>::SimpleType>::doit( 170 simplify_type<From>::getSimplifiedValue(Val)); 171 } 172 }; 173 174 template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> { 175 // This _is_ a simple type, just cast it. 176 static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) { 177 typename cast_retty<To, FromTy>::ret_type Res2 178 = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val); 179 return Res2; 180 } 181 }; 182 183 184 185 // cast<X> - Return the argument parameter cast to the specified type. This 186 // casting operator asserts that the type is correct, so it does not return null 187 // on failure. It does not allow a null argument (use cast_or_null for that). 188 // It is typically used like this: 189 // 190 // cast<Instruction>(myVal)->getParent() 191 // 192 template <class X, class Y> 193 inline typename cast_retty<X, Y>::ret_type cast(const Y &Val) { 194 assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!"); 195 return cast_convert_val<X, Y, 196 typename simplify_type<Y>::SimpleType>::doit(Val); 197 } 198 199 // cast_or_null<X> - Functionally identical to cast, except that a null value is 200 // accepted. 201 // 202 template <class X, class Y> 203 inline typename cast_retty<X, Y*>::ret_type cast_or_null(Y *Val) { 204 if (Val == 0) return 0; 205 assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!"); 206 return cast<X>(Val); 207 } 208 209 210 // dyn_cast<X> - Return the argument parameter cast to the specified type. This 211 // casting operator returns null if the argument is of the wrong type, so it can 212 // be used to test for a type as well as cast if successful. This should be 213 // used in the context of an if statement like this: 214 // 215 // if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... } 216 // 217 218 template <class X, class Y> 219 inline typename cast_retty<X, Y>::ret_type dyn_cast(const Y &Val) { 220 return isa<X>(Val) ? cast<X, Y>(Val) : 0; 221 } 222 223 // dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null 224 // value is accepted. 225 // 226 template <class X, class Y> 227 inline typename cast_retty<X, Y*>::ret_type dyn_cast_or_null(Y *Val) { 228 return (Val && isa<X>(Val)) ? cast<X>(Val) : 0; 229 } 230 231 } // End llvm namespace 232 233 #endif 234