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 "llvm/Support/Compiler.h"
19 #include "llvm/Support/type_traits.h"
20 #include <cassert>
21 
22 namespace llvm {
23 
24 //===----------------------------------------------------------------------===//
25 //                          isa<x> Support Templates
26 //===----------------------------------------------------------------------===//
27 
28 // Define a template that can be specialized by smart pointers to reflect the
29 // fact that they are automatically dereferenced, and are not involved with the
30 // template selection process...  the default implementation is a noop.
31 //
32 template<typename From> struct simplify_type {
33   typedef       From SimpleType;        // The real type this represents...
34 
35   // An accessor to get the real value...
getSimplifiedValuesimplify_type36   static SimpleType &getSimplifiedValue(From &Val) { return Val; }
37 };
38 
39 template<typename From> struct simplify_type<const From> {
40   typedef typename simplify_type<From>::SimpleType NonConstSimpleType;
41   typedef typename add_const_past_pointer<NonConstSimpleType>::type
42     SimpleType;
43   typedef typename add_lvalue_reference_if_not_pointer<SimpleType>::type
44     RetType;
45   static RetType getSimplifiedValue(const From& Val) {
46     return simplify_type<From>::getSimplifiedValue(const_cast<From&>(Val));
47   }
48 };
49 
50 // The core of the implementation of isa<X> is here; To and From should be
51 // the names of classes.  This template can be specialized to customize the
52 // implementation of isa<> without rewriting it from scratch.
53 template <typename To, typename From, typename Enabler = void>
54 struct isa_impl {
55   static inline bool doit(const From &Val) {
56     return To::classof(&Val);
57   }
58 };
59 
60 /// \brief Always allow upcasts, and perform no dynamic check for them.
61 template <typename To, typename From>
62 struct isa_impl<
63     To, From, typename std::enable_if<std::is_base_of<To, From>::value>::type> {
64   static inline bool doit(const From &) { return true; }
65 };
66 
67 template <typename To, typename From> struct isa_impl_cl {
68   static inline bool doit(const From &Val) {
69     return isa_impl<To, From>::doit(Val);
70   }
71 };
72 
73 template <typename To, typename From> struct isa_impl_cl<To, const From> {
74   static inline bool doit(const From &Val) {
75     return isa_impl<To, From>::doit(Val);
76   }
77 };
78 
79 template <typename To, typename From> struct isa_impl_cl<To, From*> {
80   static inline bool doit(const From *Val) {
81     assert(Val && "isa<> used on a null pointer");
82     return isa_impl<To, From>::doit(*Val);
83   }
84 };
85 
86 template <typename To, typename From> struct isa_impl_cl<To, From*const> {
87   static inline bool doit(const From *Val) {
88     assert(Val && "isa<> used on a null pointer");
89     return isa_impl<To, From>::doit(*Val);
90   }
91 };
92 
93 template <typename To, typename From> struct isa_impl_cl<To, const From*> {
94   static inline bool doit(const From *Val) {
95     assert(Val && "isa<> used on a null pointer");
96     return isa_impl<To, From>::doit(*Val);
97   }
98 };
99 
100 template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
101   static inline bool doit(const From *Val) {
102     assert(Val && "isa<> used on a null pointer");
103     return isa_impl<To, From>::doit(*Val);
104   }
105 };
106 
107 template<typename To, typename From, typename SimpleFrom>
108 struct isa_impl_wrap {
109   // When From != SimplifiedType, we can simplify the type some more by using
110   // the simplify_type template.
111   static bool doit(const From &Val) {
112     return isa_impl_wrap<To, SimpleFrom,
113       typename simplify_type<SimpleFrom>::SimpleType>::doit(
114                           simplify_type<const From>::getSimplifiedValue(Val));
115   }
116 };
117 
118 template<typename To, typename FromTy>
119 struct isa_impl_wrap<To, FromTy, FromTy> {
120   // When From == SimpleType, we are as simple as we are going to get.
121   static bool doit(const FromTy &Val) {
122     return isa_impl_cl<To,FromTy>::doit(Val);
123   }
124 };
125 
126 // isa<X> - Return true if the parameter to the template is an instance of the
127 // template type argument.  Used like this:
128 //
129 //  if (isa<Type>(myVal)) { ... }
130 //
131 template <class X, class Y> LLVM_NODISCARD inline bool isa(const Y &Val) {
132   return isa_impl_wrap<X, const Y,
133                        typename simplify_type<const Y>::SimpleType>::doit(Val);
134 }
135 
136 //===----------------------------------------------------------------------===//
137 //                          cast<x> Support Templates
138 //===----------------------------------------------------------------------===//
139 
140 template<class To, class From> struct cast_retty;
141 
142 
143 // Calculate what type the 'cast' function should return, based on a requested
144 // type of To and a source type of From.
145 template<class To, class From> struct cast_retty_impl {
146   typedef To& ret_type;         // Normal case, return Ty&
147 };
148 template<class To, class From> struct cast_retty_impl<To, const From> {
149   typedef const To &ret_type;   // Normal case, return Ty&
150 };
151 
152 template<class To, class From> struct cast_retty_impl<To, From*> {
153   typedef To* ret_type;         // Pointer arg case, return Ty*
154 };
155 
156 template<class To, class From> struct cast_retty_impl<To, const From*> {
157   typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
158 };
159 
160 template<class To, class From> struct cast_retty_impl<To, const From*const> {
161   typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
162 };
163 
164 
165 template<class To, class From, class SimpleFrom>
166 struct cast_retty_wrap {
167   // When the simplified type and the from type are not the same, use the type
168   // simplifier to reduce the type, then reuse cast_retty_impl to get the
169   // resultant type.
170   typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type;
171 };
172 
173 template<class To, class FromTy>
174 struct cast_retty_wrap<To, FromTy, FromTy> {
175   // When the simplified type is equal to the from type, use it directly.
176   typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type;
177 };
178 
179 template<class To, class From>
180 struct cast_retty {
181   typedef typename cast_retty_wrap<To, From,
182                    typename simplify_type<From>::SimpleType>::ret_type ret_type;
183 };
184 
185 // Ensure the non-simple values are converted using the simplify_type template
186 // that may be specialized by smart pointers...
187 //
188 template<class To, class From, class SimpleFrom> struct cast_convert_val {
189   // This is not a simple type, use the template to simplify it...
190   static typename cast_retty<To, From>::ret_type doit(From &Val) {
191     return cast_convert_val<To, SimpleFrom,
192       typename simplify_type<SimpleFrom>::SimpleType>::doit(
193                           simplify_type<From>::getSimplifiedValue(Val));
194   }
195 };
196 
197 template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
198   // This _is_ a simple type, just cast it.
199   static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
200     typename cast_retty<To, FromTy>::ret_type Res2
201      = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
202     return Res2;
203   }
204 };
205 
206 template <class X> struct is_simple_type {
207   static const bool value =
208       std::is_same<X, typename simplify_type<X>::SimpleType>::value;
209 };
210 
211 // cast<X> - Return the argument parameter cast to the specified type.  This
212 // casting operator asserts that the type is correct, so it does not return null
213 // on failure.  It does not allow a null argument (use cast_or_null for that).
214 // It is typically used like this:
215 //
216 //  cast<Instruction>(myVal)->getParent()
217 //
218 template <class X, class Y>
219 inline typename std::enable_if<!is_simple_type<Y>::value,
220                                typename cast_retty<X, const Y>::ret_type>::type
221 cast(const Y &Val) {
222   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
223   return cast_convert_val<
224       X, const Y, typename simplify_type<const Y>::SimpleType>::doit(Val);
225 }
226 
227 template <class X, class Y>
228 inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
229   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
230   return cast_convert_val<X, Y,
231                           typename simplify_type<Y>::SimpleType>::doit(Val);
232 }
233 
234 template <class X, class Y>
235 inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
236   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
237   return cast_convert_val<X, Y*,
238                           typename simplify_type<Y*>::SimpleType>::doit(Val);
239 }
240 
241 // cast_or_null<X> - Functionally identical to cast, except that a null value is
242 // accepted.
243 //
244 template <class X, class Y>
245 LLVM_NODISCARD inline
246     typename std::enable_if<!is_simple_type<Y>::value,
247                             typename cast_retty<X, const Y>::ret_type>::type
248     cast_or_null(const Y &Val) {
249   if (!Val)
250     return nullptr;
251   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
252   return cast<X>(Val);
253 }
254 
255 template <class X, class Y>
256 LLVM_NODISCARD inline
257     typename std::enable_if<!is_simple_type<Y>::value,
258                             typename cast_retty<X, Y>::ret_type>::type
259     cast_or_null(Y &Val) {
260   if (!Val)
261     return nullptr;
262   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
263   return cast<X>(Val);
264 }
265 
266 template <class X, class Y>
267 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type
268 cast_or_null(Y *Val) {
269   if (!Val) return nullptr;
270   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
271   return cast<X>(Val);
272 }
273 
274 
275 // dyn_cast<X> - Return the argument parameter cast to the specified type.  This
276 // casting operator returns null if the argument is of the wrong type, so it can
277 // be used to test for a type as well as cast if successful.  This should be
278 // used in the context of an if statement like this:
279 //
280 //  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
281 //
282 
283 template <class X, class Y>
284 LLVM_NODISCARD inline
285     typename std::enable_if<!is_simple_type<Y>::value,
286                             typename cast_retty<X, const Y>::ret_type>::type
287     dyn_cast(const Y &Val) {
288   return isa<X>(Val) ? cast<X>(Val) : nullptr;
289 }
290 
291 template <class X, class Y>
292 LLVM_NODISCARD inline typename cast_retty<X, Y>::ret_type dyn_cast(Y &Val) {
293   return isa<X>(Val) ? cast<X>(Val) : nullptr;
294 }
295 
296 template <class X, class Y>
297 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type dyn_cast(Y *Val) {
298   return isa<X>(Val) ? cast<X>(Val) : nullptr;
299 }
300 
301 // dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
302 // value is accepted.
303 //
304 template <class X, class Y>
305 LLVM_NODISCARD inline
306     typename std::enable_if<!is_simple_type<Y>::value,
307                             typename cast_retty<X, const Y>::ret_type>::type
308     dyn_cast_or_null(const Y &Val) {
309   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
310 }
311 
312 template <class X, class Y>
313 LLVM_NODISCARD inline
314     typename std::enable_if<!is_simple_type<Y>::value,
315                             typename cast_retty<X, Y>::ret_type>::type
316     dyn_cast_or_null(Y &Val) {
317   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
318 }
319 
320 template <class X, class Y>
321 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type
322 dyn_cast_or_null(Y *Val) {
323   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
324 }
325 
326 } // End llvm namespace
327 
328 #endif
329