Casting.h revision 36b56886974eae4f9c5ebc96befd3e7bfe5de338 
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
22namespace 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//
32template<typename From> struct simplify_type {
33  typedef       From SimpleType;        // The real type this represents...
34
35  // An accessor to get the real value...
36  static SimpleType &getSimplifiedValue(From &Val) { return Val; }
37};
38
39template<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.
53template <typename To, typename From, typename Enabler = void>
54struct 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.
61template <typename To, typename From>
62struct 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
67template <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
73template <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
79template <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
86template <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
93template <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
100template <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
107template<typename To, typename From, typename SimpleFrom>
108struct 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
118template<typename To, typename FromTy>
119struct 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//
131template <class X, class Y>
132LLVM_ATTRIBUTE_UNUSED_RESULT inline bool isa(const Y &Val) {
133  return isa_impl_wrap<X, const Y,
134                       typename simplify_type<const Y>::SimpleType>::doit(Val);
135}
136
137//===----------------------------------------------------------------------===//
138//                          cast<x> Support Templates
139//===----------------------------------------------------------------------===//
140
141template<class To, class From> struct cast_retty;
142
143
144// Calculate what type the 'cast' function should return, based on a requested
145// type of To and a source type of From.
146template<class To, class From> struct cast_retty_impl {
147  typedef To& ret_type;         // Normal case, return Ty&
148};
149template<class To, class From> struct cast_retty_impl<To, const From> {
150  typedef const To &ret_type;   // Normal case, return Ty&
151};
152
153template<class To, class From> struct cast_retty_impl<To, From*> {
154  typedef To* ret_type;         // Pointer arg case, return Ty*
155};
156
157template<class To, class From> struct cast_retty_impl<To, const From*> {
158  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
159};
160
161template<class To, class From> struct cast_retty_impl<To, const From*const> {
162  typedef const To* ret_type;   // Constant pointer arg case, return const Ty*
163};
164
165
166template<class To, class From, class SimpleFrom>
167struct cast_retty_wrap {
168  // When the simplified type and the from type are not the same, use the type
169  // simplifier to reduce the type, then reuse cast_retty_impl to get the
170  // resultant type.
171  typedef typename cast_retty<To, SimpleFrom>::ret_type ret_type;
172};
173
174template<class To, class FromTy>
175struct cast_retty_wrap<To, FromTy, FromTy> {
176  // When the simplified type is equal to the from type, use it directly.
177  typedef typename cast_retty_impl<To,FromTy>::ret_type ret_type;
178};
179
180template<class To, class From>
181struct cast_retty {
182  typedef typename cast_retty_wrap<To, From,
183                   typename simplify_type<From>::SimpleType>::ret_type ret_type;
184};
185
186// Ensure the non-simple values are converted using the simplify_type template
187// that may be specialized by smart pointers...
188//
189template<class To, class From, class SimpleFrom> struct cast_convert_val {
190  // This is not a simple type, use the template to simplify it...
191  static typename cast_retty<To, From>::ret_type doit(From &Val) {
192    return cast_convert_val<To, SimpleFrom,
193      typename simplify_type<SimpleFrom>::SimpleType>::doit(
194                          simplify_type<From>::getSimplifiedValue(Val));
195  }
196};
197
198template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
199  // This _is_ a simple type, just cast it.
200  static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
201    typename cast_retty<To, FromTy>::ret_type Res2
202     = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
203    return Res2;
204  }
205};
206
207template <class X> struct is_simple_type {
208  static const bool value =
209      std::is_same<X, typename simplify_type<X>::SimpleType>::value;
210};
211
212// cast<X> - Return the argument parameter cast to the specified type.  This
213// casting operator asserts that the type is correct, so it does not return null
214// on failure.  It does not allow a null argument (use cast_or_null for that).
215// It is typically used like this:
216//
217//  cast<Instruction>(myVal)->getParent()
218//
219template <class X, class Y>
220inline typename std::enable_if<!is_simple_type<Y>::value,
221                               typename cast_retty<X, const Y>::ret_type>::type
222cast(const Y &Val) {
223  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
224  return cast_convert_val<
225      X, const Y, typename simplify_type<const Y>::SimpleType>::doit(Val);
226}
227
228template <class X, class Y>
229inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
230  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
231  return cast_convert_val<X, Y,
232                          typename simplify_type<Y>::SimpleType>::doit(Val);
233}
234
235template <class X, class Y>
236inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
237  assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
238  return cast_convert_val<X, Y*,
239                          typename simplify_type<Y*>::SimpleType>::doit(Val);
240}
241
242// cast_or_null<X> - Functionally identical to cast, except that a null value is
243// accepted.
244//
245template <class X, class Y>
246LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
247cast_or_null(Y *Val) {
248  if (Val == 0) return 0;
249  assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
250  return cast<X>(Val);
251}
252
253
254// dyn_cast<X> - Return the argument parameter cast to the specified type.  This
255// casting operator returns null if the argument is of the wrong type, so it can
256// be used to test for a type as well as cast if successful.  This should be
257// used in the context of an if statement like this:
258//
259//  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
260//
261
262template <class X, class Y>
263LLVM_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
264    !is_simple_type<Y>::value, typename cast_retty<X, const Y>::ret_type>::type
265dyn_cast(const Y &Val) {
266  return isa<X>(Val) ? cast<X>(Val) : 0;
267}
268
269template <class X, class Y>
270LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y>::ret_type
271dyn_cast(Y &Val) {
272  return isa<X>(Val) ? cast<X>(Val) : 0;
273}
274
275template <class X, class Y>
276LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
277dyn_cast(Y *Val) {
278  return isa<X>(Val) ? cast<X>(Val) : 0;
279}
280
281// dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
282// value is accepted.
283//
284template <class X, class Y>
285LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
286dyn_cast_or_null(Y *Val) {
287  return (Val && isa<X>(Val)) ? cast<X>(Val) : 0;
288}
289
290} // End llvm namespace
291
292#endif
293