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      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...
     36   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>
    132 LLVM_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 
    141 template<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.
    146 template<class To, class From> struct cast_retty_impl {
    147   typedef To& ret_type;         // Normal case, return Ty&
    148 };
    149 template<class To, class From> struct cast_retty_impl<To, const From> {
    150   typedef const To &ret_type;   // Normal case, return Ty&
    151 };
    152 
    153 template<class To, class From> struct cast_retty_impl<To, From*> {
    154   typedef To* ret_type;         // Pointer arg case, return Ty*
    155 };
    156 
    157 template<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 
    161 template<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 
    166 template<class To, class From, class SimpleFrom>
    167 struct 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 
    174 template<class To, class FromTy>
    175 struct 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 
    180 template<class To, class From>
    181 struct 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 //
    189 template<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 
    198 template<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 
    207 template <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 //
    219 template <class X, class Y>
    220 inline typename std::enable_if<!is_simple_type<Y>::value,
    221                                typename cast_retty<X, const Y>::ret_type>::type
    222 cast(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 
    228 template <class X, class Y>
    229 inline 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 
    235 template <class X, class Y>
    236 inline 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 //
    245 template <class X, class Y>
    246 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
    247     !is_simple_type<Y>::value, 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_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
    257     !is_simple_type<Y>::value, typename cast_retty<X, Y>::ret_type>::type
    258 cast_or_null(Y &Val) {
    259   if (!Val)
    260     return nullptr;
    261   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
    262   return cast<X>(Val);
    263 }
    264 
    265 template <class X, class Y>
    266 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
    267 cast_or_null(Y *Val) {
    268   if (!Val) return nullptr;
    269   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
    270   return cast<X>(Val);
    271 }
    272 
    273 
    274 // dyn_cast<X> - Return the argument parameter cast to the specified type.  This
    275 // casting operator returns null if the argument is of the wrong type, so it can
    276 // be used to test for a type as well as cast if successful.  This should be
    277 // used in the context of an if statement like this:
    278 //
    279 //  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
    280 //
    281 
    282 template <class X, class Y>
    283 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
    284     !is_simple_type<Y>::value, typename cast_retty<X, const Y>::ret_type>::type
    285 dyn_cast(const Y &Val) {
    286   return isa<X>(Val) ? cast<X>(Val) : nullptr;
    287 }
    288 
    289 template <class X, class Y>
    290 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y>::ret_type
    291 dyn_cast(Y &Val) {
    292   return isa<X>(Val) ? cast<X>(Val) : nullptr;
    293 }
    294 
    295 template <class X, class Y>
    296 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
    297 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_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
    306     !is_simple_type<Y>::value, typename cast_retty<X, const Y>::ret_type>::type
    307 dyn_cast_or_null(const Y &Val) {
    308   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
    309 }
    310 
    311 template <class X, class Y>
    312 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename std::enable_if<
    313     !is_simple_type<Y>::value, typename cast_retty<X, Y>::ret_type>::type
    314 dyn_cast_or_null(Y &Val) {
    315   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
    316 }
    317 
    318 template <class X, class Y>
    319 LLVM_ATTRIBUTE_UNUSED_RESULT inline typename cast_retty<X, Y *>::ret_type
    320 dyn_cast_or_null(Y *Val) {
    321   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
    322 }
    323 
    324 } // End llvm namespace
    325 
    326 #endif
    327