include/llvm/Support/Casting.h

   1 //===- llvm/Support/Casting.h - Allow flexible, checked, casts --*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the isa<X>(), cast<X>(), dyn_cast<X>(), cast_or_null<X>(),
  10 // and dyn_cast_or_null<X>() templates.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #ifndef LLVM_SUPPORT_CASTING_H
  15 #define LLVM_SUPPORT_CASTING_H
  16
  17 #include "llvm/Support/Compiler.h"
  18 #include "llvm/Support/type_traits.h"
  19 #include <cassert>
  20 #include <memory>
  21 #include <type_traits>
  22
  23 namespace llvm {
  24
  25 //===----------------------------------------------------------------------===//
  26 //                          isa<x> Support Templates
  27 //===----------------------------------------------------------------------===//
  28
  29 // Define a template that can be specialized by smart pointers to reflect the
  30 // fact that they are automatically dereferenced, and are not involved with the
  31 // template selection process...  the default implementation is a noop.
  32 //
  33 template<typename From> struct simplify_type {
  34   using SimpleType = From; // The real type this represents...
  35
  36   // An accessor to get the real value...
  37   static SimpleType &getSimplifiedValue(From &Val) { return Val; }
  38 };
  39
  40 template<typename From> struct simplify_type<const From> {
  41   using NonConstSimpleType = typename simplify_type<From>::SimpleType;
  42   using SimpleType =
  43       typename add_const_past_pointer<NonConstSimpleType>::type;
  44   using RetType =
  45       typename add_lvalue_reference_if_not_pointer<SimpleType>::type;
  46
  47   static RetType getSimplifiedValue(const From& Val) {
  48     return simplify_type<From>::getSimplifiedValue(const_cast<From&>(Val));
  49   }
  50 };
  51
  52 // The core of the implementation of isa<X> is here; To and From should be
  53 // the names of classes.  This template can be specialized to customize the
  54 // implementation of isa<> without rewriting it from scratch.
  55 template <typename To, typename From, typename Enabler = void>
  56 struct isa_impl {
  57   static inline bool doit(const From &Val) {
  58     return To::classof(&Val);
  59   }
  60 };
  61
  62 /// Always allow upcasts, and perform no dynamic check for them.
  63 template <typename To, typename From>
  64 struct isa_impl<
  65     To, From, typename std::enable_if<std::is_base_of<To, From>::value>::type> {
  66   static inline bool doit(const From &) { return true; }
  67 };
  68
  69 template <typename To, typename From> struct isa_impl_cl {
  70   static inline bool doit(const From &Val) {
  71     return isa_impl<To, From>::doit(Val);
  72   }
  73 };
  74
  75 template <typename To, typename From> struct isa_impl_cl<To, const From> {
  76   static inline bool doit(const From &Val) {
  77     return isa_impl<To, From>::doit(Val);
  78   }
  79 };
  80
  81 template <typename To, typename From>
  82 struct isa_impl_cl<To, const std::unique_ptr<From>> {
  83   static inline bool doit(const std::unique_ptr<From> &Val) {
  84     assert(Val && "isa<> used on a null pointer");
  85     return isa_impl_cl<To, From>::doit(*Val);
  86   }
  87 };
  88
  89 template <typename To, typename From> struct isa_impl_cl<To, From*> {
  90   static inline bool doit(const From *Val) {
  91     assert(Val && "isa<> used on a null pointer");
  92     return isa_impl<To, From>::doit(*Val);
  93   }
  94 };
  95
  96 template <typename To, typename From> struct isa_impl_cl<To, From*const> {
  97   static inline bool doit(const From *Val) {
  98     assert(Val && "isa<> used on a null pointer");
  99     return isa_impl<To, From>::doit(*Val);
 100   }
 101 };
 102
 103 template <typename To, typename From> struct isa_impl_cl<To, const From*> {
 104   static inline bool doit(const From *Val) {
 105     assert(Val && "isa<> used on a null pointer");
 106     return isa_impl<To, From>::doit(*Val);
 107   }
 108 };
 109
 110 template <typename To, typename From> struct isa_impl_cl<To, const From*const> {
 111   static inline bool doit(const From *Val) {
 112     assert(Val && "isa<> used on a null pointer");
 113     return isa_impl<To, From>::doit(*Val);
 114   }
 115 };
 116
 117 template<typename To, typename From, typename SimpleFrom>
 118 struct isa_impl_wrap {
 119   // When From != SimplifiedType, we can simplify the type some more by using
 120   // the simplify_type template.
 121   static bool doit(const From &Val) {
 122     return isa_impl_wrap<To, SimpleFrom,
 123       typename simplify_type<SimpleFrom>::SimpleType>::doit(
 124                           simplify_type<const From>::getSimplifiedValue(Val));
 125   }
 126 };
 127
 128 template<typename To, typename FromTy>
 129 struct isa_impl_wrap<To, FromTy, FromTy> {
 130   // When From == SimpleType, we are as simple as we are going to get.
 131   static bool doit(const FromTy &Val) {
 132     return isa_impl_cl<To,FromTy>::doit(Val);
 133   }
 134 };
 135
 136 // isa<X> - Return true if the parameter to the template is an instance of the
 137 // template type argument.  Used like this:
 138 //
 139 //  if (isa<Type>(myVal)) { ... }
 140 //
 141 template <class X, class Y> LLVM_NODISCARD inline bool isa(const Y &Val) {
 142   return isa_impl_wrap<X, const Y,
 143                        typename simplify_type<const Y>::SimpleType>::doit(Val);
 144 }
 145
 146 //===----------------------------------------------------------------------===//
 147 //                          cast<x> Support Templates
 148 //===----------------------------------------------------------------------===//
 149
 150 template<class To, class From> struct cast_retty;
 151
 152 // Calculate what type the 'cast' function should return, based on a requested
 153 // type of To and a source type of From.
 154 template<class To, class From> struct cast_retty_impl {
 155   using ret_type = To &;       // Normal case, return Ty&
 156 };
 157 template<class To, class From> struct cast_retty_impl<To, const From> {
 158   using ret_type = const To &; // Normal case, return Ty&
 159 };
 160
 161 template<class To, class From> struct cast_retty_impl<To, From*> {
 162   using ret_type = To *;       // Pointer arg case, return Ty*
 163 };
 164
 165 template<class To, class From> struct cast_retty_impl<To, const From*> {
 166   using ret_type = const To *; // Constant pointer arg case, return const Ty*
 167 };
 168
 169 template<class To, class From> struct cast_retty_impl<To, const From*const> {
 170   using ret_type = const To *; // Constant pointer arg case, return const Ty*
 171 };
 172
 173 template <class To, class From>
 174 struct cast_retty_impl<To, std::unique_ptr<From>> {
 175 private:
 176   using PointerType = typename cast_retty_impl<To, From *>::ret_type;
 177   using ResultType = typename std::remove_pointer<PointerType>::type;
 178
 179 public:
 180   using ret_type = std::unique_ptr<ResultType>;
 181 };
 182
 183 template<class To, class From, class SimpleFrom>
 184 struct cast_retty_wrap {
 185   // When the simplified type and the from type are not the same, use the type
 186   // simplifier to reduce the type, then reuse cast_retty_impl to get the
 187   // resultant type.
 188   using ret_type = typename cast_retty<To, SimpleFrom>::ret_type;
 189 };
 190
 191 template<class To, class FromTy>
 192 struct cast_retty_wrap<To, FromTy, FromTy> {
 193   // When the simplified type is equal to the from type, use it directly.
 194   using ret_type = typename cast_retty_impl<To,FromTy>::ret_type;
 195 };
 196
 197 template<class To, class From>
 198 struct cast_retty {
 199   using ret_type = typename cast_retty_wrap<
 200       To, From, typename simplify_type<From>::SimpleType>::ret_type;
 201 };
 202
 203 // Ensure the non-simple values are converted using the simplify_type template
 204 // that may be specialized by smart pointers...
 205 //
 206 template<class To, class From, class SimpleFrom> struct cast_convert_val {
 207   // This is not a simple type, use the template to simplify it...
 208   static typename cast_retty<To, From>::ret_type doit(From &Val) {
 209     return cast_convert_val<To, SimpleFrom,
 210       typename simplify_type<SimpleFrom>::SimpleType>::doit(
 211                           simplify_type<From>::getSimplifiedValue(Val));
 212   }
 213 };
 214
 215 template<class To, class FromTy> struct cast_convert_val<To,FromTy,FromTy> {
 216   // This _is_ a simple type, just cast it.
 217   static typename cast_retty<To, FromTy>::ret_type doit(const FromTy &Val) {
 218     typename cast_retty<To, FromTy>::ret_type Res2
 219      = (typename cast_retty<To, FromTy>::ret_type)const_cast<FromTy&>(Val);
 220     return Res2;
 221   }
 222 };
 223
 224 template <class X> struct is_simple_type {
 225   static const bool value =
 226       std::is_same<X, typename simplify_type<X>::SimpleType>::value;
 227 };
 228
 229 // cast<X> - Return the argument parameter cast to the specified type.  This
 230 // casting operator asserts that the type is correct, so it does not return null
 231 // on failure.  It does not allow a null argument (use cast_or_null for that).
 232 // It is typically used like this:
 233 //
 234 //  cast<Instruction>(myVal)->getParent()
 235 //
 236 template <class X, class Y>
 237 inline typename std::enable_if<!is_simple_type<Y>::value,
 238                                typename cast_retty<X, const Y>::ret_type>::type
 239 cast(const Y &Val) {
 240   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
 241   return cast_convert_val<
 242       X, const Y, typename simplify_type<const Y>::SimpleType>::doit(Val);
 243 }
 244
 245 template <class X, class Y>
 246 inline typename cast_retty<X, Y>::ret_type cast(Y &Val) {
 247   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
 248   return cast_convert_val<X, Y,
 249                           typename simplify_type<Y>::SimpleType>::doit(Val);
 250 }
 251
 252 template <class X, class Y>
 253 inline typename cast_retty<X, Y *>::ret_type cast(Y *Val) {
 254   assert(isa<X>(Val) && "cast<Ty>() argument of incompatible type!");
 255   return cast_convert_val<X, Y*,
 256                           typename simplify_type<Y*>::SimpleType>::doit(Val);
 257 }
 258
 259 template <class X, class Y>
 260 inline typename cast_retty<X, std::unique_ptr<Y>>::ret_type
 261 cast(std::unique_ptr<Y> &&Val) {
 262   assert(isa<X>(Val.get()) && "cast<Ty>() argument of incompatible type!");
 263   using ret_type = typename cast_retty<X, std::unique_ptr<Y>>::ret_type;
 264   return ret_type(
 265       cast_convert_val<X, Y *, typename simplify_type<Y *>::SimpleType>::doit(
 266           Val.release()));
 267 }
 268
 269 // cast_or_null<X> - Functionally identical to cast, except that a null value is
 270 // accepted.
 271 //
 272 template <class X, class Y>
 273 LLVM_NODISCARD inline
 274     typename std::enable_if<!is_simple_type<Y>::value,
 275                             typename cast_retty<X, const Y>::ret_type>::type
 276     cast_or_null(const Y &Val) {
 277   if (!Val)
 278     return nullptr;
 279   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
 280   return cast<X>(Val);
 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, Y>::ret_type>::type
 287     cast_or_null(Y &Val) {
 288   if (!Val)
 289     return nullptr;
 290   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
 291   return cast<X>(Val);
 292 }
 293
 294 template <class X, class Y>
 295 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type
 296 cast_or_null(Y *Val) {
 297   if (!Val) return nullptr;
 298   assert(isa<X>(Val) && "cast_or_null<Ty>() argument of incompatible type!");
 299   return cast<X>(Val);
 300 }
 301
 302 template <class X, class Y>
 303 inline typename cast_retty<X, std::unique_ptr<Y>>::ret_type
 304 cast_or_null(std::unique_ptr<Y> &&Val) {
 305   if (!Val)
 306     return nullptr;
 307   return cast<X>(std::move(Val));
 308 }
 309
 310 // dyn_cast<X> - Return the argument parameter cast to the specified type.  This
 311 // casting operator returns null if the argument is of the wrong type, so it can
 312 // be used to test for a type as well as cast if successful.  This should be
 313 // used in the context of an if statement like this:
 314 //
 315 //  if (const Instruction *I = dyn_cast<Instruction>(myVal)) { ... }
 316 //
 317
 318 template <class X, class Y>
 319 LLVM_NODISCARD inline
 320     typename std::enable_if<!is_simple_type<Y>::value,
 321                             typename cast_retty<X, const Y>::ret_type>::type
 322     dyn_cast(const Y &Val) {
 323   return isa<X>(Val) ? cast<X>(Val) : nullptr;
 324 }
 325
 326 template <class X, class Y>
 327 LLVM_NODISCARD inline typename cast_retty<X, Y>::ret_type dyn_cast(Y &Val) {
 328   return isa<X>(Val) ? cast<X>(Val) : nullptr;
 329 }
 330
 331 template <class X, class Y>
 332 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type dyn_cast(Y *Val) {
 333   return isa<X>(Val) ? cast<X>(Val) : nullptr;
 334 }
 335
 336 // dyn_cast_or_null<X> - Functionally identical to dyn_cast, except that a null
 337 // value is accepted.
 338 //
 339 template <class X, class Y>
 340 LLVM_NODISCARD inline
 341     typename std::enable_if<!is_simple_type<Y>::value,
 342                             typename cast_retty<X, const Y>::ret_type>::type
 343     dyn_cast_or_null(const Y &Val) {
 344   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
 345 }
 346
 347 template <class X, class Y>
 348 LLVM_NODISCARD inline
 349     typename std::enable_if<!is_simple_type<Y>::value,
 350                             typename cast_retty<X, Y>::ret_type>::type
 351     dyn_cast_or_null(Y &Val) {
 352   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
 353 }
 354
 355 template <class X, class Y>
 356 LLVM_NODISCARD inline typename cast_retty<X, Y *>::ret_type
 357 dyn_cast_or_null(Y *Val) {
 358   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
 359 }
 360
 361 // unique_dyn_cast<X> - Given a unique_ptr<Y>, try to return a unique_ptr<X>,
 362 // taking ownership of the input pointer iff isa<X>(Val) is true.  If the
 363 // cast is successful, From refers to nullptr on exit and the casted value
 364 // is returned.  If the cast is unsuccessful, the function returns nullptr
 365 // and From is unchanged.
 366 template <class X, class Y>
 367 LLVM_NODISCARD inline auto unique_dyn_cast(std::unique_ptr<Y> &Val)
 368     -> decltype(cast<X>(Val)) {
 369   if (!isa<X>(Val))
 370     return nullptr;
 371   return cast<X>(std::move(Val));
 372 }
 373
 374 template <class X, class Y>
 375 LLVM_NODISCARD inline auto unique_dyn_cast(std::unique_ptr<Y> &&Val)
 376     -> decltype(cast<X>(Val)) {
 377   return unique_dyn_cast<X, Y>(Val);
 378 }
 379
 380 // dyn_cast_or_null<X> - Functionally identical to unique_dyn_cast, except that
 381 // a null value is accepted.
 382 template <class X, class Y>
 383 LLVM_NODISCARD inline auto unique_dyn_cast_or_null(std::unique_ptr<Y> &Val)
 384     -> decltype(cast<X>(Val)) {
 385   if (!Val)
 386     return nullptr;
 387   return unique_dyn_cast<X, Y>(Val);
 388 }
 389
 390 template <class X, class Y>
 391 LLVM_NODISCARD inline auto unique_dyn_cast_or_null(std::unique_ptr<Y> &&Val)
 392     -> decltype(cast<X>(Val)) {
 393   return unique_dyn_cast_or_null<X, Y>(Val);
 394 }
 395
 396 } // end namespace llvm
 397
 398 #endif // LLVM_SUPPORT_CASTING_H