1 //===- llvm/Support/PointerLikeTypeTraits.h - Pointer Traits ----*- 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 PointerLikeTypeTraits class. This allows data 10 // structures to reason about pointers and other things that are pointer sized. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_SUPPORT_POINTERLIKETYPETRAITS_H 15 #define LLVM_SUPPORT_POINTERLIKETYPETRAITS_H 16 17 #include "llvm/Support/DataTypes.h" 18 #include <cassert> 19 #include <type_traits> 20 21 namespace llvm { 22 23 /// A traits type that is used to handle pointer types and things that are just 24 /// wrappers for pointers as a uniform entity. 25 template <typename T> struct PointerLikeTypeTraits; 26 27 namespace detail { 28 /// A tiny meta function to compute the log2 of a compile time constant. 29 template <size_t N> 30 struct ConstantLog2 31 : std::integral_constant<size_t, ConstantLog2<N / 2>::value + 1> {}; 32 template <> struct ConstantLog2<1> : std::integral_constant<size_t, 0> {}; 33 34 // Provide a trait to check if T is pointer-like. 35 template <typename T, typename U = void> struct HasPointerLikeTypeTraits { 36 static const bool value = false; 37 }; 38 39 // sizeof(T) is valid only for a complete T. 40 template <typename T> 41 struct HasPointerLikeTypeTraits< 42 T, decltype((sizeof(PointerLikeTypeTraits<T>) + sizeof(T)), void())> { 43 static const bool value = true; 44 }; 45 46 template <typename T> struct IsPointerLike { 47 static const bool value = HasPointerLikeTypeTraits<T>::value; 48 }; 49 50 template <typename T> struct IsPointerLike<T *> { 51 static const bool value = true; 52 }; 53 } // namespace detail 54 55 // Provide PointerLikeTypeTraits for non-cvr pointers. 56 template <typename T> struct PointerLikeTypeTraits<T *> { 57 static inline void *getAsVoidPointer(T *P) { return P; } 58 static inline T *getFromVoidPointer(void *P) { return static_cast<T *>(P); } 59 60 static constexpr int NumLowBitsAvailable = 61 detail::ConstantLog2<alignof(T)>::value; 62 }; 63 64 template <> struct PointerLikeTypeTraits<void *> { 65 static inline void *getAsVoidPointer(void *P) { return P; } 66 static inline void *getFromVoidPointer(void *P) { return P; } 67 68 /// Note, we assume here that void* is related to raw malloc'ed memory and 69 /// that malloc returns objects at least 4-byte aligned. However, this may be 70 /// wrong, or pointers may be from something other than malloc. In this case, 71 /// you should specify a real typed pointer or avoid this template. 72 /// 73 /// All clients should use assertions to do a run-time check to ensure that 74 /// this is actually true. 75 static constexpr int NumLowBitsAvailable = 2; 76 }; 77 78 // Provide PointerLikeTypeTraits for const things. 79 template <typename T> struct PointerLikeTypeTraits<const T> { 80 typedef PointerLikeTypeTraits<T> NonConst; 81 82 static inline const void *getAsVoidPointer(const T P) { 83 return NonConst::getAsVoidPointer(P); 84 } 85 static inline const T getFromVoidPointer(const void *P) { 86 return NonConst::getFromVoidPointer(const_cast<void *>(P)); 87 } 88 static constexpr int NumLowBitsAvailable = NonConst::NumLowBitsAvailable; 89 }; 90 91 // Provide PointerLikeTypeTraits for const pointers. 92 template <typename T> struct PointerLikeTypeTraits<const T *> { 93 typedef PointerLikeTypeTraits<T *> NonConst; 94 95 static inline const void *getAsVoidPointer(const T *P) { 96 return NonConst::getAsVoidPointer(const_cast<T *>(P)); 97 } 98 static inline const T *getFromVoidPointer(const void *P) { 99 return NonConst::getFromVoidPointer(const_cast<void *>(P)); 100 } 101 static constexpr int NumLowBitsAvailable = NonConst::NumLowBitsAvailable; 102 }; 103 104 // Provide PointerLikeTypeTraits for uintptr_t. 105 template <> struct PointerLikeTypeTraits<uintptr_t> { 106 static inline void *getAsVoidPointer(uintptr_t P) { 107 return reinterpret_cast<void *>(P); 108 } 109 static inline uintptr_t getFromVoidPointer(void *P) { 110 return reinterpret_cast<uintptr_t>(P); 111 } 112 // No bits are available! 113 static constexpr int NumLowBitsAvailable = 0; 114 }; 115 116 /// Provide suitable custom traits struct for function pointers. 117 /// 118 /// Function pointers can't be directly given these traits as functions can't 119 /// have their alignment computed with `alignof` and we need different casting. 120 /// 121 /// To rely on higher alignment for a specialized use, you can provide a 122 /// customized form of this template explicitly with higher alignment, and 123 /// potentially use alignment attributes on functions to satisfy that. 124 template <int Alignment, typename FunctionPointerT> 125 struct FunctionPointerLikeTypeTraits { 126 static constexpr int NumLowBitsAvailable = 127 detail::ConstantLog2<Alignment>::value; 128 static inline void *getAsVoidPointer(FunctionPointerT P) { 129 assert((reinterpret_cast<uintptr_t>(P) & 130 ~((uintptr_t)-1 << NumLowBitsAvailable)) == 0 && 131 "Alignment not satisfied for an actual function pointer!"); 132 return reinterpret_cast<void *>(P); 133 } 134 static inline FunctionPointerT getFromVoidPointer(void *P) { 135 return reinterpret_cast<FunctionPointerT>(P); 136 } 137 }; 138 139 /// Provide a default specialization for function pointers that assumes 4-byte 140 /// alignment. 141 /// 142 /// We assume here that functions used with this are always at least 4-byte 143 /// aligned. This means that, for example, thumb functions won't work or systems 144 /// with weird unaligned function pointers won't work. But all practical systems 145 /// we support satisfy this requirement. 146 template <typename ReturnT, typename... ParamTs> 147 struct PointerLikeTypeTraits<ReturnT (*)(ParamTs...)> 148 : FunctionPointerLikeTypeTraits<4, ReturnT (*)(ParamTs...)> {}; 149 150 } // end namespace llvm 151 152 #endif 153