1 //===--- AlignOf.h - Portable calculation of type alignment -----*- 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 AlignOf function that computes alignments for 11 // arbitrary types. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_SUPPORT_ALIGNOF_H 16 #define LLVM_SUPPORT_ALIGNOF_H 17 18 #include "llvm/Support/Compiler.h" 19 #include <cstddef> 20 21 namespace llvm { 22 template <typename T> 23 struct AlignmentCalcImpl { 24 char x; 25 #if defined(_MSC_VER) 26 // Disables "structure was padded due to __declspec(align())" warnings that are 27 // generated by any class using AlignOf<T> with a manually specified alignment. 28 // Although the warning is disabled in the LLVM project we need this pragma 29 // as AlignOf.h is a published support header that's available for use 30 // out-of-tree, and we would like that to compile cleanly at /W4. 31 #pragma warning(suppress : 4324) 32 #endif 33 T t; 34 private: 35 AlignmentCalcImpl() {} // Never instantiate. 36 }; 37 38 /// AlignOf - A templated class that contains an enum value representing 39 /// the alignment of the template argument. For example, 40 /// AlignOf<int>::Alignment represents the alignment of type "int". The 41 /// alignment calculated is the minimum alignment, and not necessarily 42 /// the "desired" alignment returned by GCC's __alignof__ (for example). Note 43 /// that because the alignment is an enum value, it can be used as a 44 /// compile-time constant (e.g., for template instantiation). 45 template <typename T> 46 struct AlignOf { 47 #ifndef _MSC_VER 48 // Avoid warnings from GCC like: 49 // comparison between 'enum llvm::AlignOf<X>::<anonymous>' and 'enum 50 // llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare] 51 // by using constexpr instead of enum. 52 // (except on MSVC, since it doesn't support constexpr yet). 53 static constexpr unsigned Alignment = 54 static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)); 55 #else 56 enum { Alignment = 57 static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) }; 58 #endif 59 enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 }; 60 enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 }; 61 enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 }; 62 enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 }; 63 64 enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 }; 65 enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 }; 66 enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 }; 67 enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 }; 68 }; 69 70 #ifndef _MSC_VER 71 template <typename T> constexpr unsigned AlignOf<T>::Alignment; 72 #endif 73 74 /// alignOf - A templated function that returns the minimum alignment of 75 /// of a type. This provides no extra functionality beyond the AlignOf 76 /// class besides some cosmetic cleanliness. Example usage: 77 /// alignOf<int>() returns the alignment of an int. 78 template <typename T> 79 inline unsigned alignOf() { return AlignOf<T>::Alignment; } 80 81 /// \struct AlignedCharArray 82 /// \brief Helper for building an aligned character array type. 83 /// 84 /// This template is used to explicitly build up a collection of aligned 85 /// character array types. We have to build these up using a macro and explicit 86 /// specialization to cope with old versions of MSVC and GCC where only an 87 /// integer literal can be used to specify an alignment constraint. Once built 88 /// up here, we can then begin to indirect between these using normal C++ 89 /// template parameters. 90 91 // MSVC requires special handling here. 92 #ifndef _MSC_VER 93 94 #if __has_feature(cxx_alignas) 95 template<std::size_t Alignment, std::size_t Size> 96 struct AlignedCharArray { 97 alignas(Alignment) char buffer[Size]; 98 }; 99 100 #elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES) 101 /// \brief Create a type with an aligned char buffer. 102 template<std::size_t Alignment, std::size_t Size> 103 struct AlignedCharArray; 104 105 #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 106 template<std::size_t Size> \ 107 struct AlignedCharArray<x, Size> { \ 108 __attribute__((aligned(x))) char buffer[Size]; \ 109 }; 110 111 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1) 112 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2) 113 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4) 114 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8) 115 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16) 116 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32) 117 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64) 118 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128) 119 120 #undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 121 122 #else 123 # error No supported align as directive. 124 #endif 125 126 #else // _MSC_VER 127 128 /// \brief Create a type with an aligned char buffer. 129 template<std::size_t Alignment, std::size_t Size> 130 struct AlignedCharArray; 131 132 // We provide special variations of this template for the most common 133 // alignments because __declspec(align(...)) doesn't actually work when it is 134 // a member of a by-value function argument in MSVC, even if the alignment 135 // request is something reasonably like 8-byte or 16-byte. Note that we can't 136 // even include the declspec with the union that forces the alignment because 137 // MSVC warns on the existence of the declspec despite the union member forcing 138 // proper alignment. 139 140 template<std::size_t Size> 141 struct AlignedCharArray<1, Size> { 142 union { 143 char aligned; 144 char buffer[Size]; 145 }; 146 }; 147 148 template<std::size_t Size> 149 struct AlignedCharArray<2, Size> { 150 union { 151 short aligned; 152 char buffer[Size]; 153 }; 154 }; 155 156 template<std::size_t Size> 157 struct AlignedCharArray<4, Size> { 158 union { 159 int aligned; 160 char buffer[Size]; 161 }; 162 }; 163 164 template<std::size_t Size> 165 struct AlignedCharArray<8, Size> { 166 union { 167 double aligned; 168 char buffer[Size]; 169 }; 170 }; 171 172 173 // The rest of these are provided with a __declspec(align(...)) and we simply 174 // can't pass them by-value as function arguments on MSVC. 175 176 #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 177 template<std::size_t Size> \ 178 struct AlignedCharArray<x, Size> { \ 179 __declspec(align(x)) char buffer[Size]; \ 180 }; 181 182 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16) 183 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32) 184 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64) 185 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128) 186 187 #undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 188 189 #endif // _MSC_VER 190 191 namespace detail { 192 template <typename T1, 193 typename T2 = char, typename T3 = char, typename T4 = char, 194 typename T5 = char, typename T6 = char, typename T7 = char, 195 typename T8 = char, typename T9 = char, typename T10 = char> 196 class AlignerImpl { 197 T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10; 198 199 AlignerImpl(); // Never defined or instantiated. 200 }; 201 202 template <typename T1, 203 typename T2 = char, typename T3 = char, typename T4 = char, 204 typename T5 = char, typename T6 = char, typename T7 = char, 205 typename T8 = char, typename T9 = char, typename T10 = char> 206 union SizerImpl { 207 char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)], 208 arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)], 209 arr9[sizeof(T9)], arr10[sizeof(T10)]; 210 }; 211 } // end namespace detail 212 213 /// \brief This union template exposes a suitably aligned and sized character 214 /// array member which can hold elements of any of up to ten types. 215 /// 216 /// These types may be arrays, structs, or any other types. The goal is to 217 /// expose a char array buffer member which can be used as suitable storage for 218 /// a placement new of any of these types. Support for more than ten types can 219 /// be added at the cost of more boilerplate. 220 template <typename T1, 221 typename T2 = char, typename T3 = char, typename T4 = char, 222 typename T5 = char, typename T6 = char, typename T7 = char, 223 typename T8 = char, typename T9 = char, typename T10 = char> 224 struct AlignedCharArrayUnion : llvm::AlignedCharArray< 225 AlignOf<detail::AlignerImpl<T1, T2, T3, T4, T5, 226 T6, T7, T8, T9, T10> >::Alignment, 227 sizeof(detail::SizerImpl<T1, T2, T3, T4, T5, 228 T6, T7, T8, T9, T10>)> { 229 }; 230 } // end namespace llvm 231 #endif 232
