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