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#include <type_traits> 21 22namespace llvm { 23 24namespace detail { 25 26// For everything other than an abstract class we can calulate alignment by 27// building a class with a single character and a member of the given type. 28template <typename T, bool = std::is_abstract<T>::value> 29struct AlignmentCalcImpl { 30 char x; 31#if defined(_MSC_VER) 32// Disables "structure was padded due to __declspec(align())" warnings that are 33// generated by any class using AlignOf<T> with a manually specified alignment. 34// Although the warning is disabled in the LLVM project we need this pragma 35// as AlignOf.h is a published support header that's available for use 36// out-of-tree, and we would like that to compile cleanly at /W4. 37#pragma warning(suppress : 4324) 38#endif 39 T t; 40private: 41 AlignmentCalcImpl() = delete; 42}; 43 44// Abstract base class helper, this will have the minimal alignment and size 45// for any abstract class. We don't even define its destructor because this 46// type should never be used in a way that requires it. 47struct AlignmentCalcImplBase { 48 virtual ~AlignmentCalcImplBase() = 0; 49}; 50 51// When we have an abstract class type, specialize the alignment computation 52// engine to create another abstract class that derives from both an empty 53// abstract base class and the provided type. This has the same effect as the 54// above except that it handles the fact that we can't actually create a member 55// of type T. 56template <typename T> 57struct AlignmentCalcImpl<T, true> : AlignmentCalcImplBase, T { 58 ~AlignmentCalcImpl() override = 0; 59}; 60 61} // End detail namespace. 62 63/// AlignOf - A templated class that contains an enum value representing 64/// the alignment of the template argument. For example, 65/// AlignOf<int>::Alignment represents the alignment of type "int". The 66/// alignment calculated is the minimum alignment, and not necessarily 67/// the "desired" alignment returned by GCC's __alignof__ (for example). Note 68/// that because the alignment is an enum value, it can be used as a 69/// compile-time constant (e.g., for template instantiation). 70template <typename T> 71struct AlignOf { 72#ifndef _MSC_VER 73 // Avoid warnings from GCC like: 74 // comparison between 'enum llvm::AlignOf<X>::<anonymous>' and 'enum 75 // llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare] 76 // by using constexpr instead of enum. 77 // (except on MSVC, since it doesn't support constexpr yet). 78 static constexpr unsigned Alignment = static_cast<unsigned int>( 79 sizeof(detail::AlignmentCalcImpl<T>) - sizeof(T)); 80#else 81 enum { 82 Alignment = static_cast<unsigned int>( 83 sizeof(::llvm::detail::AlignmentCalcImpl<T>) - sizeof(T)) 84 }; 85#endif 86 enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 }; 87 enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 }; 88 enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 }; 89 enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 }; 90 91 enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 }; 92 enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 }; 93 enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 }; 94 enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 }; 95}; 96 97#ifndef _MSC_VER 98template <typename T> constexpr unsigned AlignOf<T>::Alignment; 99#endif 100 101/// alignOf - A templated function that returns the minimum alignment of 102/// of a type. This provides no extra functionality beyond the AlignOf 103/// class besides some cosmetic cleanliness. Example usage: 104/// alignOf<int>() returns the alignment of an int. 105template <typename T> 106inline unsigned alignOf() { return AlignOf<T>::Alignment; } 107 108/// \struct AlignedCharArray 109/// \brief Helper for building an aligned character array type. 110/// 111/// This template is used to explicitly build up a collection of aligned 112/// character array types. We have to build these up using a macro and explicit 113/// specialization to cope with old versions of MSVC and GCC where only an 114/// integer literal can be used to specify an alignment constraint. Once built 115/// up here, we can then begin to indirect between these using normal C++ 116/// template parameters. 117 118// MSVC requires special handling here. 119#ifndef _MSC_VER 120 121#if __has_feature(cxx_alignas) 122template<std::size_t Alignment, std::size_t Size> 123struct AlignedCharArray { 124 alignas(Alignment) char buffer[Size]; 125}; 126 127#elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES) 128/// \brief Create a type with an aligned char buffer. 129template<std::size_t Alignment, std::size_t Size> 130struct AlignedCharArray; 131 132#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 133 template<std::size_t Size> \ 134 struct AlignedCharArray<x, Size> { \ 135 __attribute__((aligned(x))) char buffer[Size]; \ 136 }; 137 138LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1) 139LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2) 140LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4) 141LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8) 142LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16) 143LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32) 144LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64) 145LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128) 146 147#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 148 149#else 150# error No supported align as directive. 151#endif 152 153#else // _MSC_VER 154 155/// \brief Create a type with an aligned char buffer. 156template<std::size_t Alignment, std::size_t Size> 157struct AlignedCharArray; 158 159// We provide special variations of this template for the most common 160// alignments because __declspec(align(...)) doesn't actually work when it is 161// a member of a by-value function argument in MSVC, even if the alignment 162// request is something reasonably like 8-byte or 16-byte. Note that we can't 163// even include the declspec with the union that forces the alignment because 164// MSVC warns on the existence of the declspec despite the union member forcing 165// proper alignment. 166 167template<std::size_t Size> 168struct AlignedCharArray<1, Size> { 169 union { 170 char aligned; 171 char buffer[Size]; 172 }; 173}; 174 175template<std::size_t Size> 176struct AlignedCharArray<2, Size> { 177 union { 178 short aligned; 179 char buffer[Size]; 180 }; 181}; 182 183template<std::size_t Size> 184struct AlignedCharArray<4, Size> { 185 union { 186 int aligned; 187 char buffer[Size]; 188 }; 189}; 190 191template<std::size_t Size> 192struct AlignedCharArray<8, Size> { 193 union { 194 double aligned; 195 char buffer[Size]; 196 }; 197}; 198 199 200// The rest of these are provided with a __declspec(align(...)) and we simply 201// can't pass them by-value as function arguments on MSVC. 202 203#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 204 template<std::size_t Size> \ 205 struct AlignedCharArray<x, Size> { \ 206 __declspec(align(x)) char buffer[Size]; \ 207 }; 208 209LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16) 210LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32) 211LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64) 212LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128) 213 214#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 215 216#endif // _MSC_VER 217 218namespace detail { 219template <typename T1, 220 typename T2 = char, typename T3 = char, typename T4 = char, 221 typename T5 = char, typename T6 = char, typename T7 = char, 222 typename T8 = char, typename T9 = char, typename T10 = char> 223class AlignerImpl { 224 T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10; 225 226 AlignerImpl() = delete; 227}; 228 229template <typename T1, 230 typename T2 = char, typename T3 = char, typename T4 = char, 231 typename T5 = char, typename T6 = char, typename T7 = char, 232 typename T8 = char, typename T9 = char, typename T10 = char> 233union SizerImpl { 234 char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)], 235 arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)], 236 arr9[sizeof(T9)], arr10[sizeof(T10)]; 237}; 238} // end namespace detail 239 240/// \brief This union template exposes a suitably aligned and sized character 241/// array member which can hold elements of any of up to ten types. 242/// 243/// These types may be arrays, structs, or any other types. The goal is to 244/// expose a char array buffer member which can be used as suitable storage for 245/// a placement new of any of these types. Support for more than ten types can 246/// be added at the cost of more boilerplate. 247template <typename T1, 248 typename T2 = char, typename T3 = char, typename T4 = char, 249 typename T5 = char, typename T6 = char, typename T7 = char, 250 typename T8 = char, typename T9 = char, typename T10 = char> 251struct AlignedCharArrayUnion : llvm::AlignedCharArray< 252 AlignOf<llvm::detail::AlignerImpl<T1, T2, T3, T4, T5, 253 T6, T7, T8, T9, T10> >::Alignment, 254 sizeof(::llvm::detail::SizerImpl<T1, T2, T3, T4, T5, 255 T6, T7, T8, T9, T10>)> { 256}; 257} // end namespace llvm 258 259#endif // LLVM_SUPPORT_ALIGNOF_H 260