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// Taken from llvmCore-3425.0.31. 16 17#ifndef LLVM_SUPPORT_ALIGNOF_H 18#define LLVM_SUPPORT_ALIGNOF_H 19 20#include <cstddef> 21 22namespace objc { 23 24template <typename T> 25struct AlignmentCalcImpl { 26 char x; 27 T t; 28private: 29 AlignmentCalcImpl() {} // Never instantiate. 30}; 31 32/// AlignOf - A templated class that contains an enum value representing 33/// the alignment of the template argument. For example, 34/// AlignOf<int>::Alignment represents the alignment of type "int". The 35/// alignment calculated is the minimum alignment, and not necessarily 36/// the "desired" alignment returned by GCC's __alignof__ (for example). Note 37/// that because the alignment is an enum value, it can be used as a 38/// compile-time constant (e.g., for template instantiation). 39template <typename T> 40struct AlignOf { 41 enum { Alignment = 42 static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) }; 43 44 enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 }; 45 enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 }; 46 enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 }; 47 enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 }; 48 49 enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 }; 50 enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 }; 51 enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 }; 52 enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 }; 53 54}; 55 56/// alignOf - A templated function that returns the minimum alignment of 57/// of a type. This provides no extra functionality beyond the AlignOf 58/// class besides some cosmetic cleanliness. Example usage: 59/// alignOf<int>() returns the alignment of an int. 60template <typename T> 61inline unsigned alignOf() { return AlignOf<T>::Alignment; } 62 63 64/// \brief Helper for building an aligned character array type. 65/// 66/// This template is used to explicitly build up a collection of aligned 67/// character types. We have to build these up using a macro and explicit 68/// specialization to cope with old versions of MSVC and GCC where only an 69/// integer literal can be used to specify an alignment constraint. Once built 70/// up here, we can then begin to indirect between these using normal C++ 71/// template parameters. 72template <size_t Alignment> struct AlignedCharArrayImpl; 73 74// MSVC requires special handling here. 75#ifndef _MSC_VER 76 77#if __has_feature(cxx_alignas) 78#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 79 template <> struct AlignedCharArrayImpl<x> { \ 80 char aligned alignas(x); \ 81 } 82#elif defined(__GNUC__) 83#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 84 template <> struct AlignedCharArrayImpl<x> { \ 85 char aligned __attribute__((aligned(x))); \ 86 } 87#else 88# error No supported align as directive. 89#endif 90 91LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1); 92LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2); 93LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4); 94LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8); 95LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16); 96LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32); 97LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64); 98LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128); 99LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512); 100LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024); 101LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048); 102LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096); 103LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192); 104 105#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 106 107#else // _MSC_VER 108 109// We provide special variations of this template for the most common 110// alignments because __declspec(align(...)) doesn't actually work when it is 111// a member of a by-value function argument in MSVC, even if the alignment 112// request is something reasonably like 8-byte or 16-byte. 113template <> struct AlignedCharArrayImpl<1> { char aligned; }; 114template <> struct AlignedCharArrayImpl<2> { short aligned; }; 115template <> struct AlignedCharArrayImpl<4> { int aligned; }; 116template <> struct AlignedCharArrayImpl<8> { double aligned; }; 117 118#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \ 119 template <> struct AlignedCharArrayImpl<x> { \ 120 __declspec(align(x)) char aligned; \ 121 } 122LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16); 123LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32); 124LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64); 125LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128); 126LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512); 127LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024); 128LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048); 129LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096); 130LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192); 131// Any larger and MSVC complains. 132#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT 133 134#endif // _MSC_VER 135 136/// \brief This union template exposes a suitably aligned and sized character 137/// array member which can hold elements of any of up to four types. 138/// 139/// These types may be arrays, structs, or any other types. The goal is to 140/// produce a union type containing a character array which, when used, forms 141/// storage suitable to placement new any of these types over. Support for more 142/// than four types can be added at the cost of more boiler plate. 143template <typename T1, 144 typename T2 = char, typename T3 = char, typename T4 = char> 145union AlignedCharArrayUnion { 146private: 147 class AlignerImpl { 148 T1 t1; T2 t2; T3 t3; T4 t4; 149 150 AlignerImpl(); // Never defined or instantiated. 151 }; 152 union SizerImpl { 153 char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)]; 154 }; 155 156public: 157 /// \brief The character array buffer for use by clients. 158 /// 159 /// No other member of this union should be referenced. The exist purely to 160 /// constrain the layout of this character array. 161 char buffer[sizeof(SizerImpl)]; 162 163private: 164 // Tests seem to indicate that both Clang and GCC will properly register the 165 // alignment of a struct containing an aligned member, and this alignment 166 // should carry over to the character array in the union. 167 AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment> nonce_member; 168}; 169 170} // end namespace objc 171#endif 172