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
21namespace llvm {
22template <typename T>
23struct AlignmentCalcImpl {
24  char x;
25  T t;
26private:
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).
37template <typename T>
38struct 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.
57template <typename T>
58inline 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)
74template<std::size_t Alignment, std::size_t Size>
75struct 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.
81template<std::size_t Alignment, std::size_t Size>
82struct 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
90LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1)
91LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2)
92LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4)
93LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8)
94LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
95LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
96LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
97LLVM_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.
108template<std::size_t Alignment, std::size_t Size>
109struct 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
119template<std::size_t Size>
120struct AlignedCharArray<1, Size> {
121  union {
122    char aligned;
123    char buffer[Size];
124  };
125};
126
127template<std::size_t Size>
128struct AlignedCharArray<2, Size> {
129  union {
130    short aligned;
131    char buffer[Size];
132  };
133};
134
135template<std::size_t Size>
136struct AlignedCharArray<4, Size> {
137  union {
138    int aligned;
139    char buffer[Size];
140  };
141};
142
143template<std::size_t Size>
144struct 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
161LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
162LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
163LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
164LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
165
166#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
167
168#endif // _MSC_VER
169
170namespace detail {
171template <typename T1,
172          typename T2 = char, typename T3 = char, typename T4 = char,
173          typename T5 = char, typename T6 = char, typename T7 = char,
174          typename T8 = char, typename T9 = char, typename T10 = char>
175class AlignerImpl {
176  T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
177
178  AlignerImpl(); // Never defined or instantiated.
179};
180
181template <typename T1,
182          typename T2 = char, typename T3 = char, typename T4 = char,
183          typename T5 = char, typename T6 = char, typename T7 = char,
184          typename T8 = char, typename T9 = char, typename T10 = char>
185union SizerImpl {
186  char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
187       arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
188       arr9[sizeof(T9)], arr10[sizeof(T10)];
189};
190} // end namespace detail
191
192/// \brief This union template exposes a suitably aligned and sized character
193/// array member which can hold elements of any of up to four types.
194///
195/// These types may be arrays, structs, or any other types. The goal is to
196/// expose a char array buffer member which can be used as suitable storage for
197/// a placement new of any of these types. Support for more than seven types can
198/// be added at the cost of more boiler plate.
199template <typename T1,
200          typename T2 = char, typename T3 = char, typename T4 = char,
201          typename T5 = char, typename T6 = char, typename T7 = char,
202          typename T8 = char, typename T9 = char, typename T10 = char>
203struct AlignedCharArrayUnion : llvm::AlignedCharArray<
204    AlignOf<detail::AlignerImpl<T1, T2, T3, T4, T5,
205                                T6, T7, T8, T9, T10> >::Alignment,
206    sizeof(detail::SizerImpl<T1, T2, T3, T4, T5,
207                             T6, T7, T8, T9, T10>)> {
208};
209} // end namespace llvm
210#endif
211