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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 40 : 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
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