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