LLVM  6.0.0svn
AlignOf.h
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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 AlignedCharArray and AlignedCharArrayUnion classes.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #ifndef LLVM_SUPPORT_ALIGNOF_H
15 #define LLVM_SUPPORT_ALIGNOF_H
16 
17 #include "llvm/Support/Compiler.h"
18 #include <cstddef>
19 
20 namespace llvm {
21 
22 /// \struct AlignedCharArray
23 /// \brief Helper for building an aligned character array type.
24 ///
25 /// This template is used to explicitly build up a collection of aligned
26 /// character array types. We have to build these up using a macro and explicit
27 /// specialization to cope with MSVC (at least till 2015) where only an
28 /// integer literal can be used to specify an alignment constraint. Once built
29 /// up here, we can then begin to indirect between these using normal C++
30 /// template parameters.
31 
32 // MSVC requires special handling here.
33 #ifndef _MSC_VER
34 
35 template<std::size_t Alignment, std::size_t Size>
37  LLVM_ALIGNAS(Alignment) char buffer[Size];
38 };
39 
40 #else // _MSC_VER
41 
42 /// \brief Create a type with an aligned char buffer.
43 template<std::size_t Alignment, std::size_t Size>
44 struct AlignedCharArray;
45 
46 // We provide special variations of this template for the most common
47 // alignments because __declspec(align(...)) doesn't actually work when it is
48 // a member of a by-value function argument in MSVC, even if the alignment
49 // request is something reasonably like 8-byte or 16-byte. Note that we can't
50 // even include the declspec with the union that forces the alignment because
51 // MSVC warns on the existence of the declspec despite the union member forcing
52 // proper alignment.
53 
54 template<std::size_t Size>
55 struct AlignedCharArray<1, Size> {
56  union {
57  char aligned;
58  char buffer[Size];
59  };
60 };
61 
62 template<std::size_t Size>
63 struct AlignedCharArray<2, Size> {
64  union {
65  short aligned;
66  char buffer[Size];
67  };
68 };
69 
70 template<std::size_t Size>
71 struct AlignedCharArray<4, Size> {
72  union {
73  int aligned;
74  char buffer[Size];
75  };
76 };
77 
78 template<std::size_t Size>
79 struct AlignedCharArray<8, Size> {
80  union {
81  double aligned;
82  char buffer[Size];
83  };
84 };
85 
86 
87 // The rest of these are provided with a __declspec(align(...)) and we simply
88 // can't pass them by-value as function arguments on MSVC.
89 
90 #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
91  template<std::size_t Size> \
92  struct AlignedCharArray<x, Size> { \
93  __declspec(align(x)) char buffer[Size]; \
94  };
95 
96 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
97 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
98 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
99 LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
100 
101 #undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
102 
103 #endif // _MSC_VER
104 
105 namespace detail {
106 template <typename T1,
107  typename T2 = char, typename T3 = char, typename T4 = char,
108  typename T5 = char, typename T6 = char, typename T7 = char,
109  typename T8 = char, typename T9 = char, typename T10 = char>
110 class AlignerImpl {
111  T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
112 
113  AlignerImpl() = delete;
114 };
115 
116 template <typename T1,
117  typename T2 = char, typename T3 = char, typename T4 = char,
118  typename T5 = char, typename T6 = char, typename T7 = char,
119  typename T8 = char, typename T9 = char, typename T10 = char>
120 union SizerImpl {
121  char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
122  arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
123  arr9[sizeof(T9)], arr10[sizeof(T10)];
124 };
125 } // end namespace detail
126 
127 /// \brief This union template exposes a suitably aligned and sized character
128 /// array member which can hold elements of any of up to ten types.
129 ///
130 /// These types may be arrays, structs, or any other types. The goal is to
131 /// expose a char array buffer member which can be used as suitable storage for
132 /// a placement new of any of these types. Support for more than ten types can
133 /// be added at the cost of more boilerplate.
134 template <typename T1,
135  typename T2 = char, typename T3 = char, typename T4 = char,
136  typename T5 = char, typename T6 = char, typename T7 = char,
137  typename T8 = char, typename T9 = char, typename T10 = char>
139  alignof(llvm::detail::AlignerImpl<T1, T2, T3, T4, T5,
140  T6, T7, T8, T9, T10>),
141  sizeof(::llvm::detail::SizerImpl<T1, T2, T3, T4, T5,
142  T6, T7, T8, T9, T10>)> {
143 };
144 } // end namespace llvm
145 
146 #endif // LLVM_SUPPORT_ALIGNOF_H
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
char buffer[Size]
Definition: AlignOf.h:37
This union template exposes a suitably aligned and sized character array member which can hold elemen...
Definition: AlignOf.h:138
#define LLVM_ALIGNAS(x)
LLVM_ALIGNAS
Definition: Compiler.h:322
constexpr char Size[]
Key for Kernel::Arg::Metadata::mSize.
Helper for building an aligned character array type.
Definition: AlignOf.h:36
#define T1