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//===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the AlignedCharArray and AlignedCharArrayUnion classes.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_ALIGNOF_H
#define LLVM_SUPPORT_ALIGNOF_H
#include "llvm/Support/Compiler.h"
#include <cstddef>
namespace llvm {
/// \struct AlignedCharArray
/// Helper for building an aligned character array type.
///
/// This template is used to explicitly build up a collection of aligned
/// character array types. We have to build these up using a macro and explicit
/// specialization to cope with MSVC (at least till 2015) where only an
/// integer literal can be used to specify an alignment constraint. Once built
/// up here, we can then begin to indirect between these using normal C++
/// template parameters.
// MSVC requires special handling here.
#ifndef _MSC_VER
template<std::size_t Alignment, std::size_t Size>
struct AlignedCharArray {
alignas(Alignment) char buffer[Size];
};
#else // _MSC_VER
/// Create a type with an aligned char buffer.
template<std::size_t Alignment, std::size_t Size>
struct AlignedCharArray;
// We provide special variations of this template for the most common
// alignments because __declspec(align(...)) doesn't actually work when it is
// a member of a by-value function argument in MSVC, even if the alignment
// request is something reasonably like 8-byte or 16-byte. Note that we can't
// even include the declspec with the union that forces the alignment because
// MSVC warns on the existence of the declspec despite the union member forcing
// proper alignment.
template<std::size_t Size>
struct AlignedCharArray<1, Size> {
union {
char aligned;
char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<2, Size> {
union {
short aligned;
char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<4, Size> {
union {
int aligned;
char buffer[Size];
};
};
template<std::size_t Size>
struct AlignedCharArray<8, Size> {
union {
double aligned;
char buffer[Size];
};
};
// The rest of these are provided with a __declspec(align(...)) and we simply
// can't pass them by-value as function arguments on MSVC.
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template<std::size_t Size> \
struct AlignedCharArray<x, Size> { \
__declspec(align(x)) char buffer[Size]; \
};
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
#endif // _MSC_VER
namespace detail {
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char,
typename T5 = char, typename T6 = char, typename T7 = char,
typename T8 = char, typename T9 = char, typename T10 = char>
class AlignerImpl {
T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
AlignerImpl() = delete;
};
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char,
typename T5 = char, typename T6 = char, typename T7 = char,
typename T8 = char, typename T9 = char, typename T10 = char>
union SizerImpl {
char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
arr9[sizeof(T9)], arr10[sizeof(T10)];
};
} // end namespace detail
/// This union template exposes a suitably aligned and sized character
/// array member which can hold elements of any of up to ten types.
///
/// These types may be arrays, structs, or any other types. The goal is to
/// expose a char array buffer member which can be used as suitable storage for
/// a placement new of any of these types. Support for more than ten types can
/// be added at the cost of more boilerplate.
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char,
typename T5 = char, typename T6 = char, typename T7 = char,
typename T8 = char, typename T9 = char, typename T10 = char>
struct AlignedCharArrayUnion : llvm::AlignedCharArray<
alignof(llvm::detail::AlignerImpl<T1, T2, T3, T4, T5,
T6, T7, T8, T9, T10>),
sizeof(::llvm::detail::SizerImpl<T1, T2, T3, T4, T5,
T6, T7, T8, T9, T10>)> {
};
} // end namespace llvm
#endif // LLVM_SUPPORT_ALIGNOF_H
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