235 lines
8.1 KiB
C++
235 lines
8.1 KiB
C++
//===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the AlignOf function that computes alignments for
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// arbitrary types.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_ALIGNOF_H
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#define LLVM_SUPPORT_ALIGNOF_H
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#include <cstddef>
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#ifndef __has_feature
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# define __has_feature(x) 0
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#endif
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namespace llvm {
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template <typename T>
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struct AlignmentCalcImpl {
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char x;
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#if defined(_MSC_VER)
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// Disables "structure was padded due to __declspec(align())" warnings that are
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// generated by any class using AlignOf<T> with a manually specified alignment.
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// Although the warning is disabled in the LLVM project we need this pragma
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// as AlignOf.h is a published support header that's available for use
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// out-of-tree, and we would like that to compile cleanly at /W4.
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#pragma warning(suppress : 4324)
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#endif
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T t;
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private:
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AlignmentCalcImpl() {} // Never instantiate.
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};
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/// AlignOf - A templated class that contains an enum value representing
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/// the alignment of the template argument. For example,
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/// AlignOf<int>::Alignment represents the alignment of type "int". The
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/// alignment calculated is the minimum alignment, and not necessarily
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/// the "desired" alignment returned by GCC's __alignof__ (for example). Note
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/// that because the alignment is an enum value, it can be used as a
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/// compile-time constant (e.g., for template instantiation).
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template <typename T>
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struct AlignOf {
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#ifndef _MSC_VER
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// Avoid warnings from GCC like:
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// comparison between 'enum llvm::AlignOf<X>::<anonymous>' and 'enum
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// llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare]
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// by using constexpr instead of enum.
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// (except on MSVC, since it doesn't support constexpr yet).
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static constexpr unsigned Alignment =
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static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T));
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#else
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enum { Alignment =
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static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
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#endif
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enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
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enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
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enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 };
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enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 };
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enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 };
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enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 };
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enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 };
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enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
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};
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#ifndef _MSC_VER
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template <typename T> constexpr unsigned AlignOf<T>::Alignment;
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#endif
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/// alignOf - A templated function that returns the minimum alignment of
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/// of a type. This provides no extra functionality beyond the AlignOf
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/// class besides some cosmetic cleanliness. Example usage:
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/// alignOf<int>() returns the alignment of an int.
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template <typename T>
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inline unsigned alignOf() { return AlignOf<T>::Alignment; }
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/// \struct AlignedCharArray
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/// \brief Helper for building an aligned character array type.
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///
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/// This template is used to explicitly build up a collection of aligned
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/// character array types. We have to build these up using a macro and explicit
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/// specialization to cope with old versions of MSVC and GCC where only an
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/// integer literal can be used to specify an alignment constraint. Once built
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/// up here, we can then begin to indirect between these using normal C++
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/// template parameters.
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// MSVC requires special handling here.
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#ifndef _MSC_VER
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#if __has_feature(cxx_alignas)
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template<std::size_t Alignment, std::size_t Size>
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struct AlignedCharArray {
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alignas(Alignment) char buffer[Size];
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};
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#elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES)
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/// \brief Create a type with an aligned char buffer.
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template<std::size_t Alignment, std::size_t Size>
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struct AlignedCharArray;
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#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template<std::size_t Size> \
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struct AlignedCharArray<x, Size> { \
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__attribute__((aligned(x))) char buffer[Size]; \
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};
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
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#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
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#else
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# error No supported align as directive.
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#endif
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#else // _MSC_VER
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/// \brief Create a type with an aligned char buffer.
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template<std::size_t Alignment, std::size_t Size>
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struct AlignedCharArray;
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// We provide special variations of this template for the most common
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// alignments because __declspec(align(...)) doesn't actually work when it is
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// a member of a by-value function argument in MSVC, even if the alignment
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// request is something reasonably like 8-byte or 16-byte. Note that we can't
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// even include the declspec with the union that forces the alignment because
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// MSVC warns on the existence of the declspec despite the union member forcing
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// proper alignment.
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template<std::size_t Size>
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struct AlignedCharArray<1, Size> {
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union {
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char aligned;
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char buffer[Size];
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};
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};
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template<std::size_t Size>
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struct AlignedCharArray<2, Size> {
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union {
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short aligned;
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char buffer[Size];
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};
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};
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template<std::size_t Size>
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struct AlignedCharArray<4, Size> {
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union {
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int aligned;
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char buffer[Size];
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};
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};
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template<std::size_t Size>
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struct AlignedCharArray<8, Size> {
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union {
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double aligned;
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char buffer[Size];
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};
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};
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// The rest of these are provided with a __declspec(align(...)) and we simply
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// can't pass them by-value as function arguments on MSVC.
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#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
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template<std::size_t Size> \
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struct AlignedCharArray<x, Size> { \
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__declspec(align(x)) char buffer[Size]; \
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};
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(16)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(32)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(64)
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LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(128)
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#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
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#endif // _MSC_VER
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namespace detail {
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template <typename T1,
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typename T2 = char, typename T3 = char, typename T4 = char,
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typename T5 = char, typename T6 = char, typename T7 = char,
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typename T8 = char, typename T9 = char, typename T10 = char>
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class AlignerImpl {
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T1 t1; T2 t2; T3 t3; T4 t4; T5 t5; T6 t6; T7 t7; T8 t8; T9 t9; T10 t10;
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AlignerImpl(); // Never defined or instantiated.
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};
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template <typename T1,
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typename T2 = char, typename T3 = char, typename T4 = char,
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typename T5 = char, typename T6 = char, typename T7 = char,
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typename T8 = char, typename T9 = char, typename T10 = char>
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union SizerImpl {
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char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)],
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arr5[sizeof(T5)], arr6[sizeof(T6)], arr7[sizeof(T7)], arr8[sizeof(T8)],
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arr9[sizeof(T9)], arr10[sizeof(T10)];
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};
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} // end namespace detail
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/// \brief This union template exposes a suitably aligned and sized character
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/// array member which can hold elements of any of up to ten types.
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///
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/// These types may be arrays, structs, or any other types. The goal is to
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/// expose a char array buffer member which can be used as suitable storage for
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/// a placement new of any of these types. Support for more than ten types can
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/// be added at the cost of more boilerplate.
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template <typename T1,
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typename T2 = char, typename T3 = char, typename T4 = char,
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typename T5 = char, typename T6 = char, typename T7 = char,
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typename T8 = char, typename T9 = char, typename T10 = char>
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struct AlignedCharArrayUnion : llvm::AlignedCharArray<
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AlignOf<detail::AlignerImpl<T1, T2, T3, T4, T5,
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T6, T7, T8, T9, T10> >::Alignment,
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sizeof(detail::SizerImpl<T1, T2, T3, T4, T5,
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T6, T7, T8, T9, T10>)> {
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};
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} // end namespace llvm
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#endif
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