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- //===--- AlignOf.h - Portable calculation of type alignment -----*- C++ -*-===//
- //
- // The LLVM Compiler Infrastructure
- //
- // This file is distributed under the University of Illinois Open Source
- // License. See LICENSE.TXT for details.
- //
- //===----------------------------------------------------------------------===//
- //
- // This file defines the AlignOf function that computes alignments for
- // arbitrary types.
- //
- //===----------------------------------------------------------------------===//
- #ifndef LLVM_SUPPORT_ALIGNOF_H
- #define LLVM_SUPPORT_ALIGNOF_H
- #include "Compiler.h"
- #include <cstddef>
- #include <type_traits>
- namespace llvm {
- namespace detail {
- // For everything other than an abstract class we can calulate alignment by
- // building a class with a single character and a member of the given type.
- template <typename T, bool = std::is_abstract<T>::value>
- struct AlignmentCalcImpl {
- char x;
- #if defined(_MSC_VER)
- // Disables "structure was padded due to __declspec(align())" warnings that are
- // generated by any class using AlignOf<T> with a manually specified alignment.
- // Although the warning is disabled in the LLVM project we need this pragma
- // as AlignOf.h is a published support header that's available for use
- // out-of-tree, and we would like that to compile cleanly at /W4.
- #pragma warning(suppress : 4324)
- #endif
- T t;
- private:
- AlignmentCalcImpl() = delete;
- };
- // Abstract base class helper, this will have the minimal alignment and size
- // for any abstract class. We don't even define its destructor because this
- // type should never be used in a way that requires it.
- struct AlignmentCalcImplBase {
- virtual ~AlignmentCalcImplBase() = 0;
- };
- // When we have an abstract class type, specialize the alignment computation
- // engine to create another abstract class that derives from both an empty
- // abstract base class and the provided type. This has the same effect as the
- // above except that it handles the fact that we can't actually create a member
- // of type T.
- template <typename T>
- struct AlignmentCalcImpl<T, true> : AlignmentCalcImplBase, T {
- ~AlignmentCalcImpl() override = 0;
- };
- } // End detail namespace.
- /// AlignOf - A templated class that contains an enum value representing
- /// the alignment of the template argument. For example,
- /// AlignOf<int>::Alignment represents the alignment of type "int". The
- /// alignment calculated is the minimum alignment, and not necessarily
- /// the "desired" alignment returned by GCC's __alignof__ (for example). Note
- /// that because the alignment is an enum value, it can be used as a
- /// compile-time constant (e.g., for template instantiation).
- template <typename T>
- struct AlignOf {
- #ifndef _MSC_VER
- // Avoid warnings from GCC like:
- // comparison between 'enum llvm::AlignOf<X>::<anonymous>' and 'enum
- // llvm::AlignOf<Y>::<anonymous>' [-Wenum-compare]
- // by using constexpr instead of enum.
- // (except on MSVC, since it doesn't support constexpr yet).
- static constexpr unsigned Alignment = static_cast<unsigned int>(
- sizeof(detail::AlignmentCalcImpl<T>) - sizeof(T));
- #else
- enum {
- Alignment = static_cast<unsigned int>(
- sizeof(::llvm::detail::AlignmentCalcImpl<T>) - sizeof(T))
- };
- #endif
- enum { Alignment_GreaterEqual_2Bytes = Alignment >= 2 ? 1 : 0 };
- enum { Alignment_GreaterEqual_4Bytes = Alignment >= 4 ? 1 : 0 };
- enum { Alignment_GreaterEqual_8Bytes = Alignment >= 8 ? 1 : 0 };
- enum { Alignment_GreaterEqual_16Bytes = Alignment >= 16 ? 1 : 0 };
- enum { Alignment_LessEqual_2Bytes = Alignment <= 2 ? 1 : 0 };
- enum { Alignment_LessEqual_4Bytes = Alignment <= 4 ? 1 : 0 };
- enum { Alignment_LessEqual_8Bytes = Alignment <= 8 ? 1 : 0 };
- enum { Alignment_LessEqual_16Bytes = Alignment <= 16 ? 1 : 0 };
- };
- #ifndef _MSC_VER
- template <typename T> constexpr unsigned AlignOf<T>::Alignment;
- #endif
- /// alignOf - A templated function that returns the minimum alignment of
- /// of a type. This provides no extra functionality beyond the AlignOf
- /// class besides some cosmetic cleanliness. Example usage:
- /// alignOf<int>() returns the alignment of an int.
- template <typename T>
- inline unsigned alignOf() { return AlignOf<T>::Alignment; }
- /// \struct AlignedCharArray
- /// \brief 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 old versions of MSVC and GCC 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
- #if __has_feature(cxx_alignas)
- template<std::size_t Alignment, std::size_t Size>
- struct AlignedCharArray {
- alignas(Alignment) char buffer[Size];
- };
- #elif defined(__GNUC__) || defined(__IBM_ATTRIBUTES)
- /// \brief Create a type with an aligned char buffer.
- template<std::size_t Alignment, std::size_t Size>
- struct AlignedCharArray;
- #define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
- template<std::size_t Size> \
- struct AlignedCharArray<x, Size> { \
- __attribute__((aligned(x))) char buffer[Size]; \
- };
- LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1)
- LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2)
- LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4)
- LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8)
- 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
- #else
- # error No supported align as directive.
- #endif
- #else // _MSC_VER
- /// \brief 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
- /// \brief 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> >::Alignment,
- 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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