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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 "llvm/Support/Compiler.h"
#include <cstddef>
namespace llvm {
template <typename T>
struct AlignmentCalcImpl {
char x;
T t;
private:
AlignmentCalcImpl() {} // Never instantiate.
};
/// 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 {
enum { Alignment =
static_cast<unsigned int>(sizeof(AlignmentCalcImpl<T>) - sizeof(T)) };
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 };
};
/// 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>
static inline unsigned alignOf() { return AlignOf<T>::Alignment; }
/// \brief Helper for building an aligned character array type.
///
/// This template is used to explicitly build up a collection of aligned
/// character 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.
template <size_t Alignment> struct AlignedCharArrayImpl {};
template <> struct AlignedCharArrayImpl<0> {
typedef char type;
};
#if __cplusplus == 201103L || __has_feature(cxx_alignas)
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
typedef char alignas(x) type; \
}
#elif defined(__clang__) || defined(__GNUC__)
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
typedef char type __attribute__((aligned(x))); \
}
#elif defined(_MSC_VER)
#define LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(x) \
template <> struct AlignedCharArrayImpl<x> { \
typedef __declspec(align(x)) char type; \
}
#else
# error No supported align as directive.
#endif
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);
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(512);
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(1024);
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(2048);
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(4096);
LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT(8192);
// Any larger and MSVC complains.
#undef LLVM_ALIGNEDCHARARRAY_TEMPLATE_ALIGNMENT
/// \brief This class template exposes a typedef for type containing a suitable
/// aligned character array to hold elements of any of up to four types.
///
/// These types may be arrays, structs, or any other types. The goal is to
/// produce a union type containing a character array which, when used, forms
/// storage suitable to placement new any of these types over. Support for more
/// than four types can be added at the cost of more boiler plate.
template <typename T1,
typename T2 = char, typename T3 = char, typename T4 = char>
class AlignedCharArray {
class AlignerImpl {
T1 t1; T2 t2; T3 t3; T4 t4;
AlignerImpl(); // Never defined or instantiated.
};
union SizerImpl {
char arr1[sizeof(T1)], arr2[sizeof(T2)], arr3[sizeof(T3)], arr4[sizeof(T4)];
};
public:
// Sadly, Clang and GCC both fail to align a character array properly even
// with an explicit alignment attribute. To work around this, we union
// the character array that will actually be used with a struct that contains
// a single aligned character member. Tests seem to indicate that both Clang
// and GCC will properly register the alignment of a struct containing an
// aligned member, and this alignment should carry over to the character
// array in the union.
union union_type {
// This is the only member of the union which should be used by clients:
char buffer[sizeof(SizerImpl)];
// This member of the union only exists to force the alignment.
struct {
typename llvm::AlignedCharArrayImpl<AlignOf<AlignerImpl>::Alignment>::type
nonce_inner_member;
} nonce_member;
};
};
} // end namespace llvm
#endif
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