mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-12-14 18:51:28 +00:00
319d3205ce
Currently, MOZ_ALIGNED_DECL uses the order (_type, _align) for its parameters. However, this order makes the code less readable when _type is a larger object like a struct because the value for _align would be at the end of the struct definition. By swapping the order of _type and _align, the alignment value will always be next to the type name, regardless how far the definition of _type extends. Differential Revision: https://phabricator.services.mozilla.com/D77288
139 lines
3.6 KiB
C++
139 lines
3.6 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this
|
|
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
/* Functionality related to memory alignment. */
|
|
|
|
#ifndef mozilla_Alignment_h
|
|
#define mozilla_Alignment_h
|
|
|
|
#include "mozilla/Attributes.h"
|
|
#include <stddef.h>
|
|
#include <stdint.h>
|
|
|
|
namespace mozilla {
|
|
|
|
/*
|
|
* This class, and the corresponding macro MOZ_ALIGNOF, figures out how many
|
|
* bytes of alignment a given type needs.
|
|
*/
|
|
template <typename T>
|
|
class AlignmentFinder {
|
|
struct Aligner {
|
|
char mChar;
|
|
T mT;
|
|
|
|
// Aligner may be used to check alignment of types with deleted dtors. This
|
|
// results in such specializations having implicitly deleted dtors, which
|
|
// causes fatal warnings on MSVC (see bug 1481005). As we don't create
|
|
// Aligners, we can avoid this warning by explicitly deleting the dtor.
|
|
~Aligner() = delete;
|
|
};
|
|
|
|
public:
|
|
static const size_t alignment = sizeof(Aligner) - sizeof(T);
|
|
};
|
|
|
|
#define MOZ_ALIGNOF(T) mozilla::AlignmentFinder<T>::alignment
|
|
|
|
namespace detail {
|
|
template <typename T>
|
|
struct AlignasHelper {
|
|
T mT;
|
|
};
|
|
} // namespace detail
|
|
|
|
/*
|
|
* Use this instead of alignof to align struct field as if it is inside
|
|
* a struct. On some platforms, there exist types which have different
|
|
* alignment between when it is used on its own and when it is used on
|
|
* a struct field.
|
|
*
|
|
* Known examples are 64bit types (uint64_t, double) on 32bit Linux,
|
|
* where they have 8byte alignment on their own, and 4byte alignment
|
|
* when in struct.
|
|
*/
|
|
#define MOZ_ALIGNAS_IN_STRUCT(T) alignas(mozilla::detail::AlignasHelper<T>)
|
|
|
|
/*
|
|
* Declare the MOZ_ALIGNED_DECL macro for declaring aligned types.
|
|
*
|
|
* For instance,
|
|
*
|
|
* MOZ_ALIGNED_DECL(8, char arr[2]);
|
|
*
|
|
* will declare a two-character array |arr| aligned to 8 bytes.
|
|
*/
|
|
|
|
#if defined(__GNUC__)
|
|
# define MOZ_ALIGNED_DECL(_align, _type) _type __attribute__((aligned(_align)))
|
|
#elif defined(_MSC_VER)
|
|
# define MOZ_ALIGNED_DECL(_align, _type) __declspec(align(_align)) _type
|
|
#else
|
|
# warning "We don't know how to align variables on this compiler."
|
|
# define MOZ_ALIGNED_DECL(_align, _type) _type
|
|
#endif
|
|
|
|
/*
|
|
* AlignedElem<N> is a structure whose alignment is guaranteed to be at least N
|
|
* bytes.
|
|
*
|
|
* We support 1, 2, 4, 8, and 16-byte alignment.
|
|
*/
|
|
template <size_t Align>
|
|
struct AlignedElem;
|
|
|
|
/*
|
|
* We have to specialize this template because GCC doesn't like
|
|
* __attribute__((aligned(foo))) where foo is a template parameter.
|
|
*/
|
|
|
|
template <>
|
|
struct AlignedElem<1> {
|
|
MOZ_ALIGNED_DECL(1, uint8_t elem);
|
|
};
|
|
|
|
template <>
|
|
struct AlignedElem<2> {
|
|
MOZ_ALIGNED_DECL(2, uint8_t elem);
|
|
};
|
|
|
|
template <>
|
|
struct AlignedElem<4> {
|
|
MOZ_ALIGNED_DECL(4, uint8_t elem);
|
|
};
|
|
|
|
template <>
|
|
struct AlignedElem<8> {
|
|
MOZ_ALIGNED_DECL(8, uint8_t elem);
|
|
};
|
|
|
|
template <>
|
|
struct AlignedElem<16> {
|
|
MOZ_ALIGNED_DECL(16, uint8_t elem);
|
|
};
|
|
|
|
template <typename T>
|
|
struct MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS AlignedStorage2 {
|
|
union U {
|
|
char mBytes[sizeof(T)];
|
|
uint64_t mDummy;
|
|
} u;
|
|
|
|
const T* addr() const { return reinterpret_cast<const T*>(u.mBytes); }
|
|
T* addr() { return static_cast<T*>(static_cast<void*>(u.mBytes)); }
|
|
|
|
AlignedStorage2() = default;
|
|
|
|
// AlignedStorage2 is non-copyable: the default copy constructor violates
|
|
// strict aliasing rules, per bug 1269319.
|
|
AlignedStorage2(const AlignedStorage2&) = delete;
|
|
void operator=(const AlignedStorage2&) = delete;
|
|
};
|
|
|
|
} /* namespace mozilla */
|
|
|
|
#endif /* mozilla_Alignment_h */
|