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Added a workaround for gcc 4.8 not supporting alignas with a constant expression

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gcc 4.8 requires that the argument of alignas is a literal constant and does not
accept a constant expression.

This workaround is temporary, until Boost.Config updates BOOST_NO_CXX11_ALIGNAS:

https://github.com/boostorg/config/pull/324
This commit is contained in:
Andrey Semashev
2020-03-01 13:31:45 +03:00
parent f450738d7b
commit ce80ca0ce8
4 changed files with 8 additions and 3 deletions
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2
include/boost/atomic/detail/atomic_flag.hpp
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@@ -45,7 +45,7 @@ struct atomic_flag
typedef atomics::detail::operations< 1u, false > operations;
typedef operations::storage_type storage_type;
#if !defined(BOOST_NO_CXX11_ALIGNAS)
#if !defined(BOOST_ATOMIC_DETAIL_NO_CXX11_ALIGNAS)
alignas(operations::storage_alignment) storage_type m_storage;
#else
// Note: Some compilers cannot use constant expressions in alignment attributes, so we have to use the union trick

2
include/boost/atomic/detail/atomic_template.hpp
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@@ -76,7 +76,7 @@ protected:
static BOOST_CONSTEXPR_OR_CONST std::size_t storage_alignment = atomics::detail::alignment_of< value_type >::value <= operations::storage_alignment ? operations::storage_alignment : atomics::detail::alignment_of< value_type >::value;
protected:
#if !defined(BOOST_NO_CXX11_ALIGNAS)
#if !defined(BOOST_ATOMIC_DETAIL_NO_CXX11_ALIGNAS)
alignas(storage_alignment) storage_type m_storage;
#else
// Note: Some compilers cannot use constant expressions in alignment attributes, so we have to use the union trick

5
include/boost/atomic/detail/config.hpp
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@@ -54,6 +54,11 @@
#endif
#endif // defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
#if defined(BOOST_NO_CXX11_ALIGNAS) || (defined(BOOST_GCC) && (BOOST_GCC+0) < 40900)
// This macro indicates that the compiler doesn't support alignas with a constant expression as an argument
#define BOOST_ATOMIC_DETAIL_NO_CXX11_ALIGNAS
#endif
// Enable pointer/reference casts between storage and value when possible.
// Note: Despite that MSVC does not employ strict aliasing rules for optimizations
// and does not require an explicit markup for types that may alias, we still don't

2
include/boost/atomic/detail/storage_traits.hpp
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@@ -42,7 +42,7 @@ BOOST_FORCEINLINE void non_atomic_load(T const volatile& from, T& to) BOOST_NOEX
template< std::size_t Size, std::size_t Alignment = 1u >
struct BOOST_ATOMIC_DETAIL_MAY_ALIAS buffer_storage
{
#if !defined(BOOST_NO_CXX11_ALIGNAS)
#if !defined(BOOST_ATOMIC_DETAIL_NO_CXX11_ALIGNAS)
alignas(Alignment) unsigned char data[Size];
#else
union