/*
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* Distributed under the Boost Software License, Version 1.0.
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* (See accompanying file LICENSE_1_0.txt or copy at
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* http://www.boost.org/LICENSE_1_0.txt)
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*
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* Copyright (c) 2020 Andrey Semashev
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*/
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/*!
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* \file atomic/detail/gcc_atomic_memory_order_utils.hpp
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*
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* This header contains utilities for working with gcc atomic memory order constants.
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*/
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#ifndef BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_
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#define BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_
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#include <boost/memory_order.hpp>
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#include <boost/atomic/detail/config.hpp>
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#include <boost/atomic/detail/header.hpp>
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#ifdef BOOST_HAS_PRAGMA_ONCE
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#pragma once
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#endif
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namespace boost {
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namespace atomics {
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namespace detail {
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/*!
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* The function converts \c boost::memory_order values to the compiler-specific constants.
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*
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* NOTE: The intention is that the function is optimized away by the compiler, and the
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* compiler-specific constants are passed to the intrinsics. Unfortunately, constexpr doesn't
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* work in this case because the standard atomics interface require memory ordering
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* constants to be passed as function arguments, at which point they stop being constexpr.
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* However, it is crucial that the compiler sees constants and not runtime values,
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* because otherwise it just ignores the ordering value and always uses seq_cst.
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* This is the case with Intel C++ Compiler 14.0.3 (Composer XE 2013 SP1, update 3) and
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* gcc 4.8.2. Intel Compiler issues a warning in this case:
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*
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* warning #32013: Invalid memory order specified. Defaulting to seq_cst memory order.
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*
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* while gcc acts silently.
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*
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* To mitigate the problem ALL functions, including the atomic<> members must be
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* declared with BOOST_FORCEINLINE. In this case the compilers are able to see that
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* all functions are called with constant orderings and call intrinstcts properly.
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*
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* Unfortunately, this still doesn't work in debug mode as the compiler doesn't
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* propagate constants even when functions are marked with BOOST_FORCEINLINE. In this case
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* all atomic operaions will be executed with seq_cst semantics.
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*/
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BOOST_FORCEINLINE BOOST_CONSTEXPR int convert_memory_order_to_gcc(memory_order order) BOOST_NOEXCEPT
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{
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return (order == memory_order_relaxed ? __ATOMIC_RELAXED : (order == memory_order_consume ? __ATOMIC_CONSUME :
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(order == memory_order_acquire ? __ATOMIC_ACQUIRE : (order == memory_order_release ? __ATOMIC_RELEASE :
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(order == memory_order_acq_rel ? __ATOMIC_ACQ_REL : __ATOMIC_SEQ_CST)))));
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}
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} // namespace detail
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} // namespace atomics
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} // namespace boost
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#include <boost/atomic/detail/footer.hpp>
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#endif // BOOST_ATOMIC_DETAIL_GCC_ATOMIC_MEMORY_ORDER_UTILS_HPP_INCLUDED_
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