ceph/src/boost/boost/atomic/detail/ops_gcc_ppc_common.hpp

   1 /*
   2  * Distributed under the Boost Software License, Version 1.0.
   3  * (See accompanying file LICENSE_1_0.txt or copy at
   4  * http://www.boost.org/LICENSE_1_0.txt)
   5  *
   6  * Copyright (c) 2009 Helge Bahmann
   7  * Copyright (c) 2013 Tim Blechmann
   8  * Copyright (c) 2014 Andrey Semashev
   9  */
  10 /*!
  11  * \file   atomic/detail/ops_gcc_ppc_common.hpp
  12  *
  13  * This header contains basic utilities for gcc PowerPC backend.
  14  */
  15
  16 #ifndef BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_
  17 #define BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_
  18
  19 #include <boost/memory_order.hpp>
  20 #include <boost/atomic/detail/config.hpp>
  21
  22 #ifdef BOOST_HAS_PRAGMA_ONCE
  23 #pragma once
  24 #endif
  25
  26 namespace boost {
  27 namespace atomics {
  28 namespace detail {
  29
  30 // The implementation below uses information from this document:
  31 // http://www.rdrop.com/users/paulmck/scalability/paper/N2745r.2010.02.19a.html
  32
  33 // A note about memory_order_consume. Technically, this architecture allows to avoid
  34 // unnecessary memory barrier after consume load since it supports data dependency ordering.
  35 // However, some compiler optimizations may break a seemingly valid code relying on data
  36 // dependency tracking by injecting bogus branches to aid out of order execution.
  37 // This may happen not only in Boost.Atomic code but also in user's code, which we have no
  38 // control of. See this thread: http://lists.boost.org/Archives/boost/2014/06/213890.php.
  39 // For this reason we promote memory_order_consume to memory_order_acquire.
  40
  41 struct gcc_ppc_operations_base
  42 {
  43     static BOOST_CONSTEXPR_OR_CONST bool is_always_lock_free = true;
  44
  45     static BOOST_FORCEINLINE void fence_before(memory_order order) BOOST_NOEXCEPT
  46     {
  47 #if defined(__powerpc64__) || defined(__PPC64__)
  48         if (order == memory_order_seq_cst)
  49             __asm__ __volatile__ ("sync" ::: "memory");
  50         else if ((order & memory_order_release) != 0)
  51             __asm__ __volatile__ ("lwsync" ::: "memory");
  52 #else
  53         if ((order & memory_order_release) != 0)
  54             __asm__ __volatile__ ("sync" ::: "memory");
  55 #endif
  56     }
  57
  58     static BOOST_FORCEINLINE void fence_after(memory_order order) BOOST_NOEXCEPT
  59     {
  60         if ((order & (memory_order_consume | memory_order_acquire)) != 0)
  61             __asm__ __volatile__ ("isync" ::: "memory");
  62     }
  63 };
  64
  65 } // namespace detail
  66 } // namespace atomics
  67 } // namespace boost
  68
  69 #endif // BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_