Imported Upstream version 1.66.0upstream/1.66.0

1 files changed, 69 insertions, 0 deletions

diff --git a/boost/atomic/detail/ops_gcc_ppc_common.hpp b/boost/atomic/detail/ops_gcc_ppc_common.hpp
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+/*
+ * Distributed under the Boost Software License, Version 1.0.
+ * (See accompanying file LICENSE_1_0.txt or copy at
+ * http://www.boost.org/LICENSE_1_0.txt)
+ *
+ * Copyright (c) 2009 Helge Bahmann
+ * Copyright (c) 2013 Tim Blechmann
+ * Copyright (c) 2014 Andrey Semashev
+ */
+/*!
+ * \file   atomic/detail/ops_gcc_ppc_common.hpp
+ *
+ * This header contains basic utilities for gcc PowerPC backend.
+ */
+
+#ifndef BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_
+#define BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_
+
+#include <boost/memory_order.hpp>
+#include <boost/atomic/detail/config.hpp>
+
+#ifdef BOOST_HAS_PRAGMA_ONCE
+#pragma once
+#endif
+
+namespace boost {
+namespace atomics {
+namespace detail {
+
+// The implementation below uses information from this document:
+// http://www.rdrop.com/users/paulmck/scalability/paper/N2745r.2010.02.19a.html
+
+// A note about memory_order_consume. Technically, this architecture allows to avoid
+// unnecessary memory barrier after consume load since it supports data dependency ordering.
+// However, some compiler optimizations may break a seemingly valid code relying on data
+// dependency tracking by injecting bogus branches to aid out of order execution.
+// This may happen not only in Boost.Atomic code but also in user's code, which we have no
+// control of. See this thread: http://lists.boost.org/Archives/boost/2014/06/213890.php.
+// For this reason we promote memory_order_consume to memory_order_acquire.
+
+struct gcc_ppc_operations_base
+{
+    static BOOST_CONSTEXPR_OR_CONST bool is_always_lock_free = true;
+
+    static BOOST_FORCEINLINE void fence_before(memory_order order) BOOST_NOEXCEPT
+    {
+#if defined(__powerpc64__) || defined(__PPC64__)
+        if (order == memory_order_seq_cst)
+            __asm__ __volatile__ ("sync" ::: "memory");
+        else if ((order & memory_order_release) != 0)
+            __asm__ __volatile__ ("lwsync" ::: "memory");
+#else
+        if ((order & memory_order_release) != 0)
+            __asm__ __volatile__ ("sync" ::: "memory");
+#endif
+    }
+
+    static BOOST_FORCEINLINE void fence_after(memory_order order) BOOST_NOEXCEPT
+    {
+        if ((order & (memory_order_consume | memory_order_acquire)) != 0)
+            __asm__ __volatile__ ("isync" ::: "memory");
+    }
+};
+
+} // namespace detail
+} // namespace atomics
+} // namespace boost
+
+#endif // BOOST_ATOMIC_DETAIL_OPS_GCC_PPC_COMMON_HPP_INCLUDED_