fork of https://github.com/oxigraph/rocksdb and https://github.com/facebook/rocksdb for nextgraph and oxigraph
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51 lines
1.6 KiB
51 lines
1.6 KiB
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
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// This source code is licensed under both the GPLv2 (found in the
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// COPYING file in the root directory) and Apache 2.0 License
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// (found in the LICENSE.Apache file in the root directory).
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#pragma once
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#include <new>
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#include <folly/Portability.h>
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/***
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* include or backport:
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* * std::launder
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*/
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namespace folly {
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/**
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* Approximate backport from C++17 of std::launder. It should be `constexpr`
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* but that can't be done without specific support from the compiler.
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*/
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template <typename T>
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FOLLY_NODISCARD inline T* launder(T* in) noexcept {
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#if FOLLY_HAS_BUILTIN(__builtin_launder) || __GNUC__ >= 7
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// The builtin has no unwanted side-effects.
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return __builtin_launder(in);
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#elif __GNUC__
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// This inline assembler block declares that `in` is an input and an output,
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// so the compiler has to assume that it has been changed inside the block.
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__asm__("" : "+r"(in));
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return in;
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#elif defined(_WIN32)
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// MSVC does not currently have optimizations around const members of structs.
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// _ReadWriteBarrier() will prevent compiler reordering memory accesses.
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_ReadWriteBarrier();
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return in;
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#else
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static_assert(
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false, "folly::launder is not implemented for this environment");
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#endif
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}
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/* The standard explicitly forbids laundering these */
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void launder(void*) = delete;
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void launder(void const*) = delete;
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void launder(void volatile*) = delete;
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void launder(void const volatile*) = delete;
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template <typename T, typename... Args>
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void launder(T (*)(Args...)) = delete;
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} // namespace folly
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