74 lines
1.8 KiB
C++
74 lines
1.8 KiB
C++
/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <cstdlib>
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#include <folly/Portability.h>
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namespace folly {
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namespace detail {
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extern void assume_check(bool cond);
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} // namespace detail
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/**
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* Inform the compiler that the argument can be assumed true. It is
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* undefined behavior if the argument is not actually true, so use
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* with care.
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*
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* Implemented as a function instead of a macro because
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* __builtin_assume does not evaluate its argument at runtime, so it
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* cannot be used with expressions that have side-effects.
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*/
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FOLLY_ALWAYS_INLINE void assume(bool cond) {
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if (kIsDebug) {
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detail::assume_check(cond);
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} else {
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#if defined(__clang__) // Must go first because Clang also defines __GNUC__.
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__builtin_assume(cond);
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#elif defined(__GNUC__)
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if (!cond) {
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__builtin_unreachable();
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}
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#elif defined(_MSC_VER)
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__assume(cond);
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#else
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// Do nothing.
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#endif
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}
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}
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[[noreturn]] FOLLY_ALWAYS_INLINE void assume_unreachable() {
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assume(false);
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// Do a bit more to get the compiler to understand
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// that this function really will never return.
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#if defined(__GNUC__)
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__builtin_unreachable();
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#elif defined(_MSC_VER)
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__assume(0);
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#else
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// Well, it's better than nothing.
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std::abort();
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#endif
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}
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} // namespace folly
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