48 lines
1.5 KiB
C++
48 lines
1.5 KiB
C++
/*
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* Copyright (c) Meta Platforms, Inc. and 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 <folly/Portability.h>
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#include <folly/lang/Hint.h>
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namespace folly {
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/**
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* Call doNotOptimizeAway(var) to ensure that var will be computed even
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* post-optimization. Use it for variables that are computed during
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* benchmarking but otherwise are useless. The compiler tends to do a
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* good job at eliminating unused variables, and this function fools it
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* into thinking var is in fact needed.
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*
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* Call makeUnpredictable(var) when you don't want the optimizer to use
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* its knowledge of var to shape the following code. This is useful
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* when constant propagation or power reduction is possible during your
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* benchmark but not in real use cases.
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*/
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template <class T>
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FOLLY_ALWAYS_INLINE void doNotOptimizeAway(const T& datum) {
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compiler_must_not_elide(datum);
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}
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template <typename T>
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FOLLY_ALWAYS_INLINE void makeUnpredictable(T& datum) {
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compiler_must_not_predict(datum);
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}
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} // namespace folly
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