Utility.hpp

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// The Reactive C++ Toolbox.
// Copyright (C) 2021 Reactive Markets Limited
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
 
#ifndef TOOLBOX_BM_UTILITY_HPP
#define TOOLBOX_BM_UTILITY_HPP
 
namespace toolbox::bm {
 
// The clobber_memory and do_not_optimise functions below are used to defeat the optimiser.
// See CppCon 2015: Chandler Carruth "Tuning C++: Benchmarks, and CPUs, and Compilers! Oh My!"
// And https://github.com/google/benchmark/blob/master/include/benchmark/benchmark.h
 
inline void clobber_memory() noexcept
{
    asm volatile("" ::: "memory");
}
 
template <typename ValueT>
inline void do_not_optimise(const ValueT& val) noexcept
{
    asm volatile("" : : "r,m"(val) : "memory");
}
 
template <typename ValueT>
inline void do_not_optimise(ValueT& val) noexcept
{
#if defined(__clang__)
    asm volatile("" : "+r,m"(val) : : "memory");
#else
    asm volatile("" : "+m,r"(val) : : "memory");
#endif
}
} // namespace toolbox::bm
 
#endif // TOOLBOX_BM_UTILITY_HPP