Catch2/include/internal/benchmark/catch_optimizer.hpp

/*
 *  Created by Joachim on 16/04/2019.
 *  Adapted from donated nonius code.
 *
 *  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)
 */

 // Hinting the optimizer

#ifndef TWOBLUECUBES_CATCH_OPTIMIZER_HPP_INCLUDED
#define TWOBLUECUBES_CATCH_OPTIMIZER_HPP_INCLUDED

#if defined(_MSC_VER)
#   include <atomic> // atomic_thread_fence
#endif

namespace Catch {
    namespace Benchmark {
#if defined(__GNUC__) || defined(__clang__)
        template <typename T>
        inline void keep_memory(T* p) {
            asm volatile("" : : "g"(p) : "memory");
        }
        inline void keep_memory() {
            asm volatile("" : : : "memory");
        }

        namespace Detail {
            inline void optimizer_barrier() { keep_memory(); }
        } // namespace Detail
#elif defined(_MSC_VER)

#pragma optimize("", off)
        template <typename T>
        inline void keep_memory(T* p) {
            // thanks @milleniumbug
            *reinterpret_cast<char volatile*>(p) = *reinterpret_cast<char const volatile*>(p);
        }
        // TODO equivalent keep_memory()
#pragma optimize("", on)

        namespace Detail {
            inline void optimizer_barrier() {
                std::atomic_thread_fence(std::memory_order_seq_cst);
            }
        } // namespace Detail

#endif

        template <typename T>
        inline void deoptimize_value(T&& x) {
            keep_memory(&x);
        }

        template <typename Fn, typename... Args>
        inline auto invoke_deoptimized(Fn&& fn, Args&&... args) -> typename std::enable_if<!std::is_same<void, decltype(fn(args...))>::value>::type {
            deoptimize_value(std::forward<Fn>(fn) (std::forward<Args...>(args...)));
        }

        template <typename Fn, typename... Args>
        inline auto invoke_deoptimized(Fn&& fn, Args&&... args) -> typename std::enable_if<std::is_same<void, decltype(fn(args...))>::value>::type {
            std::forward<Fn>(fn) (std::forward<Args...>(args...));
        }
    } // namespace Benchmark
} // namespace Catch

#endif // TWOBLUECUBES_CATCH_OPTIMIZER_HPP_INCLUDED