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From: "dartdart26 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/101923] std::function's move ctor is slower than the
 copy one for empty source objects
Date: Sun, 15 Aug 2021 13:38:32 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101923

--- Comment #1 from Petar Ivanov <dartdart26 at gmail dot com> ---
Benchmark code (using Google Benchmark):

#include <benchmark/benchmark.h>

#include <functional>
#include <utility>

struct Car {};

static void copy(benchmark::State& state) {
  for (auto _ : state) {
    const auto f =3D std::function<void(const Car&)>{};
    const auto copied =3D f;
    benchmark::DoNotOptimize(copied);
  }
}

static void move(benchmark::State& state) {
  for (auto _ : state) {
    auto f =3D std::function<void(const Car&)>{};
    const auto moved =3D std::move(f);
    benchmark::DoNotOptimize(moved);
  }
}

BENCHMARK(copy);
BENCHMARK(move);

BENCHMARK_MAIN();=