80 lines · cpp
1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// UNSUPPORTED: c++03, c++1110 11#include <cassert>12#include <cstddef>13#include <utility>14 15#include "benchmark/benchmark.h"16 17template <std::size_t Indx, std::size_t Depth>18struct C : public virtual C<Indx, Depth - 1>, public virtual C<Indx + 1, Depth - 1> {19 virtual ~C() {}20};21 22template <std::size_t Indx>23struct C<Indx, 0> {24 virtual ~C() {}25};26 27template <std::size_t Indx, std::size_t Depth>28struct B : public virtual C<Indx, Depth - 1>, public virtual C<Indx + 1, Depth - 1> {};29 30template <class Indx, std::size_t Depth>31struct makeB;32 33template <std::size_t... Indx, std::size_t Depth>34struct makeB<std::index_sequence<Indx...>, Depth> : public B<Indx, Depth>... {};35 36template <std::size_t Width, std::size_t Depth>37struct A : public makeB<std::make_index_sequence<Width>, Depth> {};38 39constexpr std::size_t Width = 10;40constexpr std::size_t Depth = 5;41 42template <typename Destination>43void CastTo(benchmark::State& state) {44 A<Width, Depth> a;45 auto base = static_cast<C<Width / 2, 0>*>(&a);46 47 Destination* b = nullptr;48 for (auto _ : state) {49 b = dynamic_cast<Destination*>(base);50 benchmark::DoNotOptimize(b);51 }52 53 assert(b != 0);54}55 56BENCHMARK(CastTo<B<Width / 2, Depth>>);57BENCHMARK(CastTo<A<Width, Depth>>);58 59BENCHMARK_MAIN();60 61/**62 * Benchmark results: (release builds)63 *64 * libcxxabi:65 * ----------------------------------------------------------------------66 * Benchmark Time CPU Iterations67 * ----------------------------------------------------------------------68 * CastTo<B<Width / 2, Depth>> 1997 ns 1997 ns 34924769 * CastTo<A<Width, Depth>> 256 ns 256 ns 273387170 *71 * libsupc++:72 * ----------------------------------------------------------------------73 * Benchmark Time CPU Iterations74 * ----------------------------------------------------------------------75 * CastTo<B<Width / 2, Depth>> 5240 ns 5240 ns 13309176 * CastTo<A<Width, Depth>> 866 ns 866 ns 80860077 *78 *79 */80