libcxx/benchmarks/libcxxabi/dynamic_cast_old_stress.bench.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-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #include <cassert>
  10 #include <cstddef>
  11 #include <utility>
  12
  13 #include "benchmark/benchmark.h"
  14
  15 template <std::size_t Indx, std::size_t Depth>
  16 struct C : public virtual C<Indx, Depth - 1>, public virtual C<Indx + 1, Depth - 1> {
  17   virtual ~C() {}
  18 };
  19
  20 template <std::size_t Indx>
  21 struct C<Indx, 0> {
  22   virtual ~C() {}
  23 };
  24
  25 template <std::size_t Indx, std::size_t Depth>
  26 struct B : public virtual C<Indx, Depth - 1>, public virtual C<Indx + 1, Depth - 1> {};
  27
  28 template <class Indx, std::size_t Depth>
  29 struct makeB;
  30
  31 template <std::size_t... Indx, std::size_t Depth>
  32 struct makeB<std::index_sequence<Indx...>, Depth> : public B<Indx, Depth>... {};
  33
  34 template <std::size_t Width, std::size_t Depth>
  35 struct A : public makeB<std::make_index_sequence<Width>, Depth> {};
  36
  37 constexpr std::size_t Width = 10;
  38 constexpr std::size_t Depth = 5;
  39
  40 template <typename Destination>
  41 void CastTo(benchmark::State& state) {
  42   A<Width, Depth> a;
  43   auto base = static_cast<C<Width / 2, 0>*>(&a);
  44
  45   Destination* b = nullptr;
  46   for (auto _ : state) {
  47     b = dynamic_cast<Destination*>(base);
  48     benchmark::DoNotOptimize(b);
  49   }
  50
  51   assert(b != 0);
  52 }
  53
  54 BENCHMARK(CastTo<B<Width / 2, Depth>>);
  55 BENCHMARK(CastTo<A<Width, Depth>>);
  56
  57 BENCHMARK_MAIN();
  58
  59 /**
  60  * Benchmark results: (release builds)
  61  *
  62  * libcxxabi:
  63  * ----------------------------------------------------------------------
  64  * Benchmark                            Time             CPU   Iterations
  65  * ----------------------------------------------------------------------
  66  * CastTo<B<Width / 2, Depth>>       1997 ns         1997 ns       349247
  67  * CastTo<A<Width, Depth>>            256 ns          256 ns      2733871
  68  *
  69  * libsupc++:
  70  * ----------------------------------------------------------------------
  71  * Benchmark                            Time             CPU   Iterations
  72  * ----------------------------------------------------------------------
  73  * CastTo<B<Width / 2, Depth>>       5240 ns         5240 ns       133091
  74  * CastTo<A<Width, Depth>>            866 ns          866 ns       808600
  75  *
  76  *
  77  */