libcxxabi/test/dynamic_cast_stress.pass.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 // UNSUPPORTED: c++03
  10
  11 #include <cassert>
  12 #include <tuple>
  13 #include "support/timer.h"
  14
  15 template <std::size_t Indx, std::size_t Depth>
  16 struct C
  17     : public virtual C<Indx, Depth-1>,
  18       public virtual C<Indx+1, Depth-1>
  19 {
  20     virtual ~C() {}
  21 };
  22
  23 template <std::size_t Indx>
  24 struct C<Indx, 0>
  25 {
  26     virtual ~C() {}
  27 };
  28
  29 template <std::size_t Indx, std::size_t Depth>
  30 struct B
  31     : public virtual C<Indx, Depth-1>,
  32       public virtual C<Indx+1, Depth-1>
  33 {
  34 };
  35
  36 template <class Indx, std::size_t Depth>
  37 struct makeB;
  38
  39 template <std::size_t ...Indx, std::size_t Depth>
  40 struct makeB<std::__tuple_indices<Indx...>, Depth>
  41     : public B<Indx, Depth>...
  42 {
  43 };
  44
  45 template <std::size_t Width, std::size_t Depth>
  46 struct A
  47     : public makeB<typename std::__make_tuple_indices<Width>::type, Depth>
  48 {
  49 };
  50
  51 void test()
  52 {
  53     const std::size_t Width = 10;
  54     const std::size_t Depth = 5;
  55     A<Width, Depth> a;
  56     typedef B<Width/2, Depth> Destination;
  57 //    typedef A<Width, Depth> Destination;
  58     Destination *b = nullptr;
  59     {
  60         timer t;
  61         b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
  62     }
  63     assert(b != 0);
  64 }
  65
  66 int main(int, char**)
  67 {
  68     test();
  69
  70     return 0;
  71 }
  72
  73 /*
  74 Timing results I'm seeing (median of 3 microseconds):
  75
  76                           libc++abi    gcc's dynamic_cast
  77 B<Width/2, Depth> -O3      48.334         93.190           libc++abi 93% faster
  78 B<Width/2, Depth> -Os      58.535         94.103           libc++abi 61% faster
  79 A<Width, Depth>   -O3      11.515         33.134           libc++abi 188% faster
  80 A<Width, Depth>   -Os      12.631         31.553           libc++abi 150% faster
  81
  82 */