1 //===------------------------- dynamic_cast_stress.cpp --------------------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is dual licensed under the MIT and the University of Illinois Open
6 // Source Licenses. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 // UNSUPPORTED: c++98, c++03
11 
12 #include <cassert>
13 #include <tuple>
14 #include "support/timer.hpp"
15 
16 template <std::size_t Indx, std::size_t Depth>
17 struct C
18     : public virtual C<Indx, Depth-1>,
19       public virtual C<Indx+1, Depth-1>
20 {
21     virtual ~C() {}
22 };
23 
24 template <std::size_t Indx>
25 struct C<Indx, 0>
26 {
27     virtual ~C() {}
28 };
29 
30 template <std::size_t Indx, std::size_t Depth>
31 struct B
32     : public virtual C<Indx, Depth-1>,
33       public virtual C<Indx+1, Depth-1>
34 {
35 };
36 
37 template <class Indx, std::size_t Depth>
38 struct makeB;
39 
40 template <std::size_t ...Indx, std::size_t Depth>
41 struct makeB<std::__tuple_indices<Indx...>, Depth>
42     : public B<Indx, Depth>...
43 {
44 };
45 
46 template <std::size_t Width, std::size_t Depth>
47 struct A
48     : public makeB<typename std::__make_tuple_indices<Width>::type, Depth>
49 {
50 };
51 
52 void test()
53 {
54     const std::size_t Width = 10;
55     const std::size_t Depth = 5;
56     A<Width, Depth> a;
57     typedef B<Width/2, Depth> Destination;
58 //    typedef A<Width, Depth> Destination;
59     Destination *b = nullptr;
60     {
61         timer t;
62         b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
63     }
64     assert(b != 0);
65 }
66 
67 int main()
68 {
69     test();
70 }
71 
72 /*
73 Timing results I'm seeing (median of 3 microseconds):
74 
75                           libc++abi    gcc's dynamic_cast
76 B<Width/2, Depth> -O3      48.334         93.190           libc++abi 93% faster
77 B<Width/2, Depth> -Os      58.535         94.103           libc++abi 61% faster
78 A<Width, Depth>   -O3      11.515         33.134           libc++abi 188% faster
79 A<Width, Depth>   -Os      12.631         31.553           libc++abi 150% faster
80 
81 */
82