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 #include <cassert>
11 #include <tuple>
12 #include "support/timer.hpp"
13
14 template <std::size_t Indx, std::size_t Depth>
15 struct C
16 : public virtual C<Indx, Depth-1>,
17 public virtual C<Indx+1, Depth-1>
18 {
~CC19 virtual ~C() {}
20 };
21
22 template <std::size_t Indx>
23 struct C<Indx, 0>
24 {
~CC25 virtual ~C() {}
26 };
27
28 template <std::size_t Indx, std::size_t Depth>
29 struct B
30 : public virtual C<Indx, Depth-1>,
31 public virtual C<Indx+1, Depth-1>
32 {
33 };
34
35 template <class Indx, std::size_t Depth>
36 struct makeB;
37
38 template <std::size_t ...Indx, std::size_t Depth>
39 struct makeB<std::__tuple_indices<Indx...>, Depth>
40 : public B<Indx, Depth>...
41 {
42 };
43
44 template <std::size_t Width, std::size_t Depth>
45 struct A
46 : public makeB<typename std::__make_tuple_indices<Width>::type, Depth>
47 {
48 };
49
test()50 void test()
51 {
52 const std::size_t Width = 10;
53 const std::size_t Depth = 5;
54 A<Width, Depth> a;
55 typedef B<Width/2, Depth> Destination;
56 // typedef A<Width, Depth> Destination;
57 Destination *b = nullptr;
58 {
59 timer t;
60 b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
61 }
62 assert(b != 0);
63 }
64
main()65 int main()
66 {
67 test();
68 }
69
70 /*
71 Timing results I'm seeing (median of 3 microseconds):
72
73 libc++abi gcc's dynamic_cast
74 B<Width/2, Depth> -O3 48.334 93.190 libc++abi 93% faster
75 B<Width/2, Depth> -Os 58.535 94.103 libc++abi 61% faster
76 A<Width, Depth> -O3 11.515 33.134 libc++abi 188% faster
77 A<Width, Depth> -Os 12.631 31.553 libc++abi 150% faster
78
79 */
80