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 {
~CC20 virtual ~C() {}
21 };
22
23 template <std::size_t Indx>
24 struct C<Indx, 0>
25 {
~CC26 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
test()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
main(int,char **)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 */
83