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 <time.h>
13 #include <stdlib.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 typedef std::chrono::high_resolution_clock Clock;
54 typedef std::chrono::duration<double, std::micro> US;
55 const std::size_t Width = 10;
56 const std::size_t Depth = 5;
57 A<Width, Depth> a;
58 typedef B<Width/2, Depth> Destination;
59 // typedef A<Width, Depth> Destination;
60 auto t0 = Clock::now();
61 Destination* b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
62 auto t1 = Clock::now();
63 std::cout << US(t1-t0).count() << " microseconds\n";
64 assert(b != 0);
65 }
66
main()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