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
