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 16template <std::size_t Indx, std::size_t Depth> 17struct C 18 : public virtual C<Indx, Depth-1>, 19 public virtual C<Indx+1, Depth-1> 20{ 21 virtual ~C() {} 22}; 23 24template <std::size_t Indx> 25struct C<Indx, 0> 26{ 27 virtual ~C() {} 28}; 29 30template <std::size_t Indx, std::size_t Depth> 31struct B 32 : public virtual C<Indx, Depth-1>, 33 public virtual C<Indx+1, Depth-1> 34{ 35}; 36 37template <class Indx, std::size_t Depth> 38struct makeB; 39 40template <std::size_t ...Indx, std::size_t Depth> 41struct makeB<std::__tuple_indices<Indx...>, Depth> 42 : public B<Indx, Depth>... 43{ 44}; 45 46template <std::size_t Width, std::size_t Depth> 47struct A 48 : public makeB<typename std::__make_tuple_indices<Width>::type, Depth> 49{ 50}; 51 52void 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 67int main() 68{ 69 test(); 70} 71 72/* 73Timing results I'm seeing (median of 3 microseconds): 74 75 libc++abi gcc's dynamic_cast 76B<Width/2, Depth> -O3 48.334 93.190 libc++abi 93% faster 77B<Width/2, Depth> -Os 58.535 94.103 libc++abi 61% faster 78A<Width, Depth> -O3 11.515 33.134 libc++abi 188% faster 79A<Width, Depth> -Os 12.631 31.553 libc++abi 150% faster 80 81*/ 82