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 <chrono> 13#include <iostream> 14 15template <std::size_t Indx, std::size_t Depth> 16struct C 17 : public virtual C<Indx, Depth-1>, 18 public virtual C<Indx+1, Depth-1> 19{ 20 virtual ~C() {} 21}; 22 23template <std::size_t Indx> 24struct C<Indx, 0> 25{ 26 virtual ~C() {} 27}; 28 29template <std::size_t Indx, std::size_t Depth> 30struct B 31 : public virtual C<Indx, Depth-1>, 32 public virtual C<Indx+1, Depth-1> 33{ 34}; 35 36template <class Indx, std::size_t Depth> 37struct makeB; 38 39template <std::size_t ...Indx, std::size_t Depth> 40struct makeB<std::__tuple_indices<Indx...>, Depth> 41 : public B<Indx, Depth>... 42{ 43}; 44 45template <std::size_t Width, std::size_t Depth> 46struct A 47 : public makeB<typename std::__make_tuple_indices<Width>::type, Depth> 48{ 49}; 50 51void 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 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