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 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 { 20 virtual ~C() {} 21 }; 22 23 template <std::size_t Indx> 24 struct C<Indx, 0> 25 { 26 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 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 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
