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1 //===------------------------- dynamic_cast_stress.cpp --------------------------===//
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2 //
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3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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4 // See https://llvm.org/LICENSE.txt for license information.
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5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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6 //
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7 //===----------------------------------------------------------------------===//
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8
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9 // UNSUPPORTED: c++98, c++03
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10
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11 #include <cassert>
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12 #include <tuple>
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13 #include "support/timer.h"
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14
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15 template <std::size_t Indx, std::size_t Depth>
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16 struct C
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17 : public virtual C<Indx, Depth-1>,
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18 public virtual C<Indx+1, Depth-1>
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19 {
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20 virtual ~C() {}
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21 };
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22
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23 template <std::size_t Indx>
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24 struct C<Indx, 0>
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25 {
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26 virtual ~C() {}
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27 };
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28
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29 template <std::size_t Indx, std::size_t Depth>
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30 struct B
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31 : public virtual C<Indx, Depth-1>,
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32 public virtual C<Indx+1, Depth-1>
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33 {
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34 };
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35
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36 template <class Indx, std::size_t Depth>
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37 struct makeB;
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38
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39 template <std::size_t ...Indx, std::size_t Depth>
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40 struct makeB<std::__tuple_indices<Indx...>, Depth>
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41 : public B<Indx, Depth>...
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42 {
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43 };
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44
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45 template <std::size_t Width, std::size_t Depth>
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46 struct A
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47 : public makeB<typename std::__make_tuple_indices<Width>::type, Depth>
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48 {
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49 };
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50
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51 void test()
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52 {
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53 const std::size_t Width = 10;
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54 const std::size_t Depth = 5;
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55 A<Width, Depth> a;
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56 typedef B<Width/2, Depth> Destination;
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57 // typedef A<Width, Depth> Destination;
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58 Destination *b = nullptr;
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59 {
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60 timer t;
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61 b = dynamic_cast<Destination*>((C<Width/2, 0>*)&a);
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62 }
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63 assert(b != 0);
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64 }
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65
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66 int main()
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67 {
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68 test();
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69 }
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70
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71 /*
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72 Timing results I'm seeing (median of 3 microseconds):
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73
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74 libc++abi gcc's dynamic_cast
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75 B<Width/2, Depth> -O3 48.334 93.190 libc++abi 93% faster
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76 B<Width/2, Depth> -Os 58.535 94.103 libc++abi 61% faster
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77 A<Width, Depth> -O3 11.515 33.134 libc++abi 188% faster
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78 A<Width, Depth> -Os 12.631 31.553 libc++abi 150% faster
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79
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80 */
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