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1 // RUN: %clang_cc1 -std=c++17 %s -verify
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2 // expected-no-diagnostics
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3
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4 // This test attempts to ensure that the below template parameter pack
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5 // splitting technique executes in linear time in the number of template
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6 // parameters. The size of the list below is selected so as to execute
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7 // relatively quickly on a "good" compiler and to time out otherwise.
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8
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9 template<typename...> struct TypeList;
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10
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11 namespace detail {
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12 template<unsigned> using Unsigned = unsigned;
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13 template<typename T, T ...N> using ListOfNUnsignedsImpl = TypeList<Unsigned<N>...>;
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14 template<unsigned N> using ListOfNUnsigneds =
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15 __make_integer_seq<ListOfNUnsignedsImpl, unsigned, N>;
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16
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17 template<typename T> struct TypeWrapper {
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18 template<unsigned> using AsTemplate = T;
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19 };
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20
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21 template<typename ...N> struct Splitter {
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22 template<template<N> class ...L,
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23 template<unsigned> class ...R> struct Split {
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24 using Left = TypeList<L<0>...>;
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25 using Right = TypeList<R<0>...>;
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26 };
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27 };
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28 }
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29
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30 template<typename TypeList, unsigned N, typename = detail::ListOfNUnsigneds<N>>
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31 struct SplitAtIndex;
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32
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33 template<typename ...T, unsigned N, typename ...NUnsigneds>
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34 struct SplitAtIndex<TypeList<T...>, N, TypeList<NUnsigneds...>> :
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35 detail::Splitter<NUnsigneds...>::
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36 template Split<detail::TypeWrapper<T>::template AsTemplate...> {};
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37
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38 template<typename T, int N> struct Rep : Rep<typename Rep<T, N-1>::type, 1> {};
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39 template<typename ...T> struct Rep<TypeList<T...>, 1> { typedef TypeList<T..., T...> type; };
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40
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41 using Ints = Rep<TypeList<int>, 14>::type;
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42
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43 template<typename T> extern int Size;
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44 template<typename ...T> constexpr int Size<TypeList<T...>> = sizeof...(T);
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45
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46 using Left = SplitAtIndex<Ints, Size<Ints> / 2>::Left;
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47 using Right = SplitAtIndex<Ints, Size<Ints> / 2>::Right;
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48 static_assert(Size<Left> == 8192);
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49 static_assert(Size<Right> == 8192);
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50
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51 template<typename L, typename R> struct Concat;
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52 template<typename ...L, typename ...R> struct Concat<TypeList<L...>, TypeList<R...>> {
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53 using type = TypeList<L..., R...>;
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54 };
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55
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56 using Ints = Concat<Left, Right>::type;
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