temp-param-subst-linear.cpp
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// RUN: %clang_cc1 -std=c++17 %s -verify
// expected-no-diagnostics
// This test attempts to ensure that the below template parameter pack
// splitting technique executes in linear time in the number of template
// parameters. The size of the list below is selected so as to execute
// relatively quickly on a "good" compiler and to time out otherwise.
template<typename...> struct TypeList;
namespace detail {
template<unsigned> using Unsigned = unsigned;
template<typename T, T ...N> using ListOfNUnsignedsImpl = TypeList<Unsigned<N>...>;
template<unsigned N> using ListOfNUnsigneds =
__make_integer_seq<ListOfNUnsignedsImpl, unsigned, N>;
template<typename T> struct TypeWrapper {
template<unsigned> using AsTemplate = T;
};
template<typename ...N> struct Splitter {
template<template<N> class ...L,
template<unsigned> class ...R> struct Split {
using Left = TypeList<L<0>...>;
using Right = TypeList<R<0>...>;
};
};
}
template<typename TypeList, unsigned N, typename = detail::ListOfNUnsigneds<N>>
struct SplitAtIndex;
template<typename ...T, unsigned N, typename ...NUnsigneds>
struct SplitAtIndex<TypeList<T...>, N, TypeList<NUnsigneds...>> :
detail::Splitter<NUnsigneds...>::
template Split<detail::TypeWrapper<T>::template AsTemplate...> {};
template<typename T, int N> struct Rep : Rep<typename Rep<T, N-1>::type, 1> {};
template<typename ...T> struct Rep<TypeList<T...>, 1> { typedef TypeList<T..., T...> type; };
using Ints = Rep<TypeList<int>, 14>::type;
template<typename T> extern int Size;
template<typename ...T> constexpr int Size<TypeList<T...>> = sizeof...(T);
using Left = SplitAtIndex<Ints, Size<Ints> / 2>::Left;
using Right = SplitAtIndex<Ints, Size<Ints> / 2>::Right;
static_assert(Size<Left> == 8192);
static_assert(Size<Right> == 8192);
template<typename L, typename R> struct Concat;
template<typename ...L, typename ...R> struct Concat<TypeList<L...>, TypeList<R...>> {
using type = TypeList<L..., R...>;
};
using Ints = Concat<Left, Right>::type;