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re PR libstdc++/87619 (sizeof(std::variant) can be reduced if its variant_size is UCHAR_MAX) 

PR libstdc++/87619

* include/std/variant (__select_index): Fix an off-by-one.
* testsuite/20_util/variant/87619.cc: New.

From-SVN: r265247
This commit is contained in:
Ville Voutilainen 2018-10-17 22:08:51 +03:00 committed by Ville Voutilainen
parent fc8abc4660
commit 4026227f21
3 changed files with 60 additions and 1 deletions
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6
libstdc++-v3/ChangeLog
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@ -1,3 +1,9 @@
2018-10-17 Ville Voutilainen <ville.voutilainen@gmail.com>
PR libstdc++/87619
* include/std/variant (__select_index): Fix an off-by-one.
* testsuite/20_util/variant/87619.cc: New.
2018-10-16 Jonathan Wakely <jwakely@redhat.com>
* include/bits/random.h (random_device) [!_GLIBCXX_USE_DEV_RANDOM]:

2
libstdc++-v3/include/std/variant
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@ -362,7 +362,7 @@ namespace __variant
template <typename... _Types>
using __select_index =
typename __select_int::_Select_int_base<sizeof...(_Types) + 1,
typename __select_int::_Select_int_base<sizeof...(_Types),
unsigned char,
unsigned short>::type::value_type;

53
libstdc++-v3/testsuite/20_util/variant/87619.cc Normal file
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@ -0,0 +1,53 @@
// Copyright (C) 2018 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
// { dg-options "-std=gnu++17" }
// { dg-do compile { target c++17 } }
#include <variant>
#include <utility>
#include <limits>
template<std::size_t I>
struct S {
};
template <std::size_t... Is>
void f_impl(std::index_sequence<Is...>)
{
using V = std::variant<S<Is>...>;
// For a variant of 255 alternatives the valid indices are [0,254]
// and index 255 means valueless-by-exception, so fits in one byte.
if constexpr (std::variant_size_v<V> <=
std::numeric_limits<unsigned char>::max())
static_assert(sizeof(V) == 2);
else
static_assert(sizeof(V) > 2);
}
template <std::size_t I>
void f()
{
f_impl(std::make_index_sequence<I>{});
}
int main()
{
f<std::numeric_limits<unsigned char>::max() - 1>();
f<std::numeric_limits<unsigned char>::max()>();
f<std::numeric_limits<unsigned char>::max() + 1>();
}