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* [gcc(refs/vendors/redhat/heads/gcc-8-branch)] libstdc++: Fix is_trivially_constructible (PR 94033)
@ 2020-09-17 17:18 Jakub Jelinek
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From: Jakub Jelinek @ 2020-09-17 17:18 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:ccfe790fda66df542c08ce1f1cbc287d9a487755
commit ccfe790fda66df542c08ce1f1cbc287d9a487755
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Mar 18 23:19:12 2020 +0000
libstdc++: Fix is_trivially_constructible (PR 94033)
This attempts to make is_nothrow_constructible more robust (and
efficient to compile) by not depending on is_constructible. Instead the
__is_constructible intrinsic is used directly. The helper class
__is_nt_constructible_impl which checks whether the construction is
non-throwing now takes a bool template parameter that is substituted by
the result of the instrinsic. This fixes the reported bug by not using
the already-instantiated (and incorrect) value of std::is_constructible.
I don't think it really fixes the problem in general, because
std::is_nothrow_constructible itself could already have been
instantiated in a context where it gives the wrong result. A proper fix
needs to be done in the compiler.
Backported to the gcc-8 and gcc-9 branches to fix PR 96999.
PR libstdc++/94033
* include/std/type_traits (__is_nt_default_constructible_atom): Remove.
(__is_nt_default_constructible_impl): Remove.
(__is_nothrow_default_constructible_impl): Remove.
(__is_nt_constructible_impl): Add bool template parameter. Adjust
partial specializations.
(__is_nothrow_constructible_impl): Replace class template with alias
template.
(is_nothrow_default_constructible): Derive from alias template
__is_nothrow_constructible_impl instead of
__is_nothrow_default_constructible_impl.
* testsuite/20_util/is_nothrow_constructible/94003.cc: New test.
(cherry picked from commit b3341826531e80e02f194460b4fbe1b0541c0463)
Diff:
---
libstdc++-v3/include/std/type_traits | 57 ++++++++++------------
.../20_util/is_nothrow_constructible/94003.cc | 46 +++++++++++++++++
.../is_nothrow_default_constructible/96999.cc | 54 ++++++++++++++++++++
3 files changed, 125 insertions(+), 32 deletions(-)
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index e0394179963..6c32dd4a51f 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -915,55 +915,48 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: public __is_move_constructible_impl<_Tp>
{ };
- template<typename _Tp>
- struct __is_nt_default_constructible_atom
- : public integral_constant<bool, noexcept(_Tp())>
+ template<bool, typename _Tp, typename... _Args>
+ struct __is_nt_constructible_impl
+ : public false_type
{ };
- template<typename _Tp, bool = is_array<_Tp>::value>
- struct __is_nt_default_constructible_impl;
+ template<typename _Tp, typename... _Args>
+ struct __is_nt_constructible_impl<true, _Tp, _Args...>
+ : public __bool_constant<noexcept(_Tp(std::declval<_Args>()...))>
+ { };
- template<typename _Tp>
- struct __is_nt_default_constructible_impl<_Tp, true>
- : public __and_<__is_array_known_bounds<_Tp>,
- __is_nt_default_constructible_atom<typename
- remove_all_extents<_Tp>::type>>
+ template<typename _Tp, typename _Arg>
+ struct __is_nt_constructible_impl<true, _Tp, _Arg>
+ : public __bool_constant<noexcept(static_cast<_Tp>(std::declval<_Arg>()))>
{ };
template<typename _Tp>
- struct __is_nt_default_constructible_impl<_Tp, false>
- : public __is_nt_default_constructible_atom<_Tp>
+ struct __is_nt_constructible_impl<true, _Tp>
+ : public __bool_constant<noexcept(_Tp())>
{ };
- /// is_nothrow_default_constructible
- template<typename _Tp>
- struct is_nothrow_default_constructible
- : public __and_<is_default_constructible<_Tp>,
- __is_nt_default_constructible_impl<_Tp>>
+ template<typename _Tp, size_t _Num>
+ struct __is_nt_constructible_impl<true, _Tp[_Num]>
+ : public __bool_constant<noexcept(typename remove_all_extents<_Tp>::type())>
{ };
template<typename _Tp, typename... _Args>
- struct __is_nt_constructible_impl
- : public integral_constant<bool, noexcept(_Tp(declval<_Args>()...))>
- { };
+ using __is_nothrow_constructible_impl
+ = __is_nt_constructible_impl<__is_constructible(_Tp, _Args...),
+ _Tp, _Args...>;
- template<typename _Tp, typename _Arg>
- struct __is_nt_constructible_impl<_Tp, _Arg>
- : public integral_constant<bool,
- noexcept(static_cast<_Tp>(declval<_Arg>()))>
+ /// is_nothrow_constructible
+ template<typename _Tp, typename... _Args>
+ struct is_nothrow_constructible
+ : public __is_nothrow_constructible_impl<_Tp, _Args...>::type
{ };
+ /// is_nothrow_default_constructible
template<typename _Tp>
- struct __is_nt_constructible_impl<_Tp>
- : public is_nothrow_default_constructible<_Tp>
+ struct is_nothrow_default_constructible
+ : public __is_nothrow_constructible_impl<_Tp>::type
{ };
- /// is_nothrow_constructible
- template<typename _Tp, typename... _Args>
- struct is_nothrow_constructible
- : public __and_<is_constructible<_Tp, _Args...>,
- __is_nt_constructible_impl<_Tp, _Args...>>
- { };
template<typename _Tp, bool = __is_referenceable<_Tp>::value>
struct __is_nothrow_copy_constructible_impl;
diff --git a/libstdc++-v3/testsuite/20_util/is_nothrow_constructible/94003.cc b/libstdc++-v3/testsuite/20_util/is_nothrow_constructible/94003.cc
new file mode 100644
index 00000000000..392a0878ba5
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_nothrow_constructible/94003.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2020 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 <optional>
+#include <tuple>
+
+template <bool B> struct abc {};
+
+template <typename T>
+
+struct future : public abc<std::is_trivially_constructible_v<std::tuple<T>>> {};
+
+class mutation {
+ mutation();
+ friend class std::optional<mutation>;
+};
+
+using mutation_opt = std::optional<mutation>;
+
+future<mutation_opt> foo();
+
+template <typename Consumer> future<mutation_opt> consume_partitions() {
+ return foo();
+}
+
+future<mutation_opt> bar() { return consume_partitions<int>(); }
+
+future<mutation> zed();
+future<mutation> apply_counter_update() { return zed(); }
diff --git a/libstdc++-v3/testsuite/20_util/is_nothrow_default_constructible/96999.cc b/libstdc++-v3/testsuite/20_util/is_nothrow_default_constructible/96999.cc
new file mode 100644
index 00000000000..9ec42760051
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_nothrow_default_constructible/96999.cc
@@ -0,0 +1,54 @@
+// Copyright (C) 2020 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 } }
+
+// PR libstdc++/96999
+
+#include <variant>
+#include <string>
+
+struct Foo {
+public:
+ explicit Foo(int) noexcept {}
+ Foo(Foo &&) noexcept = default;
+ Foo &operator=(Foo &&) = default;
+private:
+ Foo() noexcept {}
+};
+
+struct Boo {
+public:
+ explicit Boo(int) noexcept {}
+ Boo(Boo &&) noexcept = default;
+ Boo &operator=(Boo &&) = default;
+private:
+ Boo() noexcept {}
+};
+
+
+template<bool X>
+std::variant<Foo, Boo> g(int v, int x) {
+ return v == 0 ? std::variant<Foo, Boo>{Foo{x}} :
+ std::variant<Foo, Boo>{Boo{x}};
+}
+
+int main()
+{
+ std::variant<std::variant<Foo, Boo>, std::string> err{std::string("aaa")};
+}
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