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c++: fix triviality of class with unsatisfied op=

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cxx20_pair is trivially copyable because it has a trivial copy constructor
and only a deleted copy assignment operator; the non-triviality of the
unsatisfied copy assignment overload is not considered.

gcc/cp/ChangeLog:

	* class.cc (check_methods): Call constraints_satisfied_p.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/cond-triv3.C: New test.
This commit is contained in:
Jason Merrill 2022-09-29 13:45:02 -04:00
parent 13337ea9a1
commit 04d54b70fe
2 changed files with 55 additions and 2 deletions
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13
gcc/cp/class.cc
View file

@ -4795,8 +4795,9 @@ check_methods (tree t)
/* Check whether the eligible special member functions (P0848) are
user-provided. add_method arranged that the CLASSTYPE_MEMBER_VEC only
has the eligible ones; TYPE_FIELDS also contains ineligible overloads,
which is why this needs to be separate from the loop above. */
has the eligible ones, unless none are eligible; TYPE_FIELDS also contains
ineligible overloads, which is why this needs to be separate from the loop
above. */
if (tree dtor = CLASSTYPE_DESTRUCTOR (t))
{
@ -4819,6 +4820,10 @@ check_methods (tree t)
{
if (!user_provided_p (fn))
/* Might be trivial. */;
else if (TREE_CODE (fn) == TEMPLATE_DECL)
/* Templates are never special members. */;
else if (!constraints_satisfied_p (fn))
/* Not eligible. */;
else if (copy_fn_p (fn))
TYPE_HAS_COMPLEX_COPY_CTOR (t) = true;
else if (move_fn_p (fn))
@ -4829,6 +4834,10 @@ check_methods (tree t)
{
if (!user_provided_p (fn))
/* Might be trivial. */;
else if (TREE_CODE (fn) == TEMPLATE_DECL)
/* Templates are never special members. */;
else if (!constraints_satisfied_p (fn))
/* Not eligible. */;
else if (copy_fn_p (fn))
TYPE_HAS_COMPLEX_COPY_ASSIGN (t) = true;
else if (move_fn_p (fn))

44
gcc/testsuite/g++.dg/cpp2a/cond-triv3.C Normal file
View file

@ -0,0 +1,44 @@
// { dg-do compile { target c++20 } }
template<class T>
struct X
{
T first{};
X& operator=(const X&) = delete;
X& operator=(const X&) requires requires (T& t) { t = t; } { return *this; }
};
// C++20 std::pair<const int, int>:
using cxx20_pair = X<const int>;
static_assert( __is_trivially_constructible(cxx20_pair, const cxx20_pair&), "" );
static_assert( !__is_assignable(cxx20_pair&, const cxx20_pair&), "" );
static_assert( __is_trivially_copyable(cxx20_pair), "" );
template<bool, typename, typename F> struct conditional { using type = F; };
template<typename T, typename F> struct conditional<true, T, F> { using type = T; };
struct base
{
base() = default;
~base() = default;
base(const base&) = default;
base& operator=(const base&) = delete;
};
struct nope;
template<class T>
struct Y : base
{
T first{};
Y& operator=(typename conditional<__is_assignable(T&, const T&), const Y&, const nope&>::type)
{ return *this; }
};
// C++17 std::pair<const int, int>:
using cxx17_pair = Y<const int>;
static_assert( __is_trivially_constructible(cxx17_pair, const cxx17_pair&), "" );
static_assert( ! __is_assignable(cxx17_pair&, const cxx17_pair&), "" );
static_assert( __is_trivially_copyable(cxx17_pair), "???" );