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libstdc++: Ensure active union member is correctly set

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This patch ensures that the union members for std::string and
std::variant are always properly set when a change occurs.

libstdc++-v3/ChangeLog:

	* include/bits/basic_string.h: (basic_string(basic_string&&)):
	Activate _M_local_buf when needed.
	(basic_string(basic_string&&, const _Alloc&)): Likewise.
	* include/bits/basic_string.tcc: (basic_string::swap): Likewise.
	* include/std/variant: (__detail::__variant::__construct_n): New.
	(__detail::__variant::__emplace): Use __construct_n.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
This commit is contained in:
Nathaniel Shead 2023-09-29 10:30:41 +01:00 • committed by Jonathan Wakely
parent 346f599156
commit 28adad7a32
3 changed files with 38 additions and 4 deletions
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6
libstdc++-v3/include/bits/basic_string.h
View file

@ -678,6 +678,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{
if (__str._M_is_local())
{
(void)_M_use_local_data();
traits_type::copy(_M_local_buf, __str._M_local_buf,
__str.length() + 1);
}
@ -691,7 +692,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
// basic_stringbuf relies on writing into unallocated capacity so
// we mess up the contents if we put a '\0' in the string.
_M_length(__str.length());
__str._M_data(__str._M_local_data());
__str._M_data(__str._M_use_local_data());
__str._M_set_length(0);
}
@ -717,6 +718,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{
if (__str._M_is_local())
{
(void)_M_use_local_data();
traits_type::copy(_M_local_buf, __str._M_local_buf,
__str.length() + 1);
_M_length(__str.length());
@ -728,7 +730,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
_M_data(__str._M_data());
_M_length(__str.length());
_M_capacity(__str._M_allocated_capacity);
__str._M_data(__str._M_local_buf);
__str._M_data(__str._M_use_local_data());
__str._M_set_length(0);
}
else

4
libstdc++-v3/include/bits/basic_string.tcc
View file

@ -79,6 +79,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
else if (__s.length())
{
(void)_M_use_local_data();
traits_type::copy(_M_local_buf, __s._M_local_buf,
__s.length() + 1);
_M_length(__s.length());
@ -87,6 +88,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
else if (length())
{
(void)__s._M_use_local_data();
traits_type::copy(__s._M_local_buf, _M_local_buf,
length() + 1);
__s._M_length(length());
@ -97,6 +99,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
else
{
const size_type __tmp_capacity = __s._M_allocated_capacity;
(void)__s._M_use_local_data();
traits_type::copy(__s._M_local_buf, _M_local_buf,
length() + 1);
_M_data(__s._M_data());
@ -108,6 +111,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
const size_type __tmp_capacity = _M_allocated_capacity;
if (__s._M_is_local())
{
(void)_M_use_local_data();
traits_type::copy(_M_local_buf, __s._M_local_buf,
__s.length() + 1);
__s._M_data(_M_data());

32
libstdc++-v3/include/std/variant
View file

@ -320,6 +320,33 @@ namespace __variant
__get(_Variant&& __v) noexcept
{ return __variant::__get_n<_Np>(std::forward<_Variant>(__v)._M_u); }
// Gets the _Uninitialized to construct into for __u.
template<size_t _Np, typename _Union>
constexpr decltype(auto)
__construct_n(_Union& __u) noexcept
{
if constexpr (_Np == 0)
return &__u._M_first;
else if constexpr (_Np == 1)
{
std::_Construct(&__u._M_rest);
return &__u._M_rest._M_first;
}
else if constexpr (_Np == 2)
{
std::_Construct(&__u._M_rest);
std::_Construct(&__u._M_rest._M_rest);
return &__u._M_rest._M_rest._M_first;
}
else
{
std::_Construct(&__u._M_rest);
std::_Construct(&__u._M_rest._M_rest);
std::_Construct(&__u._M_rest._M_rest._M_rest);
return __variant::__construct_n<_Np - 3>(__u._M_rest._M_rest._M_rest);
}
}
template<typename... _Types>
struct _Traits
{
@ -536,8 +563,9 @@ namespace __variant
__emplace(_Variant_storage<_Triv, _Types...>& __v, _Args&&... __args)
{
__v._M_reset();
auto* __addr = std::__addressof(__variant::__get_n<_Np>(__v._M_u));
std::_Construct(__addr, std::forward<_Args>(__args)...);
auto* __addr = __variant::__construct_n<_Np>(__v._M_u);
std::_Construct(__addr, in_place_index<0>,
std::forward<_Args>(__args)...);
// Construction didn't throw, so can set the new index now:
__v._M_index = _Np;
}