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libstdc++: Simplify std::vector::vector(from_range_t, const Alloc&)

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Tomasz suggested replacing this constructor with just append_range(rg),
after using a delegating constructor so that the destructor will run if
append_range exits via an exception.

This is slightly less simple than his suggestion, because I want to
avoid the overhead of reserve's slow path and the ASan annotations.
Neither of those is needed for this constructor, because we have no
existing storage to reallocate and no unused capacity to tell ASan
about.

libstdc++-v3/ChangeLog:

	* include/bits/stl_vector.h (vector(from_range_t, Alloc)): Use
	delegating constructor instead of RAII guards. Use append_range
	for unsized input range case.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
This commit is contained in:
Jonathan Wakely 2025-03-20 09:52:35 +00:00 • committed by Jonathan Wakely
parent 3355e44dd2
commit 3e1d760bf4
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1 changed files with 2 additions and 18 deletions
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20
libstdc++-v3/include/bits/stl_vector.h
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@ -758,7 +758,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
template<__detail::__container_compatible_range<_Tp> _Rg>
constexpr
vector(from_range_t, _Rg&& __rg, const _Alloc& __a = _Alloc())
: _Base(__a)
: vector(__a)
{
if constexpr (ranges::forward_range<_Rg> || ranges::sized_range<_Rg>)
{
@ -766,28 +766,12 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
pointer __start =
this->_M_allocate(_S_check_init_len(__n,
_M_get_Tp_allocator()));
_Guard_alloc __guard(__start, __n, *this);
this->_M_impl._M_finish = this->_M_impl._M_start = __start;
this->_M_impl._M_end_of_storage = __start + __n;
_Base::_M_append_range(__rg);
(void) __guard._M_release();
}
else
{
// If an exception is thrown ~_Base() will deallocate storage,
// but will not destroy elements. This RAII type destroys them.
struct _Clear
{
constexpr ~_Clear() { if (_M_this) _M_this->clear(); }
vector* _M_this;
} __guard{this};
auto __first = ranges::begin(__rg);
const auto __last = ranges::end(__rg);
for (; __first != __last; ++__first)
emplace_back(*__first);
__guard._M_this = nullptr;
}
append_range(std::move(__rg));
}
#endif