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PR libstdc++/79254 simplify exception-safety in copy assignment

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PR libstdc++/79254
	* config/abi/pre/gnu.ver: Remove recently added symbols.
	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
	(basic_string::_M_copy_assign): Remove.
	(basic_string::operator=(const basic_string&)): Don't dispatch to
	_M_copy_assign. If source object is small just deallocate, otherwise
	perform new allocation before making any changes.
	* include/bits/basic_string.tcc [_GLIBCXX_USE_CXX11_ABI]
	(basic_string::_M_copy_assign(const basic_string&, true_type)):
	Remove.
	* testsuite/21_strings/basic_string/allocator/char/copy_assign.cc:
	Test cases where the allocators are equal or the string is small.
	* testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc:
	Likewise.

From-SVN: r245085
This commit is contained in:
Jonathan Wakely 2017-02-01 11:41:48 +00:00 • committed by Jonathan Wakely
parent a0deb99254
commit 11d10beb57
6 changed files with 65 additions and 81 deletions
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17
libstdc++-v3/ChangeLog
View file

@ -1,3 +1,20 @@
2017-02-01 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/79254
* config/abi/pre/gnu.ver: Remove recently added symbols.
* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI]
(basic_string::_M_copy_assign): Remove.
(basic_string::operator=(const basic_string&)): Don't dispatch to
_M_copy_assign. If source object is small just deallocate, otherwise
perform new allocation before making any changes.
* include/bits/basic_string.tcc [_GLIBCXX_USE_CXX11_ABI]
(basic_string::_M_copy_assign(const basic_string&, true_type)):
Remove.
* testsuite/21_strings/basic_string/allocator/char/copy_assign.cc:
Test cases where the allocators are equal or the string is small.
* testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc:
Likewise.
2017-01-30 Ville Voutilainen <ville.voutilainen@gmail.com>
Implement LWG 2825, LWG 2756 breaks class template argument

3
libstdc++-v3/config/abi/pre/gnu.ver
View file

@ -1955,9 +1955,6 @@ GLIBCXX_3.4.23 {
_ZNSsC[12]ERKSs[jmy]RKSaIcE;
_ZNSbIwSt11char_traitsIwESaIwEEC[12]ERKS2_mRKS1_;
# basic_string<C, T, A>::_M_copy_assign(const basic_string&, {true,false}_type)
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE14_M_copy_assign*;
#ifndef HAVE_EXCEPTION_PTR_SINCE_GCC46
# std::future symbols are exported in the first version to support
# std::exception_ptr

42
libstdc++-v3/include/bits/basic_string.h
View file

@ -393,15 +393,6 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
void
_M_erase(size_type __pos, size_type __n);
#if __cplusplus >= 201103L
void
_M_copy_assign(const basic_string& __str, /* pocca = */ true_type);
void
_M_copy_assign(const basic_string& __str, /* pocca = */ false_type)
{ this->_M_assign(__str); }
#endif
public:
// Construct/copy/destroy:
// NB: We overload ctors in some cases instead of using default
@ -636,12 +627,35 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
operator=(const basic_string& __str)
{
#if __cplusplus >= 201103L
_M_copy_assign(__str,
typename _Alloc_traits::propagate_on_container_copy_assignment());
#else
this->_M_assign(__str);
if (_Alloc_traits::_S_propagate_on_copy_assign())
{
if (!_Alloc_traits::_S_always_equal() && !_M_is_local()
&& _M_get_allocator() != __str._M_get_allocator())
{
// Propagating allocator cannot free existing storage so must
// deallocate it before replacing current allocator.
if (__str.size() <= _S_local_capacity)
{
_M_destroy(_M_allocated_capacity);
_M_data(_M_local_data());
_M_set_length(0);
}
else
{
const auto __len = __str.size();
auto __alloc = __str._M_get_allocator();
// If this allocation throws there are no effects:
auto __ptr = _Alloc_traits::allocate(__alloc, __len + 1);
_M_destroy(_M_allocated_capacity);
_M_data(__ptr);
_M_capacity(__len);
_M_set_length(__len);
}
}
std::__alloc_on_copy(_M_get_allocator(), __str._M_get_allocator());
}
#endif
return *this;
return this->assign(__str);
}
/**

64
libstdc++-v3/include/bits/basic_string.tcc
View file

@ -275,70 +275,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
}
}
#if __cplusplus >= 201103L
template<typename _CharT, typename _Traits, typename _Alloc>
void
basic_string<_CharT, _Traits, _Alloc>::
_M_copy_assign(const basic_string& __str, true_type)
{
struct _Guard // RAII type for strong exception-safety guarantee.
{
// Takes ownership of string's original state.
_Guard(basic_string* __self)
: _M_self(__self), _M_alloc(std::move(__self->_M_get_allocator())),
_M_ptr(__self->_M_data()),
_M_capacity(__self->_M_allocated_capacity), _M_len(__self->length())
{
__self->_M_data(__self->_M_local_data());
__self->_M_length(0);
}
// Restores string's original state if _M_release() was not called.
~_Guard()
{
if (_M_ptr)
{
_M_self->_M_get_allocator() = std::move(_M_alloc);
_M_self->_M_data(_M_ptr);
_M_self->_M_capacity(_M_capacity);
_M_self->_M_length(_M_len);
}
}
_Guard(const _Guard&) = delete;
_Guard& operator=(const _Guard&) = delete;
void _M_release()
{
// Original state can be freed now.
_Alloc_traits::deallocate(_M_alloc, _M_ptr, _M_capacity + 1);
_M_ptr = nullptr;
}
basic_string* _M_self;
allocator_type _M_alloc;
pointer _M_ptr;
size_type _M_capacity;
size_type _M_len;
};
if (!_Alloc_traits::_S_always_equal() && !_M_is_local()
&& _M_get_allocator() != __str._M_get_allocator())
{
// The propagating allocator cannot free existing storage.
_Guard __guard(this);
_M_get_allocator() = __str._M_get_allocator();
this->_M_assign(__str);
__guard._M_release();
}
else
{
_M_get_allocator() = __str._M_get_allocator();
this->_M_assign(__str);
}
}
#endif
template<typename _CharT, typename _Traits, typename _Alloc>
void
basic_string<_CharT, _Traits, _Alloc>::

10
libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/copy_assign.cc
View file

@ -121,6 +121,16 @@ void test03()
VERIFY( caught );
VERIFY( v1 == s1 );
VERIFY( v1.get_allocator() == a1 );
throw_alloc::set_limit(1); // Allow one more allocation (and no more).
test_type v3(s1, a1);
// No allocation when allocators are equal and capacity is sufficient:
VERIFY( v1.capacity() >= v3.size() );
v1 = v3;
// No allocation when the contents fit in the small-string buffer:
v2 = "sso";
v1 = v2;
VERIFY( v1.get_allocator() == a2 );
}
int main()

10
libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/copy_assign.cc
View file

@ -121,6 +121,16 @@ void test03()
VERIFY( caught );
VERIFY( v1 == s1 );
VERIFY( v1.get_allocator() == a1 );
throw_alloc::set_limit(1); // Allow one more allocation (and no more).
test_type v3(s1, a1);
// No allocation when allocators are equal and capacity is sufficient:
VERIFY( v1.capacity() >= v3.size() );
v1 = v3;
// No allocation when the contents fit in the small-string buffer:
v2 = L"sso";
v1 = v2;
VERIFY( v1.get_allocator() == a2 );
}
int main()