commit 5e6bb61638e06b51291307e7e21745a55feed5f2
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Tue Jan 31 17:56:03 2017 +0000
PR libstdc++/79254 simplify exception-safety in copy assignment
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.
@@ -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
@@ -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);
}
/**
@@ -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>::
@@ -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()
@@ -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()