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PR libstdc++/58265 implement LWG 2063 for COW strings 

For COW strings the default constructor does not allocate when
_GLIBCXX_FULLY_DYNAMIC_STRING == 0, so can be noexcept. The move
constructor and swap do not allocate when the allocators are equal, so
add conditional noexcept using allocator_traits::is_always_equal.

	PR libstdc++/58265
	* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
	[_GLIBCXX_FULLY_DYNAMIC_STRING==0] (basic_string::basic_string()):
	Add GLIBCXX_NOEXCEPT.
	(basic_string::operator=(basic_string&&)): Add _GLIBCXX_NOEXCEPT_IF
	to depend on the allocator's is_always_equal property (LWG 2063).
	(basic_string::swap(basic_string&)): Likewise.
	* include/bits/basic_string.tcc [!_GLIBCXX_USE_CXX11_ABI]
	(basic_string::swap(basic_string&)): Likewise.
	* testsuite/21_strings/basic_string/allocator/char/move_assign.cc:
	Check is_nothrow_move_assignable.
	* testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc:
	Check is_nothrow_move_assignable.
	* testsuite/21_strings/basic_string/cons/char/
	noexcept_move_construct.cc: Likewise.
	* testsuite/21_strings/basic_string/cons/wchar_t/
	noexcept_move_construct.cc: Likewise.

From-SVN: r262443
This commit is contained in:
Jonathan Wakely 2018-07-05 16:56:06 +01:00 committed by Jonathan Wakely
parent 245471c67f
commit d8d9b83b33
7 changed files with 40 additions and 4 deletions
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20
libstdc++-v3/ChangeLog
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@ -1,3 +1,23 @@
2018-07-05 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/58265
* include/bits/basic_string.h [!_GLIBCXX_USE_CXX11_ABI]
[_GLIBCXX_FULLY_DYNAMIC_STRING==0] (basic_string::basic_string()):
Add GLIBCXX_NOEXCEPT.
(basic_string::operator=(basic_string&&)): Add _GLIBCXX_NOEXCEPT_IF
to depend on the allocator's is_always_equal property (LWG 2063).
(basic_string::swap(basic_string&)): Likewise.
* include/bits/basic_string.tcc [!_GLIBCXX_USE_CXX11_ABI]
(basic_string::swap(basic_string&)): Likewise.
* testsuite/21_strings/basic_string/allocator/char/move_assign.cc:
Check is_nothrow_move_assignable.
* testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc:
Check is_nothrow_move_assignable.
* testsuite/21_strings/basic_string/cons/char/
noexcept_move_construct.cc: Likewise.
* testsuite/21_strings/basic_string/cons/wchar_t/
noexcept_move_construct.cc: Likewise.
2018-07-04 Jonathan Wakely <jwakely@redhat.com>
P0646R1 Improving the Return Value of Erase-Like Algorithms I

9
libstdc++-v3/include/bits/basic_string.h
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@ -3486,6 +3486,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
*/
basic_string()
#if _GLIBCXX_FULLY_DYNAMIC_STRING == 0
_GLIBCXX_NOEXCEPT
: _M_dataplus(_S_empty_rep()._M_refdata(), _Alloc()) { }
#else
: _M_dataplus(_S_construct(size_type(), _CharT(), _Alloc()), _Alloc()){ }
@ -3642,7 +3643,7 @@ _GLIBCXX_END_NAMESPACE_CXX11
* @param __str Source string.
*/
basic_string&
operator=(const basic_string& __str)
operator=(const basic_string& __str)
{ return this->assign(__str); }
/**
@ -3675,9 +3676,9 @@ _GLIBCXX_END_NAMESPACE_CXX11
* The contents of @a str are moved into this string (without copying).
* @a str is a valid, but unspecified string.
**/
// PR 58265, this should be noexcept.
basic_string&
operator=(basic_string&& __str)
_GLIBCXX_NOEXCEPT_IF(allocator_traits<_Alloc>::is_always_equal::value)
{
// NB: DR 1204.
this->swap(__str);
@ -5111,9 +5112,9 @@ _GLIBCXX_END_NAMESPACE_CXX11
* Exchanges the contents of this string with that of @a __s in constant
* time.
*/
// PR 58265, this should be noexcept.
void
swap(basic_string& __s);
swap(basic_string& __s)
_GLIBCXX_NOEXCEPT_IF(allocator_traits<_Alloc>::is_always_equal::value);
// String operations:
/**

1
libstdc++-v3/include/bits/basic_string.tcc
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@ -967,6 +967,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
basic_string<_CharT, _Traits, _Alloc>::
swap(basic_string& __s)
_GLIBCXX_NOEXCEPT_IF(allocator_traits<_Alloc>::is_always_equal::value)
{
if (_M_rep()->_M_is_leaked())
_M_rep()->_M_set_sharable();

3
libstdc++-v3/testsuite/21_strings/basic_string/allocator/char/move_assign.cc
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@ -34,6 +34,9 @@ void test01()
typedef propagating_allocator<C, false> alloc_type;
typedef std::basic_string<C, traits, alloc_type> test_type;
static_assert(std::is_move_assignable<test_type>::value, "");
static_assert(!std::is_nothrow_move_assignable<test_type>::value, "");
test_type v1(alloc_type(1));
v1.assign(1, c);
test_type v2(alloc_type(2));

3
libstdc++-v3/testsuite/21_strings/basic_string/allocator/wchar_t/move_assign.cc
View File

@ -34,6 +34,9 @@ void test01()
typedef propagating_allocator<C, false> alloc_type;
typedef std::basic_string<C, traits, alloc_type> test_type;
static_assert(std::is_move_assignable<test_type>::value, "");
static_assert(!std::is_nothrow_move_assignable<test_type>::value, "");
test_type v1(alloc_type(1));
v1.assign(1, c);
test_type v2(alloc_type(2));

4
libstdc++-v3/testsuite/21_strings/basic_string/cons/char/noexcept_move_construct.cc
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@ -23,4 +23,8 @@
typedef std::string stype;
// True except for COW strings with _GLIBCXX_FULLY_DYNAMIC_STRING:
static_assert(std::is_nothrow_move_constructible<stype>::value, "Error");
// True for std::allocator because is_always_equal, but not true in general:
static_assert(std::is_nothrow_move_assignable<stype>::value, "lwg 2063");

4
libstdc++-v3/testsuite/21_strings/basic_string/cons/wchar_t/noexcept_move_construct.cc
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@ -23,4 +23,8 @@
typedef std::wstring wstype;
// True except for COW strings with _GLIBCXX_FULLY_DYNAMIC_STRING:
static_assert(std::is_nothrow_move_constructible<wstype>::value, "Error");
// True for std::allocator because is_always_equal, but not true in general:
static_assert(std::is_nothrow_move_assignable<wstype>::value, "lwg 2063");