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libstdc++: Implement P0966 std::string::reserve should not shrink

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Remove ability for reserve(n) to reduce a string's capacity. Add a new
reserve() overload that makes a shrink-to-fit request, and make
shrink_to_fit() use that.

libstdc++-v3/ChangeLog:

2020-07-30  Andrew Luo  <andrewluotechnologies@outlook.com>
	    Jonathan Wakely  <jwakely@redhat.com>

	* config/abi/pre/gnu.ver (GLIBCXX_3.4): Use less greedy
	patterns for basic_string members.
	(GLIBCXX_3.4.29): Export new basic_string::reserve symbols.
	* doc/xml/manual/status_cxx2020.xml: Update P0966 status.
	* include/bits/basic_string.h (shrink_to_fit()): Call reserve().
	(reserve(size_type)): Remove default argument.
	(reserve()): Declare new overload.
	[!_GLIBCXX_USE_CXX11_ABI] (shrink_to_fit, reserve): Likewise.
	* include/bits/basic_string.tcc (reserve(size_type)): Remove
	support for shrinking capacity.
	(reserve()): Perform shrink-to-fit operation.
	[!_GLIBCXX_USE_CXX11_ABI] (reserve): Likewise.
	* testsuite/21_strings/basic_string/capacity/1.cc: Adjust to
	reflect new behavior.
	* testsuite/21_strings/basic_string/capacity/char/1.cc:
	Likewise.
	* testsuite/21_strings/basic_string/capacity/char/18654.cc:
	Likewise.
	* testsuite/21_strings/basic_string/capacity/char/2.cc:
	Likewise.
	* testsuite/21_strings/basic_string/capacity/wchar_t/1.cc:
	Likewise.
	* testsuite/21_strings/basic_string/capacity/wchar_t/18654.cc:
	Likewise.
	* testsuite/21_strings/basic_string/capacity/wchar_t/2.cc:
	Likewise.
This commit is contained in:
Andrew Luo 2020-08-06 19:35:43 +01:00 committed by Jonathan Wakely
parent 4e39f563c0
commit 140cf935cd
11 changed files with 182 additions and 79 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
libstdc++-v3/config/abi/pre/gnu.ver
View File

@ -223,7 +223,10 @@ GLIBCXX_3.4 {
_ZNSs6assignE[PRcjmvy]*;
_ZNSs6insertE[PRcjmvy]*;
_ZNSs6insertEN9__gnu_cxx17__normal_iteratorIPcSsEE[PRcjmvy]*;
_ZNSs[67][j-z]*E[PRcjmvy]*;
_ZNSs6rbeginEv;
_ZNSs6resizeE[jmy]*;
_ZNSs7replaceE[jmy]*;
_ZNSs7reserveE[jmy];
_ZNSs7[a-z]*EES2_[NPRjmy]*;
_ZNSs7[a-z]*EES2_S[12]*;
_ZNSs12_Alloc_hiderC*;
@ -290,7 +293,10 @@ GLIBCXX_3.4 {
_ZNSbIwSt11char_traitsIwESaIwEE6assignE[PRwjmvy]*;
_ZNSbIwSt11char_traitsIwESaIwEE6insertE[PRwjmvy]*;
_ZNSbIwSt11char_traitsIwESaIwEE6insertEN9__gnu_cxx17__normal_iteratorIPwS2_EE[PRwjmvy]*;
_ZNSbIwSt11char_traitsIwESaIwEE[67][j-z]*E[PRwjmvy]*;
_ZNSbIwSt11char_traitsIwESaIwEE6rbeginEv;
_ZNSbIwSt11char_traitsIwESaIwEE7replaceEmm[PRm]*;
_ZNSbIwSt11char_traitsIwESaIwEE6resizeEm*;
_ZNSbIwSt11char_traitsIwESaIwEE7reserveEm;
_ZNSbIwSt11char_traitsIwESaIwEE7[a-z]*EES6_[NPRjmy]*;
_ZNSbIwSt11char_traitsIwESaIwEE7[a-z]*EES6_S[56]*;
_ZNSbIwSt11char_traitsIwESaIwEE12_Alloc_hiderC*;
@ -1740,7 +1746,7 @@ GLIBCXX_3.4.21 {
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE6rbegin*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE6resize*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE7replace*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE7reserve*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE7reserveE[jmy];
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE8pop_back*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE9push_back*;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE[7-9]_[MS]_*;
@ -2309,6 +2315,11 @@ GLIBCXX_3.4.29 {
# std::__istream_extract(wistream&, wchar_t*, streamsize)
_ZSt17__istream_extractIwSt11char_traitsIwEEvRSt13basic_istreamIT_T0_EPS3_[ilx];
# basic_string::reserve()
_ZNSs7reserveEv;
_ZNSbIwSt11char_traitsIwESaIwEE7reserveEv;
_ZNSt7__cxx1112basic_stringI[cw]St11char_traitsI[cw]ESaI[cw]EE7reserveEv;
} GLIBCXX_3.4.28;
# Symbols in the support library (libsupc++) have their own tag.

3
libstdc++-v3/doc/xml/manual/status_cxx2020.xml
View File

@ -635,13 +635,12 @@ or any notes about the implementation.
</row>
<row>
<?dbhtml bgcolor="#C8B0B0" ?>
<entry> <code>string::reserve</code> Should Not Shrink </entry>
<entry>
<link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0966r1.html">
P0966R1 </link>
</entry>
<entry align="center"> </entry>
<entry align="center"> 11 </entry>
<entry />
</row>

52
libstdc++-v3/include/bits/basic_string.h
View File

@ -940,20 +940,13 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
{ this->resize(__n, _CharT()); }
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
/// A non-binding request to reduce capacity() to size().
void
shrink_to_fit() noexcept
{
#if __cpp_exceptions
if (capacity() > size())
{
try
{ reserve(0); }
catch(...)
{ }
}
#endif
}
{ reserve(); }
#pragma GCC diagnostic pop
#endif
/**
@ -985,7 +978,16 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
* data.
*/
void
reserve(size_type __res_arg = 0);
reserve(size_type __res_arg);
/**
* Equivalent to shrink_to_fit().
*/
#if __cplusplus > 201703L
[[deprecated("use shrink_to_fit() instead")]]
#endif
void
reserve();
/**
* Erases the string, making it empty.
@ -3942,20 +3944,13 @@ _GLIBCXX_END_NAMESPACE_CXX11
{ this->resize(__n, _CharT()); }
#if __cplusplus >= 201103L
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
/// A non-binding request to reduce capacity() to size().
void
shrink_to_fit() _GLIBCXX_NOEXCEPT
{
#if __cpp_exceptions
if (capacity() > size())
{
try
{ reserve(0); }
catch(...)
{ }
}
#endif
}
shrink_to_fit() noexcept
{ reserve(); }
#pragma GCC diagnostic pop
#endif
/**
@ -3984,7 +3979,14 @@ _GLIBCXX_END_NAMESPACE_CXX11
* data.
*/
void
reserve(size_type __res_arg = 0);
reserve(size_type __res_arg);
/// Equivalent to shrink_to_fit().
#if __cplusplus > 201703L
[[deprecated("use shrink_to_fit() instead")]]
#endif
void
reserve();
/**
* Erases the string, making it empty.

119
libstdc++-v3/include/bits/basic_string.tcc
View File

@ -280,29 +280,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
basic_string<_CharT, _Traits, _Alloc>::
reserve(size_type __res)
{
// Make sure we don't shrink below the current size.
if (__res < length())
__res = length();
const size_type __capacity = capacity();
if (__res != __capacity)
{
if (__res > __capacity
|| __res > size_type(_S_local_capacity))
{
pointer __tmp = _M_create(__res, __capacity);
this->_S_copy(__tmp, _M_data(), length() + 1);
_M_dispose();
_M_data(__tmp);
_M_capacity(__res);
}
else if (!_M_is_local())
{
this->_S_copy(_M_local_data(), _M_data(), length() + 1);
_M_destroy(__capacity);
_M_data(_M_local_data());
}
}
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2968. Inconsistencies between basic_string reserve and
// vector/unordered_map/unordered_set reserve functions
// P0966 reserve should not shrink
if (__res <= __capacity)
return;
pointer __tmp = _M_create(__res, __capacity);
this->_S_copy(__tmp, _M_data(), length() + 1);
_M_dispose();
_M_data(__tmp);
_M_capacity(__res);
}
template<typename _CharT, typename _Traits, typename _Alloc>
@ -342,6 +332,41 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_M_set_length(length() - __n);
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
basic_string<_CharT, _Traits, _Alloc>::
reserve()
{
if (_M_is_local())
return;
const size_type __length = length();
const size_type __capacity = _M_allocated_capacity;
if (__length <= size_type(_S_local_capacity))
{
this->_S_copy(_M_local_data(), _M_data(), __length + 1);
_M_destroy(__capacity);
_M_data(_M_local_data());
}
#if __cpp_exceptions
else if (__length < __capacity)
try
{
pointer __tmp
= _Alloc_traits::allocate(_M_get_allocator(), __length + 1);
this->_S_copy(__tmp, _M_data(), __length + 1);
_M_dispose();
_M_data(__tmp);
_M_capacity(__length);
}
catch (const __cxxabiv1::__forced_unwind&)
{ throw; }
catch (...)
{ /* swallow the exception */ }
#endif
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
basic_string<_CharT, _Traits, _Alloc>::
@ -953,16 +978,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
basic_string<_CharT, _Traits, _Alloc>::
reserve(size_type __res)
{
if (__res != this->capacity() || _M_rep()->_M_is_shared())
{
// Make sure we don't shrink below the current size
if (__res < this->size())
__res = this->size();
const allocator_type __a = get_allocator();
_CharT* __tmp = _M_rep()->_M_clone(__a, __res - this->size());
_M_rep()->_M_dispose(__a);
_M_data(__tmp);
}
const size_type __capacity = capacity();
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2968. Inconsistencies between basic_string reserve and
// vector/unordered_map/unordered_set reserve functions
// P0966 reserve should not shrink
if (__res <= __capacity)
{
if (!_M_rep()->_M_is_shared())
return;
// unshare, but keep same capacity
__res = __capacity;
}
const allocator_type __a = get_allocator();
_CharT* __tmp = _M_rep()->_M_clone(__a, __res - this->size());
_M_rep()->_M_dispose(__a);
_M_data(__tmp);
}
template<typename _CharT, typename _Traits, typename _Alloc>
@ -1006,7 +1040,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// The standard places no restriction on allocating more memory
// than is strictly needed within this layer at the moment or as
// requested by an explicit application call to reserve().
// requested by an explicit application call to reserve(n).
// Many malloc implementations perform quite poorly when an
// application attempts to allocate memory in a stepwise fashion
@ -1140,6 +1174,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return *this;
}
template<typename _CharT, typename _Traits, typename _Alloc>
void
basic_string<_CharT, _Traits, _Alloc>::
reserve()
{
if (length() < capacity() || _M_rep()->_M_is_shared())
try
{
const allocator_type __a = get_allocator();
_CharT* __tmp = _M_rep()->_M_clone(__a);
_M_rep()->_M_dispose(__a);
_M_data(__tmp);
}
catch (const __cxxabiv1::__forced_unwind&)
{ throw; }
catch (...)
{ /* swallow the exception */ }
}
template<typename _CharT, typename _Traits, typename _Alloc>
typename basic_string<_CharT, _Traits, _Alloc>::size_type
basic_string<_CharT, _Traits, _Alloc>::

14
libstdc++-v3/testsuite/21_strings/basic_string/capacity/1.cc
View File

@ -136,13 +136,19 @@ void test01()
sz04 = str02.capacity();
VERIFY( sz04 >= sz03 );
VERIFY( sz04 >= 100 );
#if __cplusplus <= 201703L
str02.reserve();
sz03 = str02.capacity();
#if _GLIBCXX_USE_CXX11_ABI
VERIFY( sz03 < 100);
#else
VERIFY( sz03 == 0 );
str02.shrink_to_fit(); // reserve is deprecated in C++20
#endif
sz03 = str02.capacity();
VERIFY( sz03 < sz04 );
// P0966: reserve should not shrink
str02.reserve(100);
sz03 = str02.capacity();
str02.reserve(sz03 - 1);
VERIFY( str02.capacity() == sz03 );
sz03 = str02.size() + 5;
str02.resize(sz03);

14
libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/1.cc
View File

@ -33,13 +33,19 @@ void test01()
size_type_s sz02 = str01.capacity();
VERIFY( sz02 >= sz01 );
VERIFY( sz02 >= 100 );
#if __cplusplus <= 201703L
str01.reserve();
sz01 = str01.capacity();
#if _GLIBCXX_USE_CXX11_ABI
VERIFY( sz01 < 100);
#else
VERIFY( sz01 == 0 );
str01.shrink_to_fit(); // reserve is deprecated in C++20
#endif
sz01 = str01.capacity();
VERIFY( sz01 < sz02 );
// P0966: reserve should not shrink
str01.reserve(100);
sz01 = str01.capacity();
str01.reserve(sz01 - 1);
VERIFY( str01.capacity() == sz01 );
sz01 = str01.size() + 5;
str01.resize(sz01);

8
libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/18654.cc
View File

@ -47,11 +47,17 @@ void test01()
{
string str(i, 'x');
str.reserve(3 * i);
const size_type cap = str.capacity();
VERIFY( cap >= 3 * i );
str.reserve(2 * i);
VERIFY( str.capacity() == 2 * i );
VERIFY( str.capacity() == cap );
#if __cplusplus <= 201703L
str.reserve();
#else
str.shrink_to_fit(); // reserve is deprecated in C++20
#endif
VERIFY( str.capacity() == i );
}
}

6
libstdc++-v3/testsuite/21_strings/basic_string/capacity/char/2.cc
View File

@ -29,7 +29,11 @@ void test02()
std::string str01 = "twelve chars";
// str01 becomes shared
std::string str02 = str01;
str01.reserve(1);
#if __cplusplus <= 201703L
str01.reserve();
#else
str01.shrink_to_fit(); // reserve is deprecated in C++20
#endif
VERIFY( str01.capacity() >= 12 );
}

14
libstdc++-v3/testsuite/21_strings/basic_string/capacity/wchar_t/1.cc
View File

@ -33,13 +33,19 @@ void test01()
size_type_s sz02 = str01.capacity();
VERIFY( sz02 >= sz01 );
VERIFY( sz02 >= 100 );
#if __cplusplus <= 201703L
str01.reserve();
sz01 = str01.capacity();
#if _GLIBCXX_USE_CXX11_ABI
VERIFY( sz01 < 100);
#else
VERIFY( sz01 == 0 );
str01.shrink_to_fit(); // reserve is deprecated in C++20
#endif
sz01 = str01.capacity();
VERIFY( sz01 < sz02 );
// P0966: reserve should not shrink
str01.reserve(100);
sz01 = str01.capacity();
str01.reserve(sz01 - 1);
VERIFY( str01.capacity() == sz01 );
sz01 = str01.size() + 5;
str01.resize(sz01);

8
libstdc++-v3/testsuite/21_strings/basic_string/capacity/wchar_t/18654.cc
View File

@ -47,11 +47,17 @@ void test01()
{
wstring str(i, L'x');
str.reserve(3 * i);
const size_type cap = str.capacity();
VERIFY( cap >= 3 * i );
str.reserve(2 * i);
VERIFY( str.capacity() == 2 * i );
VERIFY( str.capacity() == cap );
#if __cplusplus <= 201703L
str.reserve();
#else
str.shrink_to_fit(); // reserve is deprecated in C++20
#endif
VERIFY( str.capacity() == i );
}
}

6
libstdc++-v3/testsuite/21_strings/basic_string/capacity/wchar_t/2.cc
View File

@ -29,7 +29,11 @@ void test02()
std::wstring str01 = L"twelve chars";
// str01 becomes shared
std::wstring str02 = str01;
str01.reserve(1);
#if __cplusplus <= 201703L
str01.reserve();
#else
str01.shrink_to_fit(); // reserve is deprecated in C++20
#endif
VERIFY( str01.capacity() == 12 );
}