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<xstring>: constexpr string element lifetime (#3334)
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@CaseyCarter
CaseyCarter authored Jan 12, 2023
1 parent ed9a3a0 commit 72229ff
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Showing 3 changed files with 28 additions and 63 deletions.
77 changes: 28 additions & 49 deletions stl/inc/xstring
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Original file line number Diff line number Diff line change
Expand Up @@ -2286,7 +2286,7 @@ public:
}

constexpr void _Activate_SSO_buffer() noexcept {
// begin the lifetime of the array elements (e.g., before copying into them)
// start the lifetime of the array elements
#if _HAS_CXX20
if (_STD is_constant_evaluated()) {
for (size_type _Idx = 0; _Idx < _BUF_SIZE; ++_Idx) {
Expand Down Expand Up @@ -2629,6 +2629,21 @@ public:
}

private:
static constexpr void _Start_element_lifetimes(_Elem* const _Ptr, const size_type _Size) {
// Start element lifetimes to avoid UB. This is a more general mechanism than _String_val::_Activate_SSO_buffer,
// but likely more impactful to throughput.
#if _HAS_CXX20
if (_STD is_constant_evaluated()) {
for (size_type _Idx = 0; _Idx < _Size; ++_Idx) {
_STD construct_at(_Ptr + _Idx);
}
}
#else // ^^^ C++20-or-later / pre-C++20 vvv
(void) _Ptr;
(void) _Size;
#endif // _HAS_CXX20
}

enum class _Construct_strategy : uint8_t { _From_char, _From_ptr, _From_string };

template <_Construct_strategy _Strat, class _Char_or_ptr>
Expand Down Expand Up @@ -2658,13 +2673,13 @@ private:
_Traits::assign(_My_data._Bx._Buf, _Count, _Arg);
_Traits::assign(_My_data._Bx._Buf[_Count], _Elem());
} else if constexpr (_Strat == _Construct_strategy::_From_ptr) {
_Traits::move(_My_data._Bx._Buf, _Arg, _Count);
_Traits::copy(_My_data._Bx._Buf, _Arg, _Count);
_Traits::assign(_My_data._Bx._Buf[_Count], _Elem());
} else { // _Strat == _Construct_strategy::_From_string
#ifdef _INSERT_STRING_ANNOTATION
_Traits::move(_My_data._Bx._Buf, _Arg, _Count + 1);
_Traits::copy(_My_data._Bx._Buf, _Arg, _Count + 1);
#else // ^^^ _INSERT_STRING_ANNOTATION / !_INSERT_STRING_ANNOTATION vvv
_Traits::move(_My_data._Bx._Buf, _Arg, _BUF_SIZE);
_Traits::copy(_My_data._Bx._Buf, _Arg, _BUF_SIZE);
#endif // !_INSERT_STRING_ANNOTATION
}

Expand All @@ -2677,11 +2692,7 @@ private:
const pointer _New_ptr = _Al.allocate(_New_capacity + 1); // throws
_Construct_in_place(_My_data._Bx._Ptr, _New_ptr);

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_capacity + 1);

_My_data._Mysize = _Count;
_My_data._Myres = _New_capacity;
Expand Down Expand Up @@ -2725,11 +2736,7 @@ private:
_Construct_in_place(_My_data._Bx._Ptr, _New_ptr);
_My_data._Myres = _New_capacity;

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_capacity + 1);
}
}

Expand All @@ -2745,11 +2752,7 @@ private:
const size_type _New_capacity = _Calculate_growth(_My_data._Mysize);
const pointer _New_ptr = _Al.allocate(_New_capacity + 1); // throws

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_capacity + 1);
_Traits::copy(_Unfancy(_New_ptr), _Old_ptr, _My_data._Mysize);
if (_My_data._Myres >= _BUF_SIZE) { // Need to deallocate old storage
_Al.deallocate(_My_data._Bx._Ptr, _My_data._Myres + 1);
Expand Down Expand Up @@ -2834,11 +2837,7 @@ public:
_Ptr = _Unfancy(_Fancyptr);
_Construct_in_place(_My_data._Bx._Ptr, _Fancyptr);

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Ptr, _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Ptr, _New_capacity + 1);
}

_My_data._Mysize = _New_size;
Expand Down Expand Up @@ -2909,11 +2908,7 @@ public:
_Container_proxy_ptr<_Alty> _Proxy(_Alproxy, _My_data); // throws
const pointer _Fancyptr = _Getal().allocate(_New_capacity + 1); // throws
// nothrow hereafter
#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_Fancyptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_Fancyptr), _New_capacity + 1);
_Construct_in_place(_My_data._Bx._Ptr, _Fancyptr);
_My_data._Mysize = _New_size;
_My_data._Myres = _New_capacity;
Expand Down Expand Up @@ -3217,11 +3212,7 @@ public:
auto _Right_al_non_const = _Right_al;
const auto _New_ptr = _Right_al_non_const.allocate(_New_capacity + 1); // throws

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_size + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_size + 1);

_Traits::copy(_Unfancy(_New_ptr), _Unfancy(_Right._Mypair._Myval2._Bx._Ptr), _New_size + 1);
_Tidy_deallocate();
Expand Down Expand Up @@ -4049,11 +4040,7 @@ public:
const pointer _New_ptr = _Al.allocate(_Target_capacity + 1); // throws
_ASAN_STRING_REMOVE(*this);

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _Target_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _Target_capacity + 1);

_My_data._Orphan_all();
_Traits::copy(_Unfancy(_New_ptr), _Unfancy(_My_data._Bx._Ptr), _My_data._Mysize + 1);
Expand Down Expand Up @@ -4792,11 +4779,7 @@ private:
auto& _Al = _Getal();
const pointer _New_ptr = _Al.allocate(_New_capacity + 1); // throws

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_capacity + 1);
_Mypair._Myval2._Orphan_all();
_ASAN_STRING_REMOVE(*this);
_Mypair._Myval2._Mysize = _New_size;
Expand Down Expand Up @@ -4829,11 +4812,7 @@ private:
auto& _Al = _Getal();
const pointer _New_ptr = _Al.allocate(_New_capacity + 1); // throws

#if _HAS_CXX20
if (_STD is_constant_evaluated()) { // Begin the lifetimes of the objects before copying to avoid UB
_Traits::assign(_Unfancy(_New_ptr), _New_capacity + 1, _Elem());
}
#endif // _HAS_CXX20
_Start_element_lifetimes(_Unfancy(_New_ptr), _New_capacity + 1);
_My_data._Orphan_all();
_ASAN_STRING_REMOVE(*this);
_My_data._Mysize = _New_size;
Expand Down
7 changes: 0 additions & 7 deletions tests/libcxx/expected_results.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -1009,7 +1009,6 @@ std/ranges/range.adaptors/range.lazy.split/view_interface.pass.cpp FAIL
std/ranges/range.adaptors/range.take/adaptor.pass.cpp FAIL
std/ranges/range.factories/range.single.view/cpo.pass.cpp FAIL
std/strings/basic.string/string.cons/dtor.pass.cpp FAIL
std/strings/basic.string/string.cons/implicit_deduction_guides.pass.cpp FAIL
std/strings/basic.string/string.modifiers/string_erase/iter.pass.cpp:0 FAIL
std/strings/basic.string/string.modifiers/string_erase/iter_iter.pass.cpp:0 FAIL
std/strings/basic.string/string.modifiers/string_insert/iter_iter_iter.pass.cpp:0 FAIL
Expand All @@ -1020,12 +1019,6 @@ std/strings/basic.string/string.modifiers/string_replace/iter_iter_pointer_size.
std/strings/basic.string/string.modifiers/string_replace/iter_iter_size_char.pass.cpp:0 FAIL
std/strings/basic.string/string.modifiers/string_replace/iter_iter_string.pass.cpp:0 FAIL
std/strings/basic.string/string.modifiers/string_replace/iter_iter_string_view.pass.cpp:0 FAIL
std/strings/string.view/string.view.comparison/equal.pass.cpp FAIL
std/strings/string.view/string.view.comparison/greater.pass.cpp FAIL
std/strings/string.view/string.view.comparison/greater_equal.pass.cpp FAIL
std/strings/string.view/string.view.comparison/less.pass.cpp FAIL
std/strings/string.view/string.view.comparison/less_equal.pass.cpp FAIL
std/strings/string.view/string.view.comparison/not_equal.pass.cpp FAIL
std/thread/futures/futures.task/futures.task.members/ctor2.compile.pass.cpp FAIL
std/utilities/function.objects/func.wrap/func.wrap.func/addressof.pass.cpp:0 FAIL
std/utilities/function.objects/func.wrap/func.wrap.func/func.wrap.func.alg/swap.pass.cpp:0 FAIL
Expand Down
7 changes: 0 additions & 7 deletions tests/libcxx/skipped_tests.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -1009,7 +1009,6 @@ ranges\range.adaptors\range.lazy.split\view_interface.pass.cpp
ranges\range.adaptors\range.take\adaptor.pass.cpp
ranges\range.factories\range.single.view\cpo.pass.cpp
strings\basic.string\string.cons\dtor.pass.cpp
strings\basic.string\string.cons\implicit_deduction_guides.pass.cpp
strings\basic.string\string.modifiers\string_erase\iter.pass.cpp
strings\basic.string\string.modifiers\string_erase\iter_iter.pass.cpp
strings\basic.string\string.modifiers\string_insert\iter_iter_iter.pass.cpp
Expand All @@ -1020,12 +1019,6 @@ strings\basic.string\string.modifiers\string_replace\iter_iter_pointer_size.pass
strings\basic.string\string.modifiers\string_replace\iter_iter_size_char.pass.cpp
strings\basic.string\string.modifiers\string_replace\iter_iter_string.pass.cpp
strings\basic.string\string.modifiers\string_replace\iter_iter_string_view.pass.cpp
strings\string.view\string.view.comparison\equal.pass.cpp
strings\string.view\string.view.comparison\greater.pass.cpp
strings\string.view\string.view.comparison\greater_equal.pass.cpp
strings\string.view\string.view.comparison\less.pass.cpp
strings\string.view\string.view.comparison\less_equal.pass.cpp
strings\string.view\string.view.comparison\not_equal.pass.cpp
thread\futures\futures.task\futures.task.members\ctor2.compile.pass.cpp
utilities\function.objects\func.wrap\func.wrap.func\addressof.pass.cpp
utilities\function.objects\func.wrap\func.wrap.func\func.wrap.func.alg\swap.pass.cpp
Expand Down

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