From: Jonathan Wakely Date: Wed, 20 Jul 2022 15:51:44 +0000 (+0100) Subject: libstdc++: Fix std::common_iterator assignment [PR100823] X-Git-Tag: releases/gcc-10.5.0~175 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5d7de4c8fd9af68011e1fa7bc1d022db81d89594;p=thirdparty%2Fgcc.git libstdc++: Fix std::common_iterator assignment [PR100823] This fixes the following conformance problems reported in the PR: - Move constructor and move assignment should be defined. - Copy assignment from a valueless object should be allowed. Assignment is completely rewritten by this patch, as the previous version had a number of problems. The converting assignment failed to handle the case of assigning a new value to a valueless object, which should work. It only accepted lvalue arguments, so wasn't usable to implement the move assignment operator. Finally, it enforced the precondition that the argument is not valueless, which is correct for the converting assignment but not for the copy assignment. A new _M_assign member is added to handle all cases of assignment (copying from an lvalue, moving from an rvalue, and converting from a different type). The not valueless precondition is checked in the converting assignment before calling _M_assign, so isn't enforced for copy and move assignment. The new function no longer uses a switch, so handles valueless objects as the LHS or RHS of the assignment. libstdc++-v3/ChangeLog: PR libstdc++/100823 * include/bits/stl_iterator.h (common_iterator): Define move constructor and move assignment operator. (common_iterator::_M_assign): New function implementing assignment. (common_iterator::operator=): Use _M_assign. (common_iterator::_S_valueless): New constant. * testsuite/24_iterators/common_iterator/100823.cc: New test. (cherry picked from commit 56c999860bbbb2fd5091ba0985e2e5eaa90c6478) --- diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h index ca15fb46cf2e..15fedc32d5ff 100644 --- a/libstdc++-v3/include/bits/stl_iterator.h +++ b/libstdc++-v3/include/bits/stl_iterator.h @@ -1753,6 +1753,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION noexcept(_S_noexcept()) : _M_valueless(), _M_index(__x._M_index) { + __glibcxx_assert(__x._M_has_value()); if (_M_index == 0) { if constexpr (is_trivially_default_constructible_v<_It>) @@ -1790,14 +1791,58 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } } + constexpr + common_iterator(common_iterator&& __x) + noexcept(_S_noexcept<_It, _Sent>()) + : _M_valueless(), _M_index(__x._M_index) + { + if (_M_index == 0) + { + if constexpr (is_trivially_default_constructible_v<_It>) + _M_it = std::move(__x._M_it); + else + ::new((void*)std::__addressof(_M_it)) _It(std::move(__x._M_it)); + } + else if (_M_index == 1) + { + if constexpr (is_trivially_default_constructible_v<_Sent>) + _M_sent = std::move(__x._M_sent); + else + ::new((void*)std::__addressof(_M_sent)) + _Sent(std::move(__x._M_sent)); + } + } + + constexpr common_iterator& + operator=(const common_iterator&) = default; + common_iterator& operator=(const common_iterator& __x) noexcept(is_nothrow_copy_assignable_v<_It> && is_nothrow_copy_assignable_v<_Sent> && is_nothrow_copy_constructible_v<_It> && is_nothrow_copy_constructible_v<_Sent>) + requires (!is_trivially_copy_assignable_v<_It> + || !is_trivially_copy_assignable_v<_Sent>) + { + _M_assign(__x); + return *this; + } + + constexpr common_iterator& + operator=(common_iterator&&) = default; + + common_iterator& + operator=(common_iterator&& __x) + noexcept(is_nothrow_move_assignable_v<_It> + && is_nothrow_move_assignable_v<_Sent> + && is_nothrow_move_constructible_v<_It> + && is_nothrow_move_constructible_v<_Sent>) + requires (!is_trivially_move_assignable_v<_It> + || !is_trivially_move_assignable_v<_Sent>) { - return this->operator=<_It, _Sent>(__x); + _M_assign(std::move(__x)); + return *this; } template @@ -1812,48 +1857,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION && is_nothrow_assignable_v<_It&, const _It2&> && is_nothrow_assignable_v<_Sent&, const _Sent2&>) { - switch(_M_index << 2 | __x._M_index) - { - case 0b0000: - _M_it = __x._M_it; - break; - case 0b0101: - _M_sent = __x._M_sent; - break; - case 0b0001: - _M_it.~_It(); - _M_index = -1; - [[fallthrough]]; - case 0b1001: - ::new((void*)std::__addressof(_M_sent)) _Sent(__x._M_sent); - _M_index = 1; - break; - case 0b0100: - _M_sent.~_Sent(); - _M_index = -1; - [[fallthrough]]; - case 0b1000: - ::new((void*)std::__addressof(_M_it)) _It(__x._M_it); - _M_index = 0; - break; - default: - __glibcxx_assert(__x._M_has_value()); - __builtin_unreachable(); - } + __glibcxx_assert(__x._M_has_value()); + _M_assign(__x); return *this; } ~common_iterator() { - switch (_M_index) - { - case 0: - _M_it.~_It(); - break; - case 1: - _M_sent.~_Sent(); - break; - } + if (_M_index == 0) + _M_it.~_It(); + else if (_M_index == 1) + _M_sent.~_Sent(); } decltype(auto) @@ -2007,7 +2021,37 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION requires (!same_as<_It2, _Sent2>) && copyable<_It2> friend class common_iterator; - bool _M_has_value() const noexcept { return _M_index < 2; } + bool + _M_has_value() const noexcept { return _M_index != _S_valueless; } + + template + void + _M_assign(_CIt&& __x) + { + if (_M_index == __x._M_index) + { + if (_M_index == 0) + _M_it = std::forward<_CIt>(__x)._M_it; + else if (_M_index == 1) + _M_sent = std::forward<_CIt>(__x)._M_sent; + } + else + { + if (_M_index == 0) + _M_it.~_It(); + else if (_M_index == 1) + _M_sent.~_Sent(); + _M_index = _S_valueless; + + if (__x._M_index == 0) + ::new((void*)std::__addressof(_M_it)) + _It(std::forward<_CIt>(__x)._M_it); + else if (__x._M_index == 1) + ::new((void*)std::__addressof(_M_sent)) + _Sent(std::forward<_CIt>(__x)._M_sent); + _M_index = __x._M_index; + } + } union { @@ -2015,7 +2059,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _Sent _M_sent; unsigned char _M_valueless; }; - unsigned char _M_index; // 0==_M_it, 1==_M_sent, 2==valueless + unsigned char _M_index; // 0 == _M_it, 1 == _M_sent, 2 == valueless + + static constexpr unsigned char _S_valueless{2}; }; template diff --git a/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc b/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc new file mode 100644 index 000000000000..4f2b23de8cc5 --- /dev/null +++ b/libstdc++-v3/testsuite/24_iterators/common_iterator/100823.cc @@ -0,0 +1,43 @@ +// { dg-options "-std=gnu++20 -D_GLIBCXX_ASSERTIONS" } +// { dg-do run { target c++20 } } +#include +#include +#include + +void +test_valueless_assignment() +{ + int x[1] { }; + __gnu_test::test_forward_range r(x); + using Iter = decltype(r.begin()); + using Sent = decltype(r.end()); + + std::common_iterator i; + const std::common_iterator j(r.begin()); + try + { + struct Bomb + { + bool operator==(Iter) const { return true; } + operator Sent() const { throw 1; } + }; + std::common_iterator b{Bomb{}}; + i = b; // Throws, leaving i valueless-by-exception. + VERIFY(false); + } + catch (int) + { + std::common_iterator k(i); + + // PR libstdc++/100823 + k = i; // Valid even though both operands are valueless. + + i = j; // No longer valueless. + } + VERIFY( i == j ); +} + +int main() +{ + test_valueless_assignment(); +}