On Wed, 25 Jul 2018, Jonathan Wakely wrote:
_M_copy_data is not really needed, we could add a defaulted assignment
operator, or remove the move constructor (and call a new _M_clear() from
the 2 users), etc. However, it seemed the least intrusive, the least likely
to have weird consequences.
Yes, the alternative would be:
--- a/libstdc++-v3/include/bits/stl_vector.h
+++ b/libstdc++-v3/include/bits/stl_vector.h
@@ -100,14 +100,17 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
: _M_start(__x._M_start), _M_finish(__x._M_finish),
_M_end_of_storage(__x._M_end_of_storage)
{ __x._M_start = __x._M_finish = __x._M_end_of_storage = pointer(); }
+
+ _Vector_impl_data(const _Vector_impl_data&) = default;
+ _Vector_impl_data& oeprator=(const _Vector_impl_data&) = default;
#endif
void
_M_swap_data(_Vector_impl_data& __x) _GLIBCXX_NOEXCEPT
{
- std::swap(_M_start, __x._M_start);
- std::swap(_M_finish, __x._M_finish);
- std::swap(_M_end_of_storage, __x._M_end_of_storage);
+ _Vector_impl_data __tmp = *this;
+ *this = __x;
+ __x = __tmp;
Or just std::swap(*this, __x).
}
};
Your _M_copy_data seems fine. It avoids unintentional copies, because
the copy constructor and copy assignment operator remain deleted (at
least in C++11).
I didn't add a testcase because I don't see any dg-final scan-tree-dump in
the libstdc++ testsuite. The closest would be g++.dg/pr83239.C,
g++.dg/vect/pr64410.cc, g++.dg/vect/pr33426-ivdep-4.cc that include
<vector>, but from previous experience (already with vector), adding
libstdc++ testcases to the C++ testsuite is not very popular.
Yes, C++ tests using std::vector are sometimes a bit fragile.
I don't see any reason we can't use scan-tree-dump in the libstdc++
testsuite, if you wanted to add one. We do have other dg-final tests.
The others only test for the presence of some name in assembly. But I may
try it later.
--
Marc Glisse
