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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/110807] [13/14 Regression] Copy list initialisation
 of a vector<bool> raises a warning with -O2
Date: Wed, 26 Jul 2023 12:04:02 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110807

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
I think this is the same warning that causes libstdc++ testsuite failures w=
hen
testing with --target_board=3Dunix/-D_GLIBCXX_DEBUG

FAIL: 23_containers/vector/bool/swap.cc (test for excess errors)

I thought I'd already reported that, but I can't find it.

The library allocates space for N elements then copies n elements:

      vector(const vector& __x)
      : _Base(_Bit_alloc_traits::_S_select_on_copy(__x._M_get_Bit_allocator=
()))
      {
        _M_initialize(__x.size());
        _M_copy_aligned(__x.begin(), __x.end(), begin());
      }

We probably have the usual problem that GCC thinks allocating memory might
alter __x because it's a global, and so in theory (but never in practice) t=
he
program could replace operator new with something insane that modifies the
global.

I tried changing the constructor to:

        const_iterator __xbegin =3D __x.begin(), __xend =3D __x.end();
        _M_initialize(__x.size());
        _M_copy_aligned(__xbegin, __xend, begin());

That fixes the library test FAILs, but not the case in this bug report.=