[Bug c++/109514] New: [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[Bug c++/109514] New: [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109514

            Bug ID: 109514
           Summary: [13 regression] -Werror=dangling-pointer false
                    positive nn fheroes-1.0.3 (lambdas)
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: slyfox at gcc dot gnu.org
  Target Milestone: ---

Initially noticed the false positive on fheroes2-1.0.3 project which uses
-Werror by default. Here is the extracted example:

// $ cat screen.cpp
#include <set>
#include <vector>

struct R {
    int w;
};

typedef std::vector<R> vr_t;
typedef std::set<R> sr_t;

static sr_t FilterRs (const sr_t & rs)
{
    return rs;
}

vr_t getRs ()
{
    const vr_t filteredRs = []() {
        sr_t rs;

        rs = FilterRs (rs);

        return vr_t{rs.begin(), rs.end()};
    }();

    return filteredRs;
}

$ g++ -c -O2 screen.cpp -Werror=dangling-pointer
In file included from /<<NIX>>/gcc-13.0.0/include/c++/13.0.1/set:62,
                 from screen.cpp:1:
In member function 'void
std::_Rb_tree_header::_M_move_data(std::_Rb_tree_header&)',
    inlined from 'void std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_move_data(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>&, std::true_type) [with _Key = R; _Val = R; _KeyOfValue =
std::_Identity<R>; _Compare = std::less<R>; _Alloc = std::allocator<R>]' at
/<<NIX>>/gcc-13.0.0/include/c++/13.0.1/bits/stl_tree.h:1421:29,
    inlined from 'void std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::_M_move_assign(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>&, std::true_type) [with _Key = R; _Val = R; _KeyOfValue =
std::_Identity<R>; _Compare = std::less<R>; _Alloc = std::allocator<R>]' at
/<<NIX>>/gcc-13.0.0/include/c++/13.0.1/bits/stl_tree.h:1710:14,
    inlined from 'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&
std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare,
_Alloc>::operator=(std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&&)
[with _Key = R; _Val = R; _KeyOfValue = std::_Identity<R>; _Compare =
std::less<R>; _Alloc = std::allocator<R>]' at
/<<NIX>>/gcc-13.0.0/include/c++/13.0.1/bits/stl_tree.h:1744:21,
    inlined from 'std::set<_Key, _Compare, _Alloc>& std::set<_Key, _Compare,
_Alloc>::operator=(std::set<_Key, _Compare, _Alloc>&&) [with _Key = R; _Compare
= std::less<R>; _Alloc = std::allocator<R>]' at
/<<NIX>>/gcc-13.0.0/include/c++/13.0.1/bits/stl_set.h:302:7,
    inlined from 'getRs()::<lambda()>' at screen.cpp:21:26,
    inlined from 'vr_t getRs()' at screen.cpp:24:7:
/<<NIX>>/gcc-13.0.0/include/c++/13.0.1/bits/stl_tree.h:199:38: error: storing
the address of local variable 'rs' in '*MEM[(struct _Rb_tree_node_base *
&)&D.35566 + 16].std::_Rb_tree_node_base::_M_parent'
[-Werror=dangling-pointer=]
  199 |       _M_header._M_parent->_M_parent = &_M_header;
      |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
screen.cpp: In function 'vr_t getRs()':
screen.cpp:19:14: note: 'rs' declared here
   19 |         sr_t rs;
      |              ^~
screen.cpp:19:14: note: '<unnamed>.std::set<R, std::less<R>, std::allocator<R>
>::_M_t.std::_Rb_tree<R, R, std::_Identity<R>, std::less<R>, std::allocator<R>
>::_M_impl.std::_Rb_tree<R, R, std::_Identity<R>, std::less<R>,
std::allocator<R> >::_Rb_tree_impl<std::less<R>,
true>::<unnamed>.std::_Rb_tree_header::_M_header.std::_Rb_tree_node_base::_M_parent'
declared here
cc1plus: some warnings being treated as errors

I think it's a false positive (or maybe it exposes some NRVO bug?).

$ g++ -v
Using built-in specs.
COLLECT_GCC=/<<NIX>>/gcc-13.0.0/bin/g++
COLLECT_LTO_WRAPPER=/<<NIX>>/gcc-13.0.0/libexec/gcc/x86_64-unknown-linux-gnu/13.0.1/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with:
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 13.0.1 20230409 (experimental) (GCC)

[Bug c++/109514] [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109514

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-04-14
                 CC|                            |jason at gcc dot gnu.org
           Assignee|unassigned at gcc dot gnu.org      |jason at gcc dot gnu.org
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1

--- Comment #1 from Jason Merrill <jason at gcc dot gnu.org> ---
Confirmed.  -Wdangling-pointer shouldn't warn about a store to an unknown
object.  And it should be able to figure out that this store is to sr itself,
and not warn for that reason as well.

[Bug c++/109514] [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109514

--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:9964df74a9e99e850bf9b0b6ff5c47133f846db8

commit r13-7190-g9964df74a9e99e850bf9b0b6ff5c47133f846db8
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Apr 14 13:37:16 2023 -0400

    -Wdangling-pointer: fix MEM_REF handling [PR109514]

    Here we hit the MEM_REF case, with its arg an ADDR_EXPR, but had no
handling
    for that and wrongly assumed it would be a reference to a local variable.
    This patch overhauls the logic for deciding whether the target is something
    to warn about so that we only warn if we specifically recognize the target
    as non-local.  None of the existing tests regress as a result.

            PR c++/109514

    gcc/ChangeLog:

            * gimple-ssa-warn-access.cc (pass_waccess::check_dangling_stores):
            Overhaul lhs_ref.ref analysis.

    gcc/testsuite/ChangeLog:

            * g++.dg/warn/Wdangling-pointer-6.C: New test.

[Bug c++/109514] [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109514

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |13.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #3 from Jason Merrill <jason at gcc dot gnu.org> ---
Fixed.

[Bug c++/109514] [13 regression] -Werror=dangling-pointer false positive nn fheroes-1.0.3 (lambdas)

[slyfox at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109514

--- Comment #4 from Sergei Trofimovich <slyfox at gcc dot gnu.org> ---
Thank you, Jason!

I tested the original code from fheroes2-1.0.3. It also compiles without
warnings.