[Bug c++/114945] New: Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning with gcc 14

[Bug c++/114945] New: Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning with gcc 14

[nilsgladitz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114945

            Bug ID: 114945
           Summary: Sporadic std::vector::resize() -Wstringop-overflow or
                    -Warray-bounds warning with gcc 14
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: nilsgladitz at gmail dot com
  Target Milestone: ---

Created attachment 58103
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58103&action=edit
Testcase

Initially seen with a Ubuntu specific GCC 14 x86-64 snapshot but also
reproduced with a vanilla arm32 build of GCC 14.1-rc1. Not seen with GCC 13.1.

I see there are a couple of issues which sound similar or related (e.g. bugs
113664, 106185, 105823, 105746) but I can't really tell if this is a duplicate
or regression of a previously fixed issue.

The reduced attached test case compiled with
    g++-14 -std=c++20 -O2 case1.cpp

Produces the warning:
/usr/include/c++/14/bits/stl_algobase.h:972:25: warning: ‘void*
__builtin_memset(void*, int, long unsigned int)’ writing 3 bytes into a region
of size 0 overflows the destination [-Wstringop-overflow=]
  972 |         __builtin_memset(__first, static_cast<unsigned char>(__tmp),
__len);
      |        
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Adding -Wall replaces the above warning with this new warning:
/usr/include/c++/14/bits/stl_algobase.h:972:25: warning: ‘void*
__builtin_memset(void*, int, long unsigned int)’ offset [0, 2] is out of the
bounds [0, 0] [-Warray-bounds=]
  972 |         __builtin_memset(__first, static_cast<unsigned char>(__tmp),
__len);
      |        
~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Also recreated this on godbolt: https://godbolt.org/z/rYx9q7Ke1

[Bug tree-optimization/114945] [14/15 regression] Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning with gcc 14

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114945

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[14 regression] Sporadic    |[14/15 regression] Sporadic
                   |std::vector::resize()       |std::vector::resize()
                   |-Wstringop-overflow or      |-Wstringop-overflow or
                   |-Warray-bounds warning with |-Warray-bounds warning with
                   |gcc 14                      |gcc 14
   Target Milestone|---                         |14.0

[Bug tree-optimization/114945] [14/15 regression] Sporadic std::vector::resize() -Wstringop-overflow or -Warray-bounds warning with gcc 14

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114945

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|14.0                        |14.2

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 14.1 is being released, retargeting bugs to GCC 14.2.