[Bug middle-end/104965] [11/12 Regression] Yet another -Warray-bounds false positive

["msebor at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104965

Martin Sebor <msebor at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |msebor at gcc dot gnu.org

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
It looks like an escape analysis limitation.  With this simpler test case using
different types to rule out aliasing assumptions:

#include <string>

int main()
{
  std::basic_string<short> s;
  auto p = new int[s.size ()]{ };
  char c = 0;
  if (s.size())
    c = *p;
  delete[] p;
  return c;
}

pr104965.C:9:9: warning: array subscript 0 is outside array bounds of ‘void
[0]’ [-Warray-bounds]
    9 |     c = *p;
      |         ^~
pr104965.C:6:34: note: object of size 0 allocated by ‘operator new []’
    6 |   auto p = new short[s.size ()]{ };
      |                                  ^

One of the stores to the local s escapes its address which is then assumed to
have been clobbered by operator new:

  <bb 2> [local count: 1073741824]:
  s ={v} {CLOBBER};
  MEM[(struct _Alloc_hider *)&s] ={v} {CLOBBER};
  MEM[(struct _Alloc_hider *)&s]._M_p = &s.D.33279._M_local_buf;
  s._M_string_length = 0;
  MEM[(char_type &)&s + 16] = 0;
  _5 = operator new [] (0);

  <bb 3> [local count: 1073741824]:
  _10 = s._M_string_length;
  if (_10 != 0)
    goto <bb 4>; [50.00%]
  else
    goto <bb 5>; [50.00%]

  <bb 4> [local count: 536870913]:
  _1 = MEM[(int *)_5];
  c_6 = (char) _1;