[Bug tree-optimization/105651] [12/13 Regression] bogus "may overlap" memcpy warning with std::string and operator+ at -O3

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105651

--- Comment #15 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note on trunk we get things way less optimized and end up with

  <bb 32> [local count: 695302893]:
  __x.38_144 = (long unsigned int) " ";
  __y.39_145 = (long unsigned int) _137;
  if (__x.38_144 < __y.39_145)
    goto <bb 34>; [50.00%]
  else
    goto <bb 33>; [50.00%]

  <bb 33> [local count: 347651447]:
  _146 = _137 + _128;
  __x.38_147 = (long unsigned int) _146;
  if (__x.38_147 < __x.38_144)
    goto <bb 34>; [50.00%]
  else
    goto <bb 39>; [50.00%]

and ptr_derefs_may_alias_p doesn't work there because to relate _137 and " "
points-to info would need to track STRING_CSTs but it
doesn't do that (we simply drop knowledge here, see find_what_var_points_to
string_id handling).