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

[jason at gcc dot gnu.org]

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

--- Comment #18 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Jason Merrill from comment #17)
> There's probably a way to help the optimizer out without the
> __builtin_unreachable hammer, as for 98465; suggestions are welcome.

..like https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104336#c1