[Bug middle-end/88780] [12/13/14/15 Regression] bogus -Wstringop-truncation for copying as many bytes from a string as its length

[law at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88780

--- Comment #16 from Jeffrey A. Law <law at gcc dot gnu.org> ---
Some thoughts.

The block with the key statements looks like:

<bb 4> :
__builtin_strncpy (d_8(D), s_5(D), len_6);
_2 = d_8(D) + len_6;
*_2 = 0;


We probably need to recover the array indexing and produce the equivalent of
<bb 4> :
__builtin_strncpy (d_8(D), s_5(D), len_6);
d[len_6] = 0;


Then we probably need to factor the hack that looks past the strncpy so that it
works in maybe_diag_stxncpy_trunc.

Probably not gcc-15 material, but that's a path forward.