[Bug sanitizer/80797] -fsanitize=null doesn't instrument &s->x

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80797

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
We don't instrument such expressions because
v_3 = &s_2->i;
is not gimple_assign_load_p:

1997           if (flag_sanitize & (SANITIZE_NULL | SANITIZE_ALIGNMENT))
1998             {
1999               if (gimple_store_p (stmt))
2000                 instrument_null (gsi, true);
2001               if (gimple_assign_load_p (stmt))
2002                 instrument_null (gsi, false);
2003             }

So I think we could use gimple_assign_single_p instead of gimple_assign_load_p
and then strip the ADDR_EXPR in instrument_null before getting its base
address.  Untested.