https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117912
--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
>From what I can see, this VN is purely from vn_reference_eq and it just skips
over
the COMPONENT_REFs after taking into account their vro?->off (but I do not yet
understand why the similar case with unions isn't handled the same).
So if we want to disallow value numbering them the same before PROP_objsz in
problematic cases which lead to same offset through different access path, we'd
need to do it somewhere before for (; vr1->operands.iterate (i, &vro1); i++).
And the problematic cases for objsz are either zero sized FIELD_DECLs (one of
them but not both), or I guess as well starting offset of one field vs. ending
offset of another field, say if we have
struct S { char a[24]; char b[24]; char c; };
and struct S *p, then &p->a[24] might value number the same as &p->b[0] or vice
versa, but __builtin_object_size (, 1) in one case should be 0 and in the other
case should be 24 (minimum with actual object size).
