https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97474
--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
OK, so the issue is that the C++ frontend marks 'this' as restrict which in
turn means that no other pointer can alias it. For foo() GCC computes
<bb 2> :
_1 = MEM[(struct A &)a_7(D) clique 1 base 1].a;
# PT = nonlocal escaped null
_2 = MEM[(struct A &)a_7(D) clique 1 base 1].b;
_3 = MEM[(int &)_2 clique 1 base 0];
_4 = _1 * _3;
MEM[(struct A &)a_7(D) clique 1 base 1].a = _4;
# PT = nonlocal escaped null
_5 = MEM[(struct A &)a_7(D) clique 1 base 1].b;
_9 = MEM[(int &)_5 clique 1 base 0];
return _9;
in particular
a_7(D), points-to NULL, points-to vars: { D.2410 } (nonlocal, restrict)
_5, points-to non-local, points-to escaped, points-to NULL, points-to vars: { }
and thus the load of _9 via _5 does not alias the store via a_7. Basically,
GCC does not consider storage pointed to by a restrict pointer to point to
itself (what the CTOR does - make b refer to its own a).
It's not difficult to fix this - simply amend the constraints:
a = &PARM_NOALIAS(9)
PARM_NOALIAS(9) = &NONLOCAL
also have
PARM_NOALIAS(9) = &PARM_NOALIAS(9)
the question is whether this generally applies to restrict qualified pointers.
In some sense for
A * restrict p;
int *q = p->b;
q is derived from p.
