https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100004
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
Version|unknown |11.0
Keywords| |missed-optimization
Status|UNCONFIRMED |RESOLVED
Resolution|--- |WONTFIX
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
void assign_via_pointer(Wrap1* w1, Wrap2* w2)
{
Foo* f1 = &w1->foo;
Foo* f2 = &w2->foo;
f1->x = 5;
f1->x = f2->x;
to GCC &wN->foo is just address arithmetic - GCC does not assume that at
w1 or w2 dynamic types of type Wrap1 or Wrap2 reside and thus it cannot
disambiguate f1->x and f2->x here because the actual accesses only involve
the type Foo.
In the assign_direct case the access paths contain Wrap1 and Wrap2 and thus
we _do_ assume dynamic types Wrap1 and Wrap2 are in effect and thus we can
disambiguate.
This is how GIMPLEs memory model works, there's no bug here. Maybe the
C++ language makes more strict guarantees (but I think it would run
against standard coding practices).
