------- Comment #4 from pinskia at gcc dot gnu dot org 2006-09-21 04:23 -------
may_alias_p returns true
for:
(gdb) p debug_generic_expr (ptr)
xaD.1527
(gdb) p debug_generic_expr (var)
SMT.5D.1548
(In reply to comment #2)
> So, actually, i'm pretty sure they should have the same SMT, because they
> should be in the same alias set.
They are not the exact same aliasing set but conflicting ones.
> Why do they get different SMT's?
Because of this:
/* To avoid creating unnecessary memory tags, only create one memory tag
per alias set class. Note that it may be tempting to group
memory tags based on conflicting alias sets instead of
equivalence. That would be wrong because alias sets are not
necessarily transitive (as demonstrated by the libstdc++ test
23_containers/vector/cons/4.cc). Given three alias sets A, B, C
such that conflicts (A, B) == true and conflicts (A, C) == true,
it does not necessarily follow that conflicts (B, C) == true. */
But I don't see how saying more than one thing conflicts, we get wrong code out
of it.
--
pinskia at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|[4.2 Regression] |[4.2 Regression]
|Misscompilation due to |Misscompilation with structs
|struct alias |due to new struct alias
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29156
