On Wed, Apr 8, 2009 at 5:42 PM, Ian Lance Taylor <i...@google.com> wrote: > John Engelhart <john.engelh...@gmail.com> writes: > >> Objective-C defines 'c_common_get_alias_set' as its language specific >> alias set manager. c_common_get_alias_set() seems(?) to only >> implement C's strict aliasing rules, with no provisions for >> Objective-C's needs. > >> Can anyone with a much better understanding of GCC's internals comment on >> this? > > I think you are correct about what is happening today. > > Since I don't know anything about Objective C, I don't know what should > happen instead. I would guess that you would want to set up a tree of > alias sets, using record_alias_subset.
The 'right thing' is pretty tricky. I've given it some thought and I can't come up with a simple set of rules that cleanly mesh with C99's rules. I think that coming up with a 'right answer' would take an awful lot of very carefully considered thought. The easiest, and I think safest, course of action would be to add a line in c_common_get_alias_set similar to the one I suggested. That is, if it is a pointer to something that looks even remotely like an objective-c "object", then just assume that it can alias anything. Any recommendations on what to do next? Filing a bug seems like the step, I just wanted to see if I had missed something in my analysis of the problem.
