> > OK, so the explanation is not as simple as claim that non-POD types > > needs to be constructed or copied by constructor and C++ FE always > > generate an explicit vtbl store? > > No as optimizers may combine stores for example.
Yep, I understand we can design "evil" optimization that will make problem of tracking virtual table pointers very hard. The question is how much we want to have these pre-IPA and how their benefits relate to beenfits from improved devirtualization. We are still weak on deivrt (and current generation benchmarks don't seem to care much on how good we are), so at the moment my approach is to improve the analysis without imposing additional restriction. but in longer turn we may want to make some compromises (pre-ipa) here and preserve more information in gimple. Honza > > >> Of course, having gimple defined and required annotation for vptr > >> changes would be much better but then of course all transformations > >> would have to make sure they preserve it. > >> > >> IIRC, flag_strict_aliasing test was explicitely Richard's request, > >> perhaps we could restrict the pointer type test further. > >> > >> Does that answer your question? > > > > Sort of, yes. We should make some analysis how effective current > > methods are (i.e. disabling it and checking how much devirtualization > > improve for firefox) and if we find they seem insufficient, we probably > > should think of better analysis or annotation... > > > > Honza
