On Fri, Aug 23, 2019 at 9:19 PM Jeff Law <l...@redhat.com> wrote: > > On 8/22/19 4:46 AM, Richard Biener wrote: > >>> Also you seem to use this info to constrain optimization when you > >>> might remember that types of addresses do not carry such information... > >>> Thus it should be "trivially" possible to write a testcase that is > >>> miscompiled > >>> after your patch. I also don't see this really exercised in the > >>> testcases you add? > >> Arggh. You're absolutely correct. I must be blocking out that entire > >> discussion from last summer due to the trama :-) > >> > >> If the destination is the address of a _DECL node, can we use the size > >> of the _DECL? > > > > Yes, but this should already happen for both invariant ones like &a.b.c > > and variant ones like &a.b[i].c in ao_ref_init_from_ptr_and_size. > I don't see that in ao_ref_init_from_ptr_and_size. AFAICT if you don't > know the size when you call that routine (size == NULL), then you end up > with the ref->size and ref->max_size set to -1. > > Am I missing something here?
Ah, of course. ao_ref_from_ptr_and_size would need to be extended to constrain max_size. So what I was saying is that ao_ref_init_from_ptr_and_size should get you a DECL ao_ref_base () from which you could constrain max_size with. Or rather ao_ref_from_ptr_and_size should be extended do that, mimicing what get_ref_base_and_extent does at the end in the if (DECL_P (exp)) case (mind flag_unconstrained_commons!). Richard. > > Jeff
