On 8/26/19 3:00 AM, Richard Biener wrote: > 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!). Not a bad idea to constrain ao_ref's max_size this way. Not offhand sure if other passes would be able to exploit having that max_size set, but DSE certainly could.
I'll see if I can add that and drop the equivalent DSE bits. Jeff
