Do not give up early on access path oracle

[Richard Biener]

On June 17, 2019 6:23:03 PM GMT+02:00, Richard Sandiford <richard.sandiford@arm.com> wrote:
>Jan Hubicka <hubicka@ucw.cz> writes:
>>> >> > 
>>> >> > A more stricter test would be
>>> >> > 
>>> >> > 	if (!maybe_eq (max_size1, size1) && !maybe_eq (max_size2,
>size2))
>>> >> >           return true;
>>> >> >         /* If there's a variable access in one of the refs fall
>through
>>> >> >            to access-path based disambiguation.  */
>>> >> > 
>>> >> > where you'd need to pass down ao_ref_size in addition to
>max_size as well.
>>> >> 
>>> >> Proably || here?
>>> >
>>> > Hmm, !maybe_eq () -> ! max_size1 == size1 -> max_size != size1
>thus
>>> > I think && is correct if you want to disambiguate a[1].v2 and
>a[i].v1
>>> >
>>> > But yes, if you don't want that then || is cheaper.  Probably add
>>> > another testcase with one of the accesses with a constant index?
>>> 
>>> Might be misunderstanding, but isn't the check for a variable access
>>> !known_eq (max_size1, size1) == maybe_ne (max_size1, size1)? 
>"maybe_eq"
>>> means "could be equal in some circumstances, even if they're not
>always
>>> equal".
>>
>> Seems I am getting progressively more confused.
>
>Well, me too :-)  I didn't really understand the choice of the original
>condition above.  It seemed to be "return true if both access sizes are
>variable", but the comment implied something else.

Sorry,! Must_eq is obviously fine. 

>But I was just picking up on the choice of maybe_eq vs. known_eq in the
>condition, which as things stand would only matter for SVE.  And...
>
>> I think I want to pass the size down from ao_ref to the functions and
>> then see if they are always equal.
>
>...right, that's what I mean.  known_eq gives you "always equal",
>i.e. "not variable".  The maybe_eq in the original condition seemed odd
>because it includes the constant case and (potentially) variable cases
>that are size1 or bigger.
>
>In inverted conditions, !known_eq can be written maybe_ne (but doesn't
>need to be, if !known_eq seems clearer).
>
>Thanks,
>Richard
>
>>
>> Why would I want to use maybe variant?
>>
>> Honza
>>
>>> 
>>> Richard