Make nonoverlapping_component_refs work with duplicated main variants

[Richard Biener]

On Tue, 9 Jul 2019, Jan Hubicka wrote:

> > > tree_int_cst_equal will return false if offsets are not INTEGER_CST.
> > > I was not sure if I can safely use operand_equal_p.  What happens for
> > > fields with variable offsets when I inline two copies of same function
> > > which takes size as parameter and make the size different? Will I get
> > > here proper SSA name so operand_equal_p will work?
> > 
> > No, you get a DECL, but yes, I think operand_equal_p will work.
> > Consider two _same_ variable sizes, you'll not see that you
> > have to return zero then?  But yes, in case you have types
> > globbed to the canonical type (but not FIELD_DECLs) then
> > you'll get false !operand_equal_p as well.
> > 
> > The question is really what is desired here.  If you want/need precision
> > for non-constant offsets then you have to look at the COMPONENT_REF
> > trees because the relevant offset (SSA name) is only there
> > (in TREE_OPERAND (component_ref, 2)).
> > 
> > If you want to give up for non-constants and can do that without
> > correctness issue then fine (but Ada probably would like to have
> > it - so also never forget to include Ada in testing here ;))
> 
> I would like to have precision here. so perhaps as incremental change I
> can
>  1) reorganize callers to pass refs rather than just field_decls
>  2) check if TREE_OPERAND (component_ref, 2) is non-NULL in both case
>     a) if so do operand_equal_p on them and return 0 on match
>     b) if there is no match see if I have same canonical types and
>        return 1 then
>     c) return -1 otherwise

makes sense

>  3) continue with parsing FIELD_DECLS we work on now.
> > 
> > Oh, OK ... a bit more explaining commentary might be nice
> > (at the top of the function - basically what the input
> > constraints to the FIELD_DECLs are).
> 
> OK, will try to improve comments (though i tried to be relatively
> thorough).
> 
> Honza
> > 
> > Btw, the offsets in FIELD_DECLs are relative to DECL_CONTEXT so
> > comparing when DECL_CONTEXT are not related at all doesn't make
> > any sense.  Well, unless we know _those_ are at the same offset,
> > so - the constraint for the FIELD_DECLs we compare is that
> > the containing structure type object instances live at the same
> > address?
> > 
> > Richard.
> 

-- 
Richard Biener <rguenther@suse.de>
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