Re: Add access through parameter derference tracking to modref

[Jan Hubicka <hubicka@ucw.cz>]

> > +  else if (TREE_CODE (op) == SSA_NAME
> > +          && POINTER_TYPE_P (TREE_TYPE (op)))
> > +    {
> > +      if (DECL_P (base) && !ptr_deref_may_alias_decl_p (op, base))
> > +       return false;
> > +      if (TREE_CODE (base) == SSA_NAME
> > +         && !ptr_derefs_may_alias_p (op, base))
> > +       return false;
> > +    }
> 
> this all looks redundant - why is it important to look at the
> base of ref, why not simply ask below (*)
> 
> > +         modref_access_node *access_node;
> > +         FOR_EACH_VEC_SAFE_ELT (ref_node->accesses, k, access_node)
> > +           {
> > +             if (num_tests >= max_tests)
> > +               return true;
> > +
> > +             if (access_node->parm_index == -1
> > +                 || (unsigned)access_node->parm_index
> > +                    >= gimple_call_num_args (stmt))
> > +               return true;
> > +
> > +             tree op = gimple_call_arg (stmt, access_node->parm_index);
> > +
> > +             alias_stats.modref_baseptr_tests++;
> > +
> > +             /* Lookup base, if this is the first time we compare bases.  */
> > +             if (!base)
> 
> Meh, so this function is a bit confusing with base_node, ref_node,
> access_node and now 'base' and 'op'.  The loop now got a
> new nest as well.
> 
> I'm looking for a high-level description of the modref_tree <>
> but cannot find any which makes reviewing this quite difficult...

There is a description in ipa-modref.c though it may need a bit of expanding.
Basically the modref summary represents a decision tree for
tree-ssa-alias that has three levels
  1) base which records base alias set,
  2) ref which records ref alias set and
  3) access wich presently records info whether the access is a
  dreference of pointer passed by parameter. In future I will re-add
  info about offset/size and base type. It would be posisble to record
  the access path though I am not sure if that it is worth the effort
> 
> > +               {
> > +                 base = ref->ref;
> > +                 while (handled_component_p (base))
> > +                   base = TREE_OPERAND (base, 0);
> 
> ao_ref_base (ref)?  OK, that might strip an inner
> MEM_REF, yielding in a decl, but ...
> 
> > +                 if (TREE_CODE (base) == MEM_REF
> > +                     || TREE_CODE (base) == TARGET_MEM_REF)
> > +                   base = TREE_OPERAND (base, 0);
> 
> that might happen here, too.  But in the MEM_REF case base
> is a pointer.
> 
> > +               }
> > +
> > +             if (base_may_alias_with_dereference_p (base, op))
> 
> So this is a query purely at the caller side - whether 'ref' may
> alias 'op'.
> 
> ---
> 
> (*) ptr_deref_may_alias_ref_p_1 (op, ref)
> 
> without any of the magic?

Hmm, it may actually just work, I did not know that looks through
memrefs, let me re-test the patch.
> 
> Can you please amend ipa-modref-tree.h/c with a toplevel comment
> layint out the data structure and what is recorded?

I will do (but need to think bit of a redundancy between comment in
ipa-modref and ipa-modref-tree)

Honza
> 
> Thanks,
> Richard.
> 
> > +               return true;
> > +             num_tests++;
> > +           }
> >         }
> >      }
> >    return false;
> > @@ -2510,7 +2584,7 @@ ref_maybe_used_by_call_p_1 (gcall *call, ao_ref *ref, bool tbaa_p)
> >           modref_summary *summary = get_modref_function_summary (node);
> >           if (summary)
> >             {
> > -             if (!modref_may_conflict (summary->loads, ref, tbaa_p))
> > +             if (!modref_may_conflict (call, summary->loads, ref, tbaa_p))
> >                 {
> >                   alias_stats.modref_use_no_alias++;
> >                   if (dump_file && (dump_flags & TDF_DETAILS))
> > @@ -2934,7 +3008,7 @@ call_may_clobber_ref_p_1 (gcall *call, ao_ref *ref, bool tbaa_p)
> >           modref_summary *summary = get_modref_function_summary (node);
> >           if (summary)
> >             {
> > -             if (!modref_may_conflict (summary->stores, ref, tbaa_p))
> > +             if (!modref_may_conflict (call, summary->stores, ref, tbaa_p))
> >                 {
> >                   alias_stats.modref_clobber_no_alias++;
> >                   if (dump_file && (dump_flags & TDF_DETAILS))