>
> But we're using it in indirect_ref_may_alias_decl_p as
>
> /* If second reference is view-converted, give up now. */
> if (same_type_for_tbaa (TREE_TYPE (dbase2), TREE_TYPE (ptrtype2)) !=
> 1)
> return true;
>
> and clearly if TREE_TYPE (ptrtype2) is void * while TREE_TYPE (dbase2)
> is T * we've "view-converted" things.
>
> Not sure what the consequence is when we fall through here since those
> checks may be redundant now(?) But given we're late for GCC 10 I'd
> rather be safe than sorry ;)
I think this check is about part of access path missing (i.e. we have
access path like a.b.c.d.e.f while mem-ref took part of it away
so we have a.b.c...f).
So here c and f should not be both pointers.
>
> > For ICF checking we need to be more careful anyway (in particular we do
> > not want all those -1s on arrays), so I would worry about that next
> > stage1.
> >
> > With 1 we will probably save some work since the code will not continue
> > looking for must aliases.
>
> I think we have still quite some cleanup to do for the path-based
> disambiguations.
Yep, one issue at a time....
Honza
>
> Richard.
>
> > Honza
> >
> > >
> > > So, like the following.
> > >
> > > Richard.
> > >
> > >
> > > middle-end/94539 - void * aliases every other pointer
> > >
> > > This makes same_type_for_tbaa_p conservative in the same way
> > > get_alias_set is about void * which we allow to alias all other
> > > pointers.
> > >
> > > 2020-04-14 Richard Biener <rguent...@suse.de>
> > >
> > > PR middle-end/94539
> > > * tree-ssa-alias.c (same_type_for_tbaa): Defer to
> > > alias_sets_conflict_p for pointers.
> > >
> > > * gcc.dg/alias-14.c: Make dg-do run.
> > > ---
> > > gcc/testsuite/gcc.dg/alias-14.c | 2 +-
> > > gcc/tree-ssa-alias.c | 11 ++++++++++-
> > > 2 files changed, 11 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/gcc/testsuite/gcc.dg/alias-14.c
> > > b/gcc/testsuite/gcc.dg/alias-14.c
> > > index 1ca1c09d5e3..24f0d1c1168 100644
> > > --- a/gcc/testsuite/gcc.dg/alias-14.c
> > > +++ b/gcc/testsuite/gcc.dg/alias-14.c
> > > @@ -1,4 +1,4 @@
> > > -/* { dg-do compile } */
> > > +/* { dg-do run } */
> > > /* { dg-options "-O2" } */
> > > #include <stddef.h>
> > > void *a;
> > > diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
> > > index df9ba0de0d6..ede4f198342 100644
> > > --- a/gcc/tree-ssa-alias.c
> > > +++ b/gcc/tree-ssa-alias.c
> > > @@ -839,7 +839,16 @@ same_type_for_tbaa (tree type1, tree type2)
> > > would mean that conversions between them are useless, whereas they
> > > are
> > > not (e.g. type and subtypes can have different modes). So, in the
> > > end,
> > > they are only guaranteed to have the same alias set. */
> > > - if (get_alias_set (type1) == get_alias_set (type2))
> > > + alias_set_type set1 = get_alias_set (type1);
> > > + alias_set_type set2 = get_alias_set (type2);
> > > + if (set1 == set2)
> > > + return -1;
> > > +
> > > + /* Pointers to void are considered compatible with all other pointers,
> > > + so for two pointers see what the alias set resolution thinks. */
> > > + if (POINTER_TYPE_P (type1)
> > > + && POINTER_TYPE_P (type2)
> > > + && alias_sets_conflict_p (set1, set2))
> > > return -1;
> > >
> > > /* The types are known to be not equal. */
> > > --
> > > 2.13.7
> > >
> >
>
> --
> Richard Biener <rguent...@suse.de>
> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
