On Wed, 2 Dec 2015, Jan Hubicka wrote:
> Hi,
> this patch makes the type system to be unchanged by flag_strict_aliasing.
> This is needed to prevent optimization loss in flag_strict_aliasing code where
> some !flag_strict_aliasing code put alias set 0 into a type (this happens
> in all cases I modified in my original patch). It is also necessary to
> validate
> ipa-icf and operand_equal_p transformations to be safe for code transitions
> !flag_strict_aliasing->flag_strict_aliasing that I wasn to do in the inliner.
>
> This patch goes the opposite way than my previous attempt (and is short unlike
> the explanation ;). Instead of adding extra parameter to get_alias_set it
> makes get_alias_set do ignore flag_strict_aliasing. To make sure that no TBAA
> is used when !flag_strict_aliasing I can simply disable alias_set_subset_of
> and
> alias_sets_conflict_p which are the only way TBAA oracle can disambiguate
> items.
>
> Next there are cases where optimizations are disabled to keep TBAA right.
> I audited the code and found only function.c (that uses object_must_conflict
> for packing) and ipa-icf/fold-const. This patch updates
> objects_must_conflict_p, fold-const
> already check flag_strict_aliasing and I did not update ipa-icf because I
> would
> have to disable non-strict-aliasing path in the followup patch.
>
> I checked that there is no code difference with -fno-strict-aliasing
> -fno-ipa-icf
> with this patch on tramp3d and dealII
>
>
> Bootstrapped/regtested x86_64-linux and also lto-bootstraped. Looks OK?
>
> * alias.c (alias_set_subset_of, alias_sets_conflict_p,
> objects_must_conflict_p): Short circuit for !flag_strict_aliasing
> (get_alias_set): Remove flag_strict_aliasing check.
> (new_alias_set): Likewise.
> Index: alias.c
> ===================================================================
> --- alias.c (revision 231081)
> +++ alias.c (working copy)
> @@ -405,6 +405,10 @@ alias_set_subset_of (alias_set_type set1
> {
> alias_set_entry *ase2;
>
> + /* Disable TBAA oracle with !flag_strict_aliasing. */
> + if (!flag_strict_aliasing)
> + return true;
> +
> /* Everything is a subset of the "aliases everything" set. */
> if (set2 == 0)
> return true;
> @@ -466,6 +470,10 @@ alias_sets_conflict_p (alias_set_type se
> alias_set_entry *ase1;
> alias_set_entry *ase2;
>
> + /* Disable TBAA oracle with !flag_strict_aliasing. */
> + if (!flag_strict_aliasing)
> + return true;
> +
> /* The easy case. */
> if (alias_sets_must_conflict_p (set1, set2))
> return 1;
> @@ -561,6 +569,9 @@ objects_must_conflict_p (tree t1, tree t
> {
> alias_set_type set1, set2;
>
> + if (!flag_strict_aliasing)
> + return 1;
> +
Rather than adjusting this function please adjust
alias_sets_must_conflict_p.
Otherwise this looks ok and indeed much nicer.
Thanks,
Richard.
> /* If neither has a type specified, we don't know if they'll conflict
> because we may be using them to store objects of various types, for
> example the argument and local variables areas of inlined functions. */
> @@ -816,10 +827,12 @@ get_alias_set (tree t)
> {
> alias_set_type set;
>
> - /* If we're not doing any alias analysis, just assume everything
> - aliases everything else. Also return 0 if this or its type is
> - an error. */
> - if (! flag_strict_aliasing || t == error_mark_node
> + /* We can not give up with -fno-strict-aliasing because we need to build
> + proper type representation for possible functions which are build with
> + -fstirct-aliasing. */
> +
> + /* return 0 if this or its type is an error. */
> + if (t == error_mark_node
> || (! TYPE_P (t)
> && (TREE_TYPE (t) == 0 || TREE_TYPE (t) == error_mark_node)))
> return 0;
> @@ -1085,15 +1098,10 @@ get_alias_set (tree t)
> alias_set_type
> new_alias_set (void)
> {
> - if (flag_strict_aliasing)
> - {
> - if (alias_sets == 0)
> - vec_safe_push (alias_sets, (alias_set_entry *) NULL);
> - vec_safe_push (alias_sets, (alias_set_entry *) NULL);
> - return alias_sets->length () - 1;
> - }
> - else
> - return 0;
> + if (alias_sets == 0)
> + vec_safe_push (alias_sets, (alias_set_entry *) NULL);
> + vec_safe_push (alias_sets, (alias_set_entry *) NULL);
> + return alias_sets->length () - 1;
> }
>
> /* Indicate that things in SUBSET can alias things in SUPERSET, but that
