On Sun, 19 May 2019, Jan Hubicka wrote:
> > On Fri, 17 May 2019, Jan Hubicka wrote:
> >
> > > Hi,
> > > this patch cuts walks in aliasing_component_refs_p if the type we look for
> > > can not fit into a given type by comparing their sizes. Similar logic
> > > already exists in indirect_ref_may_alias_decl_p.
> > >
> > > When we walk reference a.b.c.d.e looking for type x we only need to do
> > > it if sizeof(a)>=sizeof(x) and continue woking from e until
> > > sizeof(e)<=sizeof(x). We do not need to compare types where sizes are
> > > known to be different.
> > >
> > > This saves some work (by not walking refs and not comparing their types
> > > if they can not match) but also increases number of disambiguations
> > > quite noticably. This is because same_type_for_tbaa often returns -1 and
> > > makes aliasing_compinent_refs_p to give up. Using the simple size check
> > > prevents hitting such problematic type pairs in many common cases.
> > >
> > > Stats on tramp3d lto build change From:
> > >
> > > Alias oracle query stats:
> > > refs_may_alias_p: 0 disambiguations, 0 queries
> > > ref_maybe_used_by_call_p: 6451 disambiguations, 25578 queries
> > > call_may_clobber_ref_p: 817 disambiguations, 817 queries
> > > aliasing_component_ref_p: 14 disambiguations, 12528 queries
> > > TBAA oracle: 1468347 disambiguations 3010562 queries
> > > 550690 are in alias set 0
> > > 614235 queries asked about the same object
> > > 0 queries asked about the same alias set
> > > 0 access volatile
> > > 260937 are dependent in the DAG
> > > 116353 are aritificially in conflict with void *
> > >
> > > to:
> > >
> > > Alias oracle query stats:
> > > refs_may_alias_p: 0 disambiguations, 0 queries
> > > ref_maybe_used_by_call_p: 6451 disambiguations, 25580 queries
> > > call_may_clobber_ref_p: 817 disambiguations, 817 queries
> > > aliasing_component_ref_p: 118 disambiguations, 12552 queries
> > > TBAA oracle: 1468413 disambiguations 3010714 queries
> > > 550719 are in alias set 0
> > > 614247 queries asked about the same object
> > > 0 queries asked about the same alias set
> > > 0 access volatile
> > > 260970 are dependent in the DAG
> > > 116365 are aritificially in conflict with void *
> > >
> > > So disambiguations are up from 14 to 118 which is still quite low.
> > >
> > > A followup patch making types_same_for_tbaa to not give up for
> > > TYPE_STRUCTURAL_EQUALITY pointers and arrays improves hitrate to 2723.
> > >
> > > Bootstrapped/regtested x86_64-linux, OK?
> > >
> > > * tree-ssa-alias.c (type_big_enough_for_type_p): New function.
> > > (aliasing_component_refs_p): Use it.
> > > Index: tree-ssa-alias.c
> > > ===================================================================
> > > --- tree-ssa-alias.c (revision 271292)
> > > +++ tree-ssa-alias.c (working copy)
> > > @@ -735,6 +735,27 @@ ao_ref_init_from_ptr_and_size (ao_ref *r
> > > ref->volatile_p = false;
> > > }
> > >
> > > +/* Return true if TYPE1 may contain TYPE2 by its size. */
> > > +
> > > +static bool
> > > +type_big_enough_for_type_p (tree type1, tree type2)
> > > +{
> > > + if (!TYPE_SIZE (type1) || !TYPE_SIZE (type2))
> > > + return true;
> > > + /* Be conservative for arrays and vectors. We want to support partial
> > > + overlap on int[3] and int[3] as tested in gcc.dg/torture/alias-2.c.
> > > */
> > > + while (TREE_CODE (type2) == ARRAY_TYPE
> > > + || TREE_CODE (type2) == VECTOR_TYPE)
> > > + type2 = TREE_TYPE (type2);
> >
> > Eww ;) I guess this means same-type can never return true for
> > array or vectors?
> >
> > > + if (!poly_int_tree_p (TYPE_SIZE (type1))
> > > + || !poly_int_tree_p (TYPE_SIZE (type2)))
> > > + return true;
> >
> > Use
> >
> > poly_uint64 size1;
> > if (!poly_int_tree_p (TYPE_SIZE (type1), &size1)
> > ...
> >
> > > + if (known_lt (wi::to_poly_widest (TYPE_SIZE (type1)),
> > > + wi::to_poly_widest (TYPE_SIZE (type2))))
> >
> > and
> >
> > if (known_lt (size1, size2))
> >
> > I wonder if you can compute whether type1 fits in type2 and
> > the other way around at the same time, saving seemingly
> > redundant work since you test both ways most of the time below.
> > So sth like type_size_compare_for_fitting () returning
> > -1, 0, 1 and use zero for "don't know"?
>
> Hi,
> this patch implements the three way compare and also merges the code
> with same logic in indirect_ref_may_alias_decl_p.
> We end up doing more known_lt calls than necessary because sometimes we
> do not care about the three way outcome, but I asusme that this should
> be relatively cheap once we pass the earlier test and tree to poly_int
> conversion.
>
> Bootstrapped/regtested x86_64-linux, OK?
>
> * tree-ssa-alias.c (compare_sizes): New function.
> (sompare_type_sizes): New function
> (aliasing_component_refs_p): Use it.
> (indirect_ref_may_alias_decl_p): Likewise.
> Index: tree-ssa-alias.c
> ===================================================================
> --- tree-ssa-alias.c (revision 271379)
> +++ tree-ssa-alias.c (working copy)
> @@ -735,6 +735,48 @@ ao_ref_init_from_ptr_and_size (ao_ref *r
> ref->volatile_p = false;
> }
>
> +/* S1 and S2 are TYPE_SIZE or DECL_SIZE. Compare them:
> + Return -1 if S1 < S2
> + Return 1 if S1 > S2
> + Return 0 if equal or incoparable. */
incomparable.
OK with that fix.
Richard.
> +
> +static int
> +compare_sizes (tree s1, tree s2)
> +{
> + if (!s1 || !s2)
> + return 0;
> +
> + poly_uint64 size1 = poly_int_tree_p (s1, &size1);
> + poly_uint64 size2 = poly_int_tree_p (s2, &size2);
> +
> + if (!poly_int_tree_p (s1, &size1) || !poly_int_tree_p (s2, &size2))
> + return 0;
> + if (known_lt (size1, size2))
> + return -1;
> + if (known_lt (size2, size1))
> + return 1;
> + return 0;
> +}
> +
> +/* Compare TYPE1 and TYPE2 by its size.
> + Return -1 if size of TYPE1 < size of TYPE2
> + Return 1 if size of TYPE1 > size of TYPE2
> + Return 0 if types are of equal sizes or we can not compare them. */
> +
> +static int
> +compare_type_sizes (tree type1, tree type2)
> +{
> + /* Be conservative for arrays and vectors. We want to support partial
> + overlap on int[3] and int[3] as tested in gcc.dg/torture/alias-2.c. */
> + while (TREE_CODE (type1) == ARRAY_TYPE
> + || TREE_CODE (type1) == VECTOR_TYPE)
> + type1 = TREE_TYPE (type1);
> + while (TREE_CODE (type2) == ARRAY_TYPE
> + || TREE_CODE (type2) == VECTOR_TYPE)
> + type2 = TREE_TYPE (type2);
> + return compare_sizes (TYPE_SIZE (type1), TYPE_SIZE (type2));
> +}
> +
> /* Return 1 if TYPE1 and TYPE2 are to be considered equivalent for the
> purpose of TBAA. Return 0 if they are distinct and -1 if we cannot
> decide. */
> @@ -803,7 +845,7 @@ aliasing_component_refs_p (tree ref1,
> tree base1, base2;
> tree type1, type2;
> tree *refp;
> - int same_p, same_p2;
> + int same_p1 = 0, same_p2 = 0;
>
> /* Choose bases and base types to search for. */
> base1 = ref1;
> @@ -816,65 +858,93 @@ aliasing_component_refs_p (tree ref1,
> type2 = TREE_TYPE (base2);
>
> /* Now search for the type1 in the access path of ref2. This
> - would be a common base for doing offset based disambiguation on. */
> - refp = &ref2;
> - while (handled_component_p (*refp)
> - && same_type_for_tbaa (TREE_TYPE (*refp), type1) == 0)
> - refp = &TREE_OPERAND (*refp, 0);
> - same_p = same_type_for_tbaa (TREE_TYPE (*refp), type1);
> - if (same_p == 1)
> - {
> - poly_int64 offadj, sztmp, msztmp;
> - bool reverse;
> - get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp, &reverse);
> - offset2 -= offadj;
> - get_ref_base_and_extent (base1, &offadj, &sztmp, &msztmp, &reverse);
> - offset1 -= offadj;
> - if (ranges_maybe_overlap_p (offset1, max_size1, offset2, max_size2))
> + would be a common base for doing offset based disambiguation on.
> + This however only makes sense if type2 is big enough to hold type1. */
> + int cmp_outer = compare_type_sizes (type2, type1);
> + if (cmp_outer >= 0)
> + {
> + refp = &ref2;
> + while (true)
> {
> - ++alias_stats.aliasing_component_refs_p_may_alias;
> - return true;
> + /* We walk from inner type to the outer types. If type we see is
> + already too large to be part of type1, terminate the search. */
> + int cmp = compare_type_sizes (type1, TREE_TYPE (*refp));
> + if (cmp < 0)
> + break;
> + /* If types may be of same size, see if we can decide about their
> + equality. */
> + if (cmp >= 0)
> + {
> + same_p2 = same_type_for_tbaa (TREE_TYPE (*refp), type1);
> + if (same_p2 != 0)
> + break;
> + }
> + if (!handled_component_p (*refp))
> + break;
> + refp = &TREE_OPERAND (*refp, 0);
> }
> - else
> + if (same_p2 == 1)
> {
> - ++alias_stats.aliasing_component_refs_p_no_alias;
> - return false;
> + poly_int64 offadj, sztmp, msztmp;
> + bool reverse;
> + get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp, &reverse);
> + offset2 -= offadj;
> + get_ref_base_and_extent (base1, &offadj, &sztmp, &msztmp, &reverse);
> + offset1 -= offadj;
> + if (ranges_maybe_overlap_p (offset1, max_size1, offset2, max_size2))
> + {
> + ++alias_stats.aliasing_component_refs_p_may_alias;
> + return true;
> + }
> + else
> + {
> + ++alias_stats.aliasing_component_refs_p_no_alias;
> + return false;
> + }
> }
> }
>
> /* If we didn't find a common base, try the other way around. */
> - refp = &ref1;
> - while (handled_component_p (*refp)
> - && same_type_for_tbaa (TREE_TYPE (*refp), type2) == 0)
> - refp = &TREE_OPERAND (*refp, 0);
> - same_p2 = same_type_for_tbaa (TREE_TYPE (*refp), type2);
> - if (same_p2 == 1)
> - {
> - poly_int64 offadj, sztmp, msztmp;
> - bool reverse;
> -
> - get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp, &reverse);
> - offset1 -= offadj;
> - get_ref_base_and_extent (base2, &offadj, &sztmp, &msztmp, &reverse);
> - offset2 -= offadj;
> - if (ranges_maybe_overlap_p (offset1, max_size1, offset2, max_size2))
> + if (cmp_outer <= 0)
> + {
> + refp = &ref1;
> + while (true)
> {
> - ++alias_stats.aliasing_component_refs_p_may_alias;
> - return true;
> + int cmp = compare_type_sizes (type2, TREE_TYPE (*refp));
> + if (cmp < 0)
> + break;
> + /* If types may be of same size, see if we can decide about their
> + equality. */
> + if (cmp >= 0)
> + {
> + same_p1 = same_type_for_tbaa (TREE_TYPE (*refp), type2);
> + if (same_p1 != 0)
> + break;
> + }
> + if (!handled_component_p (*refp))
> + break;
> + refp = &TREE_OPERAND (*refp, 0);
> }
> - else
> + if (same_p1 == 1)
> {
> - ++alias_stats.aliasing_component_refs_p_no_alias;
> - return false;
> - }
> - }
> + poly_int64 offadj, sztmp, msztmp;
> + bool reverse;
>
> - /* In the remaining test we assume that there is no overlapping type
> - at all. So if we are unsure, we need to give up. */
> - if (same_p == -1 || same_p2 == -1)
> - {
> - ++alias_stats.aliasing_component_refs_p_may_alias;
> - return true;
> + get_ref_base_and_extent (*refp, &offadj, &sztmp, &msztmp, &reverse);
> + offset1 -= offadj;
> + get_ref_base_and_extent (base2, &offadj, &sztmp, &msztmp, &reverse);
> + offset2 -= offadj;
> + if (ranges_maybe_overlap_p (offset1, max_size1, offset2, max_size2))
> + {
> + ++alias_stats.aliasing_component_refs_p_may_alias;
> + return true;
> + }
> + else
> + {
> + ++alias_stats.aliasing_component_refs_p_no_alias;
> + return false;
> + }
> + }
> }
>
> /* If we have two type access paths B1.path1 and B2.path2 they may
> @@ -883,15 +953,19 @@ aliasing_component_refs_p (tree ref1,
> a part that we do not see. So we can only disambiguate now
> if there is no B2 in the tail of path1 and no B1 on the
> tail of path2. */
> - if (base1_alias_set == ref2_alias_set
> - || alias_set_subset_of (base1_alias_set, ref2_alias_set))
> + if (compare_type_sizes (TREE_TYPE (ref2), type1) >= 0
> + && (same_p2 == -1
> + || base1_alias_set == ref2_alias_set
> + || alias_set_subset_of (base1_alias_set, ref2_alias_set)))
> {
> ++alias_stats.aliasing_component_refs_p_may_alias;
> return true;
> }
> /* If this is ptr vs. decl then we know there is no ptr ... decl path. */
> if (!ref2_is_decl
> - && (base2_alias_set == ref1_alias_set
> + && compare_type_sizes (TREE_TYPE (ref1), type2) >= 0
> + && (same_p1 == -1
> + || base2_alias_set == ref1_alias_set
> || alias_set_subset_of (base2_alias_set, ref1_alias_set)))
> {
> ++alias_stats.aliasing_component_refs_p_may_alias;
> @@ -1221,16 +1295,13 @@ indirect_ref_may_alias_decl_p (tree ref1
> /* If the size of the access relevant for TBAA through the pointer
> is bigger than the size of the decl we can't possibly access the
> decl via that pointer. */
> - if (DECL_SIZE (base2) && COMPLETE_TYPE_P (TREE_TYPE (ptrtype1))
> - && poly_int_tree_p (DECL_SIZE (base2))
> - && poly_int_tree_p (TYPE_SIZE (TREE_TYPE (ptrtype1)))
> - /* ??? This in turn may run afoul when a decl of type T which is
> + if (/* ??? This in turn may run afoul when a decl of type T which is
> a member of union type U is accessed through a pointer to
> type U and sizeof T is smaller than sizeof U. */
> - && TREE_CODE (TREE_TYPE (ptrtype1)) != UNION_TYPE
> + TREE_CODE (TREE_TYPE (ptrtype1)) != UNION_TYPE
> && TREE_CODE (TREE_TYPE (ptrtype1)) != QUAL_UNION_TYPE
> - && known_lt (wi::to_poly_widest (DECL_SIZE (base2)),
> - wi::to_poly_widest (TYPE_SIZE (TREE_TYPE (ptrtype1)))))
> + && compare_sizes (DECL_SIZE (base2),
> + TYPE_SIZE (TREE_TYPE (ptrtype1))) < 0)
> return false;
>
> if (!ref2)
>
--
Richard Biener <rguent...@suse.de>
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany;
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah; HRB 21284 (AG Nürnberg)
