On Thu, Jul 27, 2017 at 2:19 PM, Richard Sandiford
<richard.sandif...@linaro.org> wrote:
> Richard Sandiford <richard.sandif...@linaro.org> writes:
>> Eric Botcazou <ebotca...@adacore.com> writes:
>>> [Sorry for missing the previous messages]
>>>
>>>> Thanks. Just been retesting, and I think I must have forgotten
>>>> to include Ada last time. It turns out that the patch causes a dg-scan
>>>> regression in gnat.dg/vect17.adb, because we now think that if the
>>>> array RECORD_TYPEs *do* alias in:
>>>>
>>>> procedure Add (X, Y : aliased Sarray; R : aliased out Sarray) is
>>>> begin
>>>> for I in Sarray'Range loop
>>>> R(I) := X(I) + Y(I);
>>>> end loop;
>>>> end;
>>>>
>>>> then the dependence distance must be zero. Eric, does that hold true
>>>> for Ada? I.e. if X and R (or Y and R) alias, must it be the case that
>>>> X(I) can only alias R(I) and not for example R(I-1) or R(I+1)?
>>>
>>> Yes, I'd think so (even without the artificial RECORD_TYPE around the
>>> arrays).
>>
>> Good!
>>
>>>> 2017-06-07 Richard Sandiford <richard.sandif...@linaro.org>
>>>>
>>>> gcc/testsuite/
>>>> * gnat.dg/vect17.ads (Sarray): Increase range to 1 .. 5.
>>>> * gnat.dg/vect17.adb (Add): Create a dependence distance of 1
>>>> when X = R or Y = R.
>>>
>>> I think that you need to modify vect15 and vect16 the same way.
>>
>> Ah, yeah. And doing that shows that I'd not handled safelen for
>> DDR_COULD_BE_INDEPENDENT_P. I've fixed that locally.
>>
>> How does this look? Tested on x86_64-linux-gnu both without the
>> vectoriser changes and with the fixed vectoriser patch.
>
> Here's a version of the patch that handles safelen. I split the
> handling out into a new function (vect_analyze_possibly_independent_ddr)
> since it was getting too big to do inline.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
Ok.
Did you check whether BB vectorization is affected? See
vect_slp_analyze_instance_dependence
and friends. It's quite conservative but given the prefetching change
I wonder if we need
to rule out DDR_COULD_BE_INDEPENDENT_P?
Thanks,
Richard.
> Thanks,
> Richard
>
>
> 2017-07-27 Richard Sandiford <richard.sandif...@linaro.org>
>
> gcc/
> * tree-data-ref.h (subscript): Add access_fn field.
> (data_dependence_relation): Add could_be_independent_p.
> (SUB_ACCESS_FN, DDR_COULD_BE_INDEPENDENT_P): New macros.
> (same_access_functions): Move to tree-data-ref.c.
> * tree-data-ref.c (ref_contains_union_access_p): New function.
> (access_fn_component_p): Likewise.
> (access_fn_components_comparable_p): Likewise.
> (dr_analyze_indices): Add a reference to access_fn_component_p.
> (dump_data_dependence_relation): Use SUB_ACCESS_FN instead of
> DR_ACCESS_FN.
> (constant_access_functions): Likewise.
> (add_other_self_distances): Likewise.
> (same_access_functions): Likewise. (Moved from tree-data-ref.h.)
> (initialize_data_dependence_relation): Use XCNEW and remove
> explicit zeroing of DDR_REVERSED_P. Look for a subsequence
> of access functions that have the same type. Allow the
> subsequence to end with different bases in some circumstances.
> Record the chosen access functions in SUB_ACCESS_FN.
> (build_classic_dist_vector_1): Replace ddr_a and ddr_b with
> a_index and b_index. Use SUB_ACCESS_FN instead of DR_ACCESS_FN.
> (subscript_dependence_tester_1): Likewise dra and drb.
> (build_classic_dist_vector): Update calls accordingly.
> (subscript_dependence_tester): Likewise.
> * tree-ssa-loop-prefetch.c (determine_loop_nest_reuse): Check
> DDR_COULD_BE_INDEPENDENT_P.
> * tree-vectorizer.h (LOOP_REQUIRES_VERSIONING_FOR_ALIAS): Test
> comp_alias_ddrs instead of may_alias_ddrs.
> * tree-vect-data-refs.c (vect_analyze_possibly_independent_ddr):
> New function.
> (vect_analyze_data_ref_dependence): Use it if
> DDR_COULD_BE_INDEPENDENT_P, but fall back to using the recorded
> distance vectors if that fails.
> (dependence_distance_ge_vf): New function.
> (vect_prune_runtime_alias_test_list): Use it. Don't clear
> LOOP_VINFO_MAY_ALIAS_DDRS.
>
> gcc/testsuite/
> * gcc.dg/vect/vect-alias-check-3.c: New test.
> * gcc.dg/vect/vect-alias-check-4.c: Likewise.
> * gcc.dg/vect/vect-alias-check-5.c: Likewise.
>
> Index: gcc/tree-data-ref.h
> ===================================================================
> --- gcc/tree-data-ref.h 2017-07-27 13:10:29.620045506 +0100
> +++ gcc/tree-data-ref.h 2017-07-27 13:10:33.023912613 +0100
> @@ -260,6 +260,9 @@ struct conflict_function
>
> struct subscript
> {
> + /* The access functions of the two references. */
> + tree access_fn[2];
> +
> /* A description of the iterations for which the elements are
> accessed twice. */
> conflict_function *conflicting_iterations_in_a;
> @@ -278,6 +281,7 @@ struct subscript
>
> typedef struct subscript *subscript_p;
>
> +#define SUB_ACCESS_FN(SUB, I) (SUB)->access_fn[I]
> #define SUB_CONFLICTS_IN_A(SUB) (SUB)->conflicting_iterations_in_a
> #define SUB_CONFLICTS_IN_B(SUB) (SUB)->conflicting_iterations_in_b
> #define SUB_LAST_CONFLICT(SUB) (SUB)->last_conflict
> @@ -333,6 +337,33 @@ struct data_dependence_relation
> /* Set to true when the dependence relation is on the same data
> access. */
> bool self_reference_p;
> +
> + /* True if the dependence described is conservatively correct rather
> + than exact, and if it is still possible for the accesses to be
> + conditionally independent. For example, the a and b references in:
> +
> + struct s *a, *b;
> + for (int i = 0; i < n; ++i)
> + a->f[i] += b->f[i];
> +
> + conservatively have a distance vector of (0), for the case in which
> + a == b, but the accesses are independent if a != b. Similarly,
> + the a and b references in:
> +
> + struct s *a, *b;
> + for (int i = 0; i < n; ++i)
> + a[0].f[i] += b[i].f[i];
> +
> + conservatively have a distance vector of (0), but they are indepenent
> + when a != b + i. In contrast, the references in:
> +
> + struct s *a;
> + for (int i = 0; i < n; ++i)
> + a->f[i] += a->f[i];
> +
> + have the same distance vector of (0), but the accesses can never be
> + independent. */
> + bool could_be_independent_p;
> };
>
> typedef struct data_dependence_relation *ddr_p;
> @@ -363,6 +394,7 @@ #define DDR_DIR_VECT(DDR, I) \
> #define DDR_DIST_VECT(DDR, I) \
> DDR_DIST_VECTS (DDR)[I]
> #define DDR_REVERSED_P(DDR) (DDR)->reversed_p
> +#define DDR_COULD_BE_INDEPENDENT_P(DDR) (DDR)->could_be_independent_p
>
>
> bool dr_analyze_innermost (innermost_loop_behavior *, tree, struct loop *);
> @@ -457,22 +489,6 @@ same_data_refs (data_reference_p a, data
> return false;
>
> return true;
> -}
> -
> -/* Return true when the DDR contains two data references that have the
> - same access functions. */
> -
> -static inline bool
> -same_access_functions (const struct data_dependence_relation *ddr)
> -{
> - unsigned i;
> -
> - for (i = 0; i < DDR_NUM_SUBSCRIPTS (ddr); i++)
> - if (!eq_evolutions_p (DR_ACCESS_FN (DDR_A (ddr), i),
> - DR_ACCESS_FN (DDR_B (ddr), i)))
> - return false;
> -
> - return true;
> }
>
> /* Returns true when all the dependences are computable. */
> Index: gcc/tree-data-ref.c
> ===================================================================
> --- gcc/tree-data-ref.c 2017-07-27 13:10:29.620045506 +0100
> +++ gcc/tree-data-ref.c 2017-07-27 13:10:33.023912613 +0100
> @@ -124,8 +124,7 @@ Software Foundation; either version 3, o
> } dependence_stats;
>
> static bool subscript_dependence_tester_1 (struct data_dependence_relation *,
> - struct data_reference *,
> - struct data_reference *,
> + unsigned int, unsigned int,
> struct loop *);
> /* Returns true iff A divides B. */
>
> @@ -145,6 +144,21 @@ int_divides_p (int a, int b)
> return ((b % a) == 0);
> }
>
> +/* Return true if reference REF contains a union access. */
> +
> +static bool
> +ref_contains_union_access_p (tree ref)
> +{
> + while (handled_component_p (ref))
> + {
> + ref = TREE_OPERAND (ref, 0);
> + if (TREE_CODE (TREE_TYPE (ref)) == UNION_TYPE
> + || TREE_CODE (TREE_TYPE (ref)) == QUAL_UNION_TYPE)
> + return true;
> + }
> + return false;
> +}
> +
>
>
> /* Dump into FILE all the data references from DATAREFS. */
> @@ -434,13 +448,14 @@ dump_data_dependence_relation (FILE *out
> unsigned int i;
> struct loop *loopi;
>
> - for (i = 0; i < DDR_NUM_SUBSCRIPTS (ddr); i++)
> + subscript *sub;
> + FOR_EACH_VEC_ELT (DDR_SUBSCRIPTS (ddr), i, sub)
> {
> fprintf (outf, " access_fn_A: ");
> - print_generic_stmt (outf, DR_ACCESS_FN (dra, i));
> + print_generic_stmt (outf, SUB_ACCESS_FN (sub, 0));
> fprintf (outf, " access_fn_B: ");
> - print_generic_stmt (outf, DR_ACCESS_FN (drb, i));
> - dump_subscript (outf, DDR_SUBSCRIPT (ddr, i));
> + print_generic_stmt (outf, SUB_ACCESS_FN (sub, 1));
> + dump_subscript (outf, sub);
> }
>
> fprintf (outf, " inner loop index: %d\n", DDR_INNER_LOOP (ddr));
> @@ -920,6 +935,27 @@ dr_analyze_innermost (innermost_loop_beh
> return true;
> }
>
> +/* Return true if OP is a valid component reference for a DR access
> + function. This accepts a subset of what handled_component_p accepts. */
> +
> +static bool
> +access_fn_component_p (tree op)
> +{
> + switch (TREE_CODE (op))
> + {
> + case REALPART_EXPR:
> + case IMAGPART_EXPR:
> + case ARRAY_REF:
> + return true;
> +
> + case COMPONENT_REF:
> + return TREE_CODE (TREE_TYPE (TREE_OPERAND (op, 0))) == RECORD_TYPE;
> +
> + default:
> + return false;
> + }
> +}
> +
> /* Determines the base object and the list of indices of memory reference
> DR, analyzed in LOOP and instantiated in loop nest NEST. */
>
> @@ -957,7 +993,9 @@ dr_analyze_indices (struct data_referenc
> access_fns.safe_push (integer_one_node);
> }
>
> - /* Analyze access functions of dimensions we know to be independent. */
> + /* Analyze access functions of dimensions we know to be independent.
> + The list of component references handled here should be kept in
> + sync with access_fn_component_p. */
> while (handled_component_p (ref))
> {
> if (TREE_CODE (ref) == ARRAY_REF)
> @@ -2148,6 +2186,38 @@ dr_may_alias_p (const struct data_refere
> return refs_may_alias_p (addr_a, addr_b);
> }
>
> +/* REF_A and REF_B both satisfy access_fn_component_p. Return true
> + if it is meaningful to compare their associated access functions
> + when checking for dependencies. */
> +
> +static bool
> +access_fn_components_comparable_p (tree ref_a, tree ref_b)
> +{
> + /* Allow pairs of component refs from the following sets:
> +
> + { REALPART_EXPR, IMAGPART_EXPR }
> + { COMPONENT_REF }
> + { ARRAY_REF }. */
> + tree_code code_a = TREE_CODE (ref_a);
> + tree_code code_b = TREE_CODE (ref_b);
> + if (code_a == IMAGPART_EXPR)
> + code_a = REALPART_EXPR;
> + if (code_b == IMAGPART_EXPR)
> + code_b = REALPART_EXPR;
> + if (code_a != code_b)
> + return false;
> +
> + if (TREE_CODE (ref_a) == COMPONENT_REF)
> + /* ??? We cannot simply use the type of operand #0 of the refs here as
> + the Fortran compiler smuggles type punning into COMPONENT_REFs.
> + Use the DECL_CONTEXT of the FIELD_DECLs instead. */
> + return (DECL_CONTEXT (TREE_OPERAND (ref_a, 1))
> + == DECL_CONTEXT (TREE_OPERAND (ref_b, 1)));
> +
> + return types_compatible_p (TREE_TYPE (TREE_OPERAND (ref_a, 0)),
> + TREE_TYPE (TREE_OPERAND (ref_b, 0)));
> +}
> +
> /* Initialize a data dependence relation between data accesses A and
> B. NB_LOOPS is the number of loops surrounding the references: the
> size of the classic distance/direction vectors. */
> @@ -2160,11 +2230,10 @@ initialize_data_dependence_relation (str
> struct data_dependence_relation *res;
> unsigned int i;
>
> - res = XNEW (struct data_dependence_relation);
> + res = XCNEW (struct data_dependence_relation);
> DDR_A (res) = a;
> DDR_B (res) = b;
> DDR_LOOP_NEST (res).create (0);
> - DDR_REVERSED_P (res) = false;
> DDR_SUBSCRIPTS (res).create (0);
> DDR_DIR_VECTS (res).create (0);
> DDR_DIST_VECTS (res).create (0);
> @@ -2182,82 +2251,277 @@ initialize_data_dependence_relation (str
> return res;
> }
>
> - /* The case where the references are exactly the same. */
> - if (operand_equal_p (DR_REF (a), DR_REF (b), 0))
> + unsigned int num_dimensions_a = DR_NUM_DIMENSIONS (a);
> + unsigned int num_dimensions_b = DR_NUM_DIMENSIONS (b);
> + if (num_dimensions_a == 0 || num_dimensions_b == 0)
> {
> - if ((loop_nest.exists ()
> - && !object_address_invariant_in_loop_p (loop_nest[0],
> - DR_BASE_OBJECT (a)))
> - || DR_NUM_DIMENSIONS (a) == 0)
> + DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> + return res;
> + }
> +
> + /* For unconstrained bases, the root (highest-indexed) subscript
> + describes a variation in the base of the original DR_REF rather
> + than a component access. We have no type that accurately describes
> + the new DR_BASE_OBJECT (whose TREE_TYPE describes the type *after*
> + applying this subscript) so limit the search to the last real
> + component access.
> +
> + E.g. for:
> +
> + void
> + f (int a[][8], int b[][8])
> + {
> + for (int i = 0; i < 8; ++i)
> + a[i * 2][0] = b[i][0];
> + }
> +
> + the a and b accesses have a single ARRAY_REF component reference [0]
> + but have two subscripts. */
> + if (DR_UNCONSTRAINED_BASE (a))
> + num_dimensions_a -= 1;
> + if (DR_UNCONSTRAINED_BASE (b))
> + num_dimensions_b -= 1;
> +
> + /* These structures describe sequences of component references in
> + DR_REF (A) and DR_REF (B). Each component reference is tied to a
> + specific access function. */
> + struct {
> + /* The sequence starts at DR_ACCESS_FN (A, START_A) of A and
> + DR_ACCESS_FN (B, START_B) of B (inclusive) and extends to higher
> + indices. In C notation, these are the indices of the rightmost
> + component references; e.g. for a sequence .b.c.d, the start
> + index is for .d. */
> + unsigned int start_a;
> + unsigned int start_b;
> +
> + /* The sequence contains LENGTH consecutive access functions from
> + each DR. */
> + unsigned int length;
> +
> + /* The enclosing objects for the A and B sequences respectively,
> + i.e. the objects to which DR_ACCESS_FN (A, START_A + LENGTH - 1)
> + and DR_ACCESS_FN (B, START_B + LENGTH - 1) are applied. */
> + tree object_a;
> + tree object_b;
> + } full_seq = {}, struct_seq = {};
> +
> + /* Before each iteration of the loop:
> +
> + - REF_A is what you get after applying DR_ACCESS_FN (A, INDEX_A) and
> + - REF_B is what you get after applying DR_ACCESS_FN (B, INDEX_B). */
> + unsigned int index_a = 0;
> + unsigned int index_b = 0;
> + tree ref_a = DR_REF (a);
> + tree ref_b = DR_REF (b);
> +
> + /* Now walk the component references from the final DR_REFs back up to
> + the enclosing base objects. Each component reference corresponds
> + to one access function in the DR, with access function 0 being for
> + the final DR_REF and the highest-indexed access function being the
> + one that is applied to the base of the DR.
> +
> + Look for a sequence of component references whose access functions
> + are comparable (see access_fn_components_comparable_p). If more
> + than one such sequence exists, pick the one nearest the base
> + (which is the leftmost sequence in C notation). Store this sequence
> + in FULL_SEQ.
> +
> + For example, if we have:
> +
> + struct foo { struct bar s; ... } (*a)[10], (*b)[10];
> +
> + A: a[0][i].s.c.d
> + B: __real b[0][i].s.e[i].f
> +
> + (where d is the same type as the real component of f) then the access
> + functions would be:
> +
> + 0 1 2 3
> + A: .d .c .s [i]
> +
> + 0 1 2 3 4 5
> + B: __real .f [i] .e .s [i]
> +
> + The A0/B2 column isn't comparable, since .d is a COMPONENT_REF
> + and [i] is an ARRAY_REF. However, the A1/B3 column contains two
> + COMPONENT_REF accesses for struct bar, so is comparable. Likewise
> + the A2/B4 column contains two COMPONENT_REF accesses for struct foo,
> + so is comparable. The A3/B5 column contains two ARRAY_REFs that
> + index foo[10] arrays, so is again comparable. The sequence is
> + therefore:
> +
> + A: [1, 3] (i.e. [i].s.c)
> + B: [3, 5] (i.e. [i].s.e)
> +
> + Also look for sequences of component references whose access
> + functions are comparable and whose enclosing objects have the same
> + RECORD_TYPE. Store this sequence in STRUCT_SEQ. In the above
> + example, STRUCT_SEQ would be:
> +
> + A: [1, 2] (i.e. s.c)
> + B: [3, 4] (i.e. s.e) */
> + while (index_a < num_dimensions_a && index_b < num_dimensions_b)
> + {
> + /* REF_A and REF_B must be one of the component access types
> + allowed by dr_analyze_indices. */
> + gcc_checking_assert (access_fn_component_p (ref_a));
> + gcc_checking_assert (access_fn_component_p (ref_b));
> +
> + /* Get the immediately-enclosing objects for REF_A and REF_B,
> + i.e. the references *before* applying DR_ACCESS_FN (A, INDEX_A)
> + and DR_ACCESS_FN (B, INDEX_B). */
> + tree object_a = TREE_OPERAND (ref_a, 0);
> + tree object_b = TREE_OPERAND (ref_b, 0);
> +
> + tree type_a = TREE_TYPE (object_a);
> + tree type_b = TREE_TYPE (object_b);
> + if (access_fn_components_comparable_p (ref_a, ref_b))
> + {
> + /* This pair of component accesses is comparable for dependence
> + analysis, so we can include DR_ACCESS_FN (A, INDEX_A) and
> + DR_ACCESS_FN (B, INDEX_B) in the sequence. */
> + if (full_seq.start_a + full_seq.length != index_a
> + || full_seq.start_b + full_seq.length != index_b)
> + {
> + /* The accesses don't extend the current sequence,
> + so start a new one here. */
> + full_seq.start_a = index_a;
> + full_seq.start_b = index_b;
> + full_seq.length = 0;
> + }
> +
> + /* Add this pair of references to the sequence. */
> + full_seq.length += 1;
> + full_seq.object_a = object_a;
> + full_seq.object_b = object_b;
> +
> + /* If the enclosing objects are structures (and thus have the
> + same RECORD_TYPE), record the new sequence in STRUCT_SEQ. */
> + if (TREE_CODE (type_a) == RECORD_TYPE)
> + struct_seq = full_seq;
> +
> + /* Move to the next containing reference for both A and B. */
> + ref_a = object_a;
> + ref_b = object_b;
> + index_a += 1;
> + index_b += 1;
> + continue;
> + }
> +
> + /* Try to approach equal type sizes. */
> + if (!COMPLETE_TYPE_P (type_a)
> + || !COMPLETE_TYPE_P (type_b)
> + || !tree_fits_uhwi_p (TYPE_SIZE_UNIT (type_a))
> + || !tree_fits_uhwi_p (TYPE_SIZE_UNIT (type_b)))
> + break;
> +
> + unsigned HOST_WIDE_INT size_a = tree_to_uhwi (TYPE_SIZE_UNIT (type_a));
> + unsigned HOST_WIDE_INT size_b = tree_to_uhwi (TYPE_SIZE_UNIT (type_b));
> + if (size_a <= size_b)
> {
> - DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> - return res;
> + index_a += 1;
> + ref_a = object_a;
> + }
> + if (size_b <= size_a)
> + {
> + index_b += 1;
> + ref_b = object_b;
> }
> - DDR_AFFINE_P (res) = true;
> - DDR_ARE_DEPENDENT (res) = NULL_TREE;
> - DDR_SUBSCRIPTS (res).create (DR_NUM_DIMENSIONS (a));
> - DDR_LOOP_NEST (res) = loop_nest;
> - DDR_INNER_LOOP (res) = 0;
> - DDR_SELF_REFERENCE (res) = true;
> - for (i = 0; i < DR_NUM_DIMENSIONS (a); i++)
> - {
> - struct subscript *subscript;
> -
> - subscript = XNEW (struct subscript);
> - SUB_CONFLICTS_IN_A (subscript) = conflict_fn_not_known ();
> - SUB_CONFLICTS_IN_B (subscript) = conflict_fn_not_known ();
> - SUB_LAST_CONFLICT (subscript) = chrec_dont_know;
> - SUB_DISTANCE (subscript) = chrec_dont_know;
> - DDR_SUBSCRIPTS (res).safe_push (subscript);
> - }
> - return res;
> }
>
> - /* If the references do not access the same object, we do not know
> - whether they alias or not. We do not care about TBAA or alignment
> - info so we can use OEP_ADDRESS_OF to avoid false negatives.
> - But the accesses have to use compatible types as otherwise the
> - built indices would not match. */
> - if (!operand_equal_p (DR_BASE_OBJECT (a), DR_BASE_OBJECT (b),
> OEP_ADDRESS_OF)
> - || !types_compatible_p (TREE_TYPE (DR_BASE_OBJECT (a)),
> - TREE_TYPE (DR_BASE_OBJECT (b))))
> + /* See whether FULL_SEQ ends at the base and whether the two bases
> + are equal. We do not care about TBAA or alignment info so we can
> + use OEP_ADDRESS_OF to avoid false negatives. */
> + tree base_a = DR_BASE_OBJECT (a);
> + tree base_b = DR_BASE_OBJECT (b);
> + bool same_base_p = (full_seq.start_a + full_seq.length == num_dimensions_a
> + && full_seq.start_b + full_seq.length ==
> num_dimensions_b
> + && DR_UNCONSTRAINED_BASE (a) == DR_UNCONSTRAINED_BASE
> (b)
> + && operand_equal_p (base_a, base_b, OEP_ADDRESS_OF)
> + && types_compatible_p (TREE_TYPE (base_a),
> + TREE_TYPE (base_b))
> + && (!loop_nest.exists ()
> + || (object_address_invariant_in_loop_p
> + (loop_nest[0], base_a))));
> +
> + /* If the bases are the same, we can include the base variation too.
> + E.g. the b accesses in:
> +
> + for (int i = 0; i < n; ++i)
> + b[i + 4][0] = b[i][0];
> +
> + have a definite dependence distance of 4, while for:
> +
> + for (int i = 0; i < n; ++i)
> + a[i + 4][0] = b[i][0];
> +
> + the dependence distance depends on the gap between a and b.
> +
> + If the bases are different then we can only rely on the sequence
> + rooted at a structure access, since arrays are allowed to overlap
> + arbitrarily and change shape arbitrarily. E.g. we treat this as
> + valid code:
> +
> + int a[256];
> + ...
> + ((int (*)[4][3]) &a[1])[i][0] += ((int (*)[4][3]) &a[2])[i][0];
> +
> + where two lvalues with the same int[4][3] type overlap, and where
> + both lvalues are distinct from the object's declared type. */
> + if (same_base_p)
> {
> - DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> - return res;
> + if (DR_UNCONSTRAINED_BASE (a))
> + full_seq.length += 1;
> }
> + else
> + full_seq = struct_seq;
>
> - /* If the base of the object is not invariant in the loop nest, we cannot
> - analyze it. TODO -- in fact, it would suffice to record that there may
> - be arbitrary dependences in the loops where the base object varies. */
> - if ((loop_nest.exists ()
> - && !object_address_invariant_in_loop_p (loop_nest[0], DR_BASE_OBJECT
> (a)))
> - || DR_NUM_DIMENSIONS (a) == 0)
> + /* Punt if we didn't find a suitable sequence. */
> + if (full_seq.length == 0)
> {
> DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> return res;
> }
>
> - /* If the number of dimensions of the access to not agree we can have
> - a pointer access to a component of the array element type and an
> - array access while the base-objects are still the same. Punt. */
> - if (DR_NUM_DIMENSIONS (a) != DR_NUM_DIMENSIONS (b))
> + if (!same_base_p)
> {
> - DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> - return res;
> + /* Partial overlap is possible for different bases when strict aliasing
> + is not in effect. It's also possible if either base involves a union
> + access; e.g. for:
> +
> + struct s1 { int a[2]; };
> + struct s2 { struct s1 b; int c; };
> + struct s3 { int d; struct s1 e; };
> + union u { struct s2 f; struct s3 g; } *p, *q;
> +
> + the s1 at "p->f.b" (base "p->f") partially overlaps the s1 at
> + "p->g.e" (base "p->g") and might partially overlap the s1 at
> + "q->g.e" (base "q->g"). */
> + if (!flag_strict_aliasing
> + || ref_contains_union_access_p (full_seq.object_a)
> + || ref_contains_union_access_p (full_seq.object_b))
> + {
> + DDR_ARE_DEPENDENT (res) = chrec_dont_know;
> + return res;
> + }
> +
> + DDR_COULD_BE_INDEPENDENT_P (res) = true;
> }
>
> DDR_AFFINE_P (res) = true;
> DDR_ARE_DEPENDENT (res) = NULL_TREE;
> - DDR_SUBSCRIPTS (res).create (DR_NUM_DIMENSIONS (a));
> + DDR_SUBSCRIPTS (res).create (full_seq.length);
> DDR_LOOP_NEST (res) = loop_nest;
> DDR_INNER_LOOP (res) = 0;
> DDR_SELF_REFERENCE (res) = false;
>
> - for (i = 0; i < DR_NUM_DIMENSIONS (a); i++)
> + for (i = 0; i < full_seq.length; ++i)
> {
> struct subscript *subscript;
>
> subscript = XNEW (struct subscript);
> + SUB_ACCESS_FN (subscript, 0) = DR_ACCESS_FN (a, full_seq.start_a + i);
> + SUB_ACCESS_FN (subscript, 1) = DR_ACCESS_FN (b, full_seq.start_b + i);
> SUB_CONFLICTS_IN_A (subscript) = conflict_fn_not_known ();
> SUB_CONFLICTS_IN_B (subscript) = conflict_fn_not_known ();
> SUB_LAST_CONFLICT (subscript) = chrec_dont_know;
> @@ -3839,14 +4103,15 @@ add_outer_distances (struct data_depende
> }
>
> /* Return false when fail to represent the data dependence as a
> - distance vector. INIT_B is set to true when a component has been
> + distance vector. A_INDEX is the index of the first reference
> + (0 for DDR_A, 1 for DDR_B) and B_INDEX is the index of the
> + second reference. INIT_B is set to true when a component has been
> added to the distance vector DIST_V. INDEX_CARRY is then set to
> the index in DIST_V that carries the dependence. */
>
> static bool
> build_classic_dist_vector_1 (struct data_dependence_relation *ddr,
> - struct data_reference *ddr_a,
> - struct data_reference *ddr_b,
> + unsigned int a_index, unsigned int b_index,
> lambda_vector dist_v, bool *init_b,
> int *index_carry)
> {
> @@ -3864,8 +4129,8 @@ build_classic_dist_vector_1 (struct data
> return false;
> }
>
> - access_fn_a = DR_ACCESS_FN (ddr_a, i);
> - access_fn_b = DR_ACCESS_FN (ddr_b, i);
> + access_fn_a = SUB_ACCESS_FN (subscript, a_index);
> + access_fn_b = SUB_ACCESS_FN (subscript, b_index);
>
> if (TREE_CODE (access_fn_a) == POLYNOMIAL_CHREC
> && TREE_CODE (access_fn_b) == POLYNOMIAL_CHREC)
> @@ -3925,10 +4190,11 @@ build_classic_dist_vector_1 (struct data
> constant_access_functions (const struct data_dependence_relation *ddr)
> {
> unsigned i;
> + subscript *sub;
>
> - for (i = 0; i < DDR_NUM_SUBSCRIPTS (ddr); i++)
> - if (!evolution_function_is_constant_p (DR_ACCESS_FN (DDR_A (ddr), i))
> - || !evolution_function_is_constant_p (DR_ACCESS_FN (DDR_B (ddr), i)))
> + FOR_EACH_VEC_ELT (DDR_SUBSCRIPTS (ddr), i, sub)
> + if (!evolution_function_is_constant_p (SUB_ACCESS_FN (sub, 0))
> + || !evolution_function_is_constant_p (SUB_ACCESS_FN (sub, 1)))
> return false;
>
> return true;
> @@ -3991,10 +4257,11 @@ add_other_self_distances (struct data_de
> lambda_vector dist_v;
> unsigned i;
> int index_carry = DDR_NB_LOOPS (ddr);
> + subscript *sub;
>
> - for (i = 0; i < DDR_NUM_SUBSCRIPTS (ddr); i++)
> + FOR_EACH_VEC_ELT (DDR_SUBSCRIPTS (ddr), i, sub)
> {
> - tree access_fun = DR_ACCESS_FN (DDR_A (ddr), i);
> + tree access_fun = SUB_ACCESS_FN (sub, 0);
>
> if (TREE_CODE (access_fun) == POLYNOMIAL_CHREC)
> {
> @@ -4006,7 +4273,7 @@ add_other_self_distances (struct data_de
> return;
> }
>
> - access_fun = DR_ACCESS_FN (DDR_A (ddr), 0);
> + access_fun = SUB_ACCESS_FN (DDR_SUBSCRIPT (ddr, 0), 0);
>
> if (TREE_CODE (CHREC_LEFT (access_fun)) == POLYNOMIAL_CHREC)
> add_multivariate_self_dist (ddr, access_fun);
> @@ -4077,6 +4344,23 @@ add_distance_for_zero_overlaps (struct d
> }
> }
>
> +/* Return true when the DDR contains two data references that have the
> + same access functions. */
> +
> +static inline bool
> +same_access_functions (const struct data_dependence_relation *ddr)
> +{
> + unsigned i;
> + subscript *sub;
> +
> + FOR_EACH_VEC_ELT (DDR_SUBSCRIPTS (ddr), i, sub)
> + if (!eq_evolutions_p (SUB_ACCESS_FN (sub, 0),
> + SUB_ACCESS_FN (sub, 1)))
> + return false;
> +
> + return true;
> +}
> +
> /* Compute the classic per loop distance vector. DDR is the data
> dependence relation to build a vector from. Return false when fail
> to represent the data dependence as a distance vector. */
> @@ -4108,8 +4392,7 @@ build_classic_dist_vector (struct data_d
> }
>
> dist_v = lambda_vector_new (DDR_NB_LOOPS (ddr));
> - if (!build_classic_dist_vector_1 (ddr, DDR_A (ddr), DDR_B (ddr),
> - dist_v, &init_b, &index_carry))
> + if (!build_classic_dist_vector_1 (ddr, 0, 1, dist_v, &init_b,
> &index_carry))
> return false;
>
> /* Save the distance vector if we initialized one. */
> @@ -4142,12 +4425,11 @@ build_classic_dist_vector (struct data_d
> if (!lambda_vector_lexico_pos (dist_v, DDR_NB_LOOPS (ddr)))
> {
> lambda_vector save_v = lambda_vector_new (DDR_NB_LOOPS (ddr));
> - if (!subscript_dependence_tester_1 (ddr, DDR_B (ddr), DDR_A (ddr),
> - loop_nest))
> + if (!subscript_dependence_tester_1 (ddr, 1, 0, loop_nest))
> return false;
> compute_subscript_distance (ddr);
> - if (!build_classic_dist_vector_1 (ddr, DDR_B (ddr), DDR_A (ddr),
> - save_v, &init_b, &index_carry))
> + if (!build_classic_dist_vector_1 (ddr, 1, 0, save_v, &init_b,
> + &index_carry))
> return false;
> save_dist_v (ddr, save_v);
> DDR_REVERSED_P (ddr) = true;
> @@ -4183,12 +4465,10 @@ build_classic_dist_vector (struct data_d
> {
> lambda_vector opposite_v = lambda_vector_new (DDR_NB_LOOPS
> (ddr));
>
> - if (!subscript_dependence_tester_1 (ddr, DDR_B (ddr),
> - DDR_A (ddr), loop_nest))
> + if (!subscript_dependence_tester_1 (ddr, 1, 0, loop_nest))
> return false;
> compute_subscript_distance (ddr);
> - if (!build_classic_dist_vector_1 (ddr, DDR_B (ddr), DDR_A (ddr),
> - opposite_v, &init_b,
> + if (!build_classic_dist_vector_1 (ddr, 1, 0, opposite_v,
> &init_b,
> &index_carry))
> return false;
>
> @@ -4267,13 +4547,13 @@ build_classic_dir_vector (struct data_de
> }
> }
>
> -/* Helper function. Returns true when there is a dependence between
> - data references DRA and DRB. */
> +/* Helper function. Returns true when there is a dependence between the
> + data references. A_INDEX is the index of the first reference (0 for
> + DDR_A, 1 for DDR_B) and B_INDEX is the index of the second reference. */
>
> static bool
> subscript_dependence_tester_1 (struct data_dependence_relation *ddr,
> - struct data_reference *dra,
> - struct data_reference *drb,
> + unsigned int a_index, unsigned int b_index,
> struct loop *loop_nest)
> {
> unsigned int i;
> @@ -4285,8 +4565,8 @@ subscript_dependence_tester_1 (struct da
> {
> conflict_function *overlaps_a, *overlaps_b;
>
> - analyze_overlapping_iterations (DR_ACCESS_FN (dra, i),
> - DR_ACCESS_FN (drb, i),
> + analyze_overlapping_iterations (SUB_ACCESS_FN (subscript, a_index),
> + SUB_ACCESS_FN (subscript, b_index),
> &overlaps_a, &overlaps_b,
> &last_conflicts, loop_nest);
>
> @@ -4335,7 +4615,7 @@ subscript_dependence_tester_1 (struct da
> subscript_dependence_tester (struct data_dependence_relation *ddr,
> struct loop *loop_nest)
> {
> - if (subscript_dependence_tester_1 (ddr, DDR_A (ddr), DDR_B (ddr),
> loop_nest))
> + if (subscript_dependence_tester_1 (ddr, 0, 1, loop_nest))
> dependence_stats.num_dependence_dependent++;
>
> compute_subscript_distance (ddr);
> Index: gcc/tree-ssa-loop-prefetch.c
> ===================================================================
> --- gcc/tree-ssa-loop-prefetch.c 2017-07-27 13:10:29.620045506 +0100
> +++ gcc/tree-ssa-loop-prefetch.c 2017-07-27 13:10:33.023912613 +0100
> @@ -1668,6 +1668,7 @@ determine_loop_nest_reuse (struct loop *
> refb = (struct mem_ref *) DDR_B (dep)->aux;
>
> if (DDR_ARE_DEPENDENT (dep) == chrec_dont_know
> + || DDR_COULD_BE_INDEPENDENT_P (dep)
> || DDR_NUM_DIST_VECTS (dep) == 0)
> {
> /* If the dependence cannot be analyzed, assume that there might be
> Index: gcc/tree-vectorizer.h
> ===================================================================
> --- gcc/tree-vectorizer.h 2017-07-27 13:10:29.620045506 +0100
> +++ gcc/tree-vectorizer.h 2017-07-27 13:10:33.024912868 +0100
> @@ -358,7 +358,7 @@ #define LOOP_VINFO_ORIG_LOOP_INFO(L)
> #define LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT(L) \
> ((L)->may_misalign_stmts.length () > 0)
> #define LOOP_REQUIRES_VERSIONING_FOR_ALIAS(L) \
> - ((L)->may_alias_ddrs.length () > 0)
> + ((L)->comp_alias_ddrs.length () > 0)
> #define LOOP_REQUIRES_VERSIONING_FOR_NITERS(L) \
> (LOOP_VINFO_NITERS_ASSUMPTIONS (L))
> #define LOOP_REQUIRES_VERSIONING(L) \
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c 2017-07-27 13:10:29.620045506 +0100
> +++ gcc/tree-vect-data-refs.c 2017-07-27 13:10:33.024912868 +0100
> @@ -160,6 +160,60 @@ vect_mark_for_runtime_alias_test (ddr_p
> }
>
>
> +/* A subroutine of vect_analyze_data_ref_dependence. Handle
> + DDR_COULD_BE_INDEPENDENT_P ddr DDR that has a known set of dependence
> + distances. These distances are conservatively correct but they don't
> + reflect a guaranteed dependence.
> +
> + Return true if this function does all the work necessary to avoid
> + an alias or false if the caller should use the dependence distances
> + to limit the vectorization factor in the usual way. LOOP_DEPTH is
> + the depth of the loop described by LOOP_VINFO and the other arguments
> + are as for vect_analyze_data_ref_dependence. */
> +
> +static bool
> +vect_analyze_possibly_independent_ddr (data_dependence_relation *ddr,
> + loop_vec_info loop_vinfo,
> + int loop_depth, int *max_vf)
> +{
> + struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
> + lambda_vector dist_v;
> + unsigned int i;
> + FOR_EACH_VEC_ELT (DDR_DIST_VECTS (ddr), i, dist_v)
> + {
> + int dist = dist_v[loop_depth];
> + if (dist != 0 && !(dist > 0 && DDR_REVERSED_P (ddr)))
> + {
> + /* If the user asserted safelen >= DIST consecutive iterations
> + can be executed concurrently, assume independence.
> +
> + ??? An alternative would be to add the alias check even
> + in this case, and vectorize the fallback loop with the
> + maximum VF set to safelen. However, if the user has
> + explicitly given a length, it's less likely that that
> + would be a win. */
> + if (loop->safelen >= 2 && abs_hwi (dist) <= loop->safelen)
> + {
> + if (loop->safelen < *max_vf)
> + *max_vf = loop->safelen;
> + LOOP_VINFO_NO_DATA_DEPENDENCIES (loop_vinfo) = false;
> + continue;
> + }
> +
> + /* For dependence distances of 2 or more, we have the option
> + of limiting VF or checking for an alias at runtime.
> + Prefer to check at runtime if we can, to avoid limiting
> + the VF unnecessarily when the bases are in fact independent.
> +
> + Note that the alias checks will be removed if the VF ends up
> + being small enough. */
> + return vect_mark_for_runtime_alias_test (ddr, loop_vinfo);
> + }
> + }
> + return true;
> +}
> +
> +
> /* Function vect_analyze_data_ref_dependence.
>
> Return TRUE if there (might) exist a dependence between a memory-reference
> @@ -305,6 +359,12 @@ vect_analyze_data_ref_dependence (struct
> }
>
> loop_depth = index_in_loop_nest (loop->num, DDR_LOOP_NEST (ddr));
> +
> + if (DDR_COULD_BE_INDEPENDENT_P (ddr)
> + && vect_analyze_possibly_independent_ddr (ddr, loop_vinfo,
> + loop_depth, max_vf))
> + return false;
> +
> FOR_EACH_VEC_ELT (DDR_DIST_VECTS (ddr), i, dist_v)
> {
> int dist = dist_v[loop_depth];
> @@ -2878,6 +2938,44 @@ vect_no_alias_p (struct data_reference *
> return false;
> }
>
> +/* Return true if the minimum nonzero dependence distance for loop LOOP_DEPTH
> + in DDR is >= VF. */
> +
> +static bool
> +dependence_distance_ge_vf (data_dependence_relation *ddr,
> + unsigned int loop_depth, unsigned HOST_WIDE_INT vf)
> +{
> + if (DDR_ARE_DEPENDENT (ddr) != NULL_TREE
> + || DDR_NUM_DIST_VECTS (ddr) == 0)
> + return false;
> +
> + /* If the dependence is exact, we should have limited the VF instead. */
> + gcc_checking_assert (DDR_COULD_BE_INDEPENDENT_P (ddr));
> +
> + unsigned int i;
> + lambda_vector dist_v;
> + FOR_EACH_VEC_ELT (DDR_DIST_VECTS (ddr), i, dist_v)
> + {
> + HOST_WIDE_INT dist = dist_v[loop_depth];
> + if (dist != 0
> + && !(dist > 0 && DDR_REVERSED_P (ddr))
> + && (unsigned HOST_WIDE_INT) abs_hwi (dist) < vf)
> + return false;
> + }
> +
> + if (dump_enabled_p ())
> + {
> + dump_printf_loc (MSG_NOTE, vect_location,
> + "dependence distance between ");
> + dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (DDR_A (ddr)));
> + dump_printf (MSG_NOTE, " and ");
> + dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (DDR_B (ddr)));
> + dump_printf (MSG_NOTE, " is >= VF\n");
> + }
> +
> + return true;
> +}
> +
> /* Function vect_prune_runtime_alias_test_list.
>
> Prune a list of ddrs to be tested at run-time by versioning for alias.
> @@ -2908,6 +3006,10 @@ vect_prune_runtime_alias_test_list (loop
>
> comp_alias_ddrs.create (may_alias_ddrs.length ());
>
> + unsigned int loop_depth
> + = index_in_loop_nest (LOOP_VINFO_LOOP (loop_vinfo)->num,
> + LOOP_VINFO_LOOP_NEST (loop_vinfo));
> +
> /* First, we collect all data ref pairs for aliasing checks. */
> FOR_EACH_VEC_ELT (may_alias_ddrs, i, ddr)
> {
> @@ -2917,6 +3019,11 @@ vect_prune_runtime_alias_test_list (loop
> tree segment_length_a, segment_length_b;
> gimple *stmt_a, *stmt_b;
>
> + /* Ignore the alias if the VF we chose ended up being no greater
> + than the dependence distance. */
> + if (dependence_distance_ge_vf (ddr, loop_depth, vect_factor))
> + continue;
> +
> dr_a = DDR_A (ddr);
> stmt_a = DR_STMT (DDR_A (ddr));
> dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
> @@ -2993,10 +3100,6 @@ vect_prune_runtime_alias_test_list (loop
> return false;
> }
>
> - /* All alias checks have been resolved at compilation time. */
> - if (!comp_alias_ddrs.length ())
> - LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo).truncate (0);
> -
> return true;
> }
>
> Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-3.c
> ===================================================================
> --- /dev/null 2017-07-27 10:25:31.671280760 +0100
> +++ gcc/testsuite/gcc.dg/vect/vect-alias-check-3.c 2017-07-27
> 13:10:33.022912357 +0100
> @@ -0,0 +1,120 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-additional-options "--param vect-max-version-for-alias-checks=0
> -fopenmp-simd" } */
> +
> +/* Intended to be larger than any VF. */
> +#define GAP 128
> +#define N (GAP * 3)
> +
> +struct s { int x[N + 1]; };
> +struct t { struct s x[N + 1]; };
> +struct u { int x[N + 1]; int y; };
> +struct v { struct s s; };
> +
> +void
> +f1 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->x[i] += b->x[i];
> +}
> +
> +void
> +f2 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[1].x[i] += b[2].x[i];
> +}
> +
> +void
> +f3 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[1].x[i] += b[i].x[i];
> +}
> +
> +void
> +f4 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[i].x[i] += b[i].x[i];
> +}
> +
> +void
> +f5 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->x[i] += b->x[i + 1];
> +}
> +
> +void
> +f6 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[1].x[i] += b[2].x[i + 1];
> +}
> +
> +void
> +f7 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[1].x[i] += b[i].x[i + 1];
> +}
> +
> +void
> +f8 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a[i].x[i] += b[i].x[i + 1];
> +}
> +
> +void
> +f9 (struct s *a, struct t *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->x[i] += b->x[1].x[i];
> +}
> +
> +void
> +f10 (struct s *a, struct t *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->x[i] += b->x[i].x[i];
> +}
> +
> +void
> +f11 (struct u *a, struct u *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->x[i] += b->x[i] + b[i].y;
> +}
> +
> +void
> +f12 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < GAP; ++i)
> + a->x[i + GAP] += b->x[i];
> +}
> +
> +void
> +f13 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < GAP * 2; ++i)
> + a->x[i + GAP] += b->x[i];
> +}
> +
> +void
> +f14 (struct v *a, struct s *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->s.x[i] = b->x[i];
> +}
> +
> +void
> +f15 (struct s *a, struct s *b)
> +{
> + #pragma omp simd safelen(N)
> + for (int i = 0; i < N; ++i)
> + a->x[i + 1] += b->x[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 15 "vect" } } */
> Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-4.c
> ===================================================================
> --- /dev/null 2017-07-27 10:25:31.671280760 +0100
> +++ gcc/testsuite/gcc.dg/vect/vect-alias-check-4.c 2017-07-27
> 13:10:33.022912357 +0100
> @@ -0,0 +1,35 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +/* { dg-additional-options "--param vect-max-version-for-alias-checks=0" } */
> +
> +#define N 16
> +
> +struct s1 { int a[N]; };
> +struct s2 { struct s1 b; int c; };
> +struct s3 { int d; struct s1 e; };
> +union u { struct s2 f; struct s3 g; };
> +
> +/* We allow a and b to overlap arbitrarily. */
> +
> +void
> +f1 (int a[][N], int b[][N])
> +{
> + for (int i = 0; i < N; ++i)
> + a[0][i] += b[0][i];
> +}
> +
> +void
> +f2 (union u *a, union u *b)
> +{
> + for (int i = 0; i < N; ++i)
> + a->f.b.a[i] += b->g.e.a[i];
> +}
> +
> +void
> +f3 (struct s1 *a, struct s1 *b)
> +{
> + for (int i = 0; i < N - 1; ++i)
> + a->a[i + 1] += b->a[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-not "LOOP VECTORIZED" "vect" } } */
> Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-5.c
> ===================================================================
> --- /dev/null 2017-07-27 10:25:31.671280760 +0100
> +++ gcc/testsuite/gcc.dg/vect/vect-alias-check-5.c 2017-07-27
> 13:10:33.022912357 +0100
> @@ -0,0 +1,19 @@
> +/* { dg-do compile } */
> +/* { dg-require-effective-target vect_int } */
> +
> +/* Intended to be larger than any VF. */
> +#define GAP 128
> +#define N (GAP * 3)
> +
> +struct s { int x[N]; };
> +
> +void
> +f1 (struct s *a, struct s *b)
> +{
> + for (int i = 0; i < GAP * 2; ++i)
> + a->x[i + GAP] += b->x[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-times "consider run-time aliasing" 1 "vect" }
> } */
> +/* { dg-final { scan-tree-dump-times "improved number of alias checks from 1
> to 0" 1 "vect" } } */
> +/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 1 "vect" } } */
