"Bin.Cheng" <amker.ch...@gmail.com> writes:
> On Wed, May 3, 2017 at 9:00 AM, Richard Sandiford
> <richard.sandif...@linaro.org> wrote:
>> Index: gcc/tree-data-ref.h
>> ===================================================================
>> --- gcc/tree-data-ref.h 2017-05-03 08:48:11.977015306 +0100
>> +++ gcc/tree-data-ref.h 2017-05-03 08:48:48.737038502 +0100
>> @@ -191,6 +191,9 @@ struct conflict_function
>>
>> struct subscript
>> {
>> + /* The access functions of the two references. */
>> + tree access_fn[2];
> Is it better to follow existing code, i.e, name this as
> access_fn_a/access_fn_b. Thus we don't need to use const value 0/1 in
> various places, which is a little bit confusing.
[Answered below]
>> +
>> /* A description of the iterations for which the elements are
>> accessed twice. */
>> conflict_function *conflicting_iterations_in_a;
>> @@ -209,6 +212,7 @@ 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
>> @@ -264,6 +268,33 @@ 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;
>> @@ -294,6 +325,7 @@ #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 (struct data_reference *, struct loop *);
>> @@ -372,22 +404,6 @@ 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 2017-02-23 19:54:15.000000000 +0000
>> +++ gcc/tree-data-ref.c 2017-05-03 08:48:48.737038502 +0100
>> @@ -123,8 +123,7 @@ 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 *);
> As mentioned, how about passing access_fn directly, rather than less
> meaningful 0/1 values?
The problem is that access_fn is a property of the individual
subscripts, whereas this is operating on a full data_reference.
One alternative would be to use conditions like:
first_is_a ? SUB_ACCESS_FN_A (sub) : SUB_ACCESS_FN_B (sub)
but IMO that's less readable than the existing:
SUB_ACCESS_FN (sub, index)
Or we could have individual access_fn arrays for A and B, separate
from the main subscript array, but that would mean allocating three
arrays instead of one.
>> /* Returns true iff A divides B. */
>>
>> @@ -144,6 +143,21 @@ 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. */
>> @@ -433,13 +447,14 @@ 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), 0);
>> + print_generic_stmt (outf, SUB_ACCESS_FN (sub, 0), 0);
>> fprintf (outf, " access_fn_B: ");
>> - print_generic_stmt (outf, DR_ACCESS_FN (drb, i), 0);
>> - dump_subscript (outf, DDR_SUBSCRIPT (ddr, i));
>> + print_generic_stmt (outf, SUB_ACCESS_FN (sub, 1), 0);
>> + dump_subscript (outf, sub);
>> }
>>
>> fprintf (outf, " inner loop index: %d\n", DDR_INNER_LOOP (ddr));
>> @@ -1484,11 +1499,10 @@ 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);
>> @@ -1506,82 +1520,217 @@ 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;
>> - }
>> - 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;
>> + DDR_ARE_DEPENDENT (res) = chrec_dont_know;
>> + return res;
>> + }
>> +
>> + /* For unconstrained bases, the outer (highest-index) 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 the outer subscript) so limit the search to the last real
>> + component access.
>> +
>> + E.g. for:
>>
>> - 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);
>> + void
>> + f (int a[][8], int b[][8])
>> + {
>> + for (int i = 0; i < 8; ++i)
>> + a[i * 2][0] = b[i][0];
>> }
>> - return res;
>> +
>> + 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;
>> +
>> + /* Now look for two sequences of component references that have the same
>> + type in both A and B. The first sequence includes an arbitrary mixture
>> + of array and structure references while the second always ends on a
>> + structure reference.
>> +
>> + The former (arbitrary) sequence uses access functions:
>> +
>> + [START_A, START_A + NUM_DIMENSIONS) of A
>> + [START_B, START_B + NUM_DIMENSIONS) of B
>> +
>> + The latter sequence uses access functions:
>> +
>> + [STRUCT_START_A, STRUCT_START_A + STRUCT_NUM_DIMENSIONS) of A
>> + [STRUCT_START_B, STRUCT_START_B + STRUCT_NUM_DIMENSIONS) of B
>> +
>> + STRUCT_REF_A and STRUCT_REF_B are the outer references for the
> IIUC, A and B always share the same latter sequence, and the common
> latter sequence ends at a structure reference providing alias
> information.
The A and B accesses aren't necessarily the same, they just have the
compatible types. E.g. for:
struct s { int x[8]; int y[8]; } *a, *b;
... a->x[0] = b->y[1] ...
the sequence would include:
a: [0] .x
b: [1] .y
> Is it possible to record the the former arbitrary
> references instead of simple flag DDR_COULD_BE_INDEPENDENT_P. With
> this information, alias check can be simplified by stripping away
> address computation for the shared common sub-sequence. I doubt
> vect_create_cond_for_alias_checks could detect this kind CSE for now.
> Ah, I see you changed alias check code generation in order to handle
> this.
The num_dimensions sequence is only used if it ends at the original
base and if the bases are equal. In other cases it doesn't really help.
The struct_num_dimensions sequence is meant to be the one that is
helpful even when the bases aren't equal.
Like you say, there's a follow-on patch that uses this for runtime
alias checking.
>> + latter sequence. */
>> + unsigned int start_a = 0;
>> + unsigned int start_b = 0;
>> + unsigned int num_dimensions = 0;
>> + unsigned int struct_start_a = 0;
>> + unsigned int struct_start_b = 0;
>> + unsigned int struct_num_dimensions = 0;
>> + unsigned int index_a = 0;
>> + unsigned int index_b = 0;
>> + tree next_ref_a = DR_REF (a);
>> + tree next_ref_b = DR_REF (b);
>> + tree struct_ref_a = NULL_TREE;
>> + tree struct_ref_b = NULL_TREE;
>> + while (index_a < num_dimensions_a && index_b < num_dimensions_b)
>> + {
>> + gcc_checking_assert (handled_component_p (next_ref_a));
>> + gcc_checking_assert (handled_component_p (next_ref_b));
>> + tree outer_ref_a = TREE_OPERAND (next_ref_a, 0);
>> + tree outer_ref_b = TREE_OPERAND (next_ref_b, 0);
>> + tree type_a = TREE_TYPE (outer_ref_a);
>> + tree type_b = TREE_TYPE (outer_ref_b);
>> + if (types_compatible_p (type_a, type_b))
>> + {
>> + /* This pair of accesses belong to a suitable sequence. */
>> + if (start_a + num_dimensions != index_a
>> + || start_b + num_dimensions != index_b)
>> + {
>> + /* Start a new sequence here. */
>> + start_a = index_a;
>> + start_b = index_b;
>> + num_dimensions = 0;
>> + }
>> + num_dimensions += 1;
>> + if (TREE_CODE (type_a) == RECORD_TYPE)
>> + {
>> + struct_start_a = start_a;
>> + struct_start_b = start_b;
>> + struct_num_dimensions = num_dimensions;
>> + struct_ref_a = outer_ref_a;
>> + struct_ref_b = outer_ref_b;
>> + }
>> + next_ref_a = outer_ref_a;
>> + next_ref_b = outer_ref_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)
>> + {
>> + index_a += 1;
>> + next_ref_a = outer_ref_a;
>> + }
>> + if (size_b <= size_a)
>> + {
>> + index_b += 1;
>> + next_ref_b = outer_ref_b;
>> + }
>> }
>>
>> - /* 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 the sequence 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 = (start_a + num_dimensions == num_dimensions_a
>> + && start_b + num_dimensions == 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))));
> Major change is in function initialize_data_dependence_relation in
> order to detect partial alias opportunity. The original equality
> check on DR_BASE_OBJECT is bypassed now. IMHO better to introduce a
> new parameter to compute_data_reference_for_loop etc., indicating
> whether we want to handle partial alias opportunity or not. After
> all, such computation is unnecessary for predcom/prefetch/parloop.
> It's only a waste of time computing it.
Well, it also means that we can now prove the accesses are independent
in more cases. E.g. previously we would assume the a and b accesses in:
struct s { int x[16]; } *a, *b;
for (int i = 0; i < 8; ++i)
a->x[i] = b->x[i + 8];
could conflict.
If callers don't need to know what the relationship between a and b is,
I think they should check for that before going through the process of
initialising and analysing the ddr.
>> +
>> + /* 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))
>> + num_dimensions += 1;
>> + }
>> + else
>> + {
>> + start_a = struct_start_a;
>> + start_b = struct_start_b;
>> + num_dimensions = struct_num_dimensions;
>> }
>>
>> - /* 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 (num_dimensions == 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 (struct_ref_a)
>> + || ref_contains_union_access_p (struct_ref_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 (num_dimensions);
>> 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 < num_dimensions; ++i)
>> {
>> struct subscript *subscript;
>>
>> subscript = XNEW (struct subscript);
>> + SUB_ACCESS_FN (subscript, 0) = DR_ACCESS_FN (a, start_a + i);
>> + SUB_ACCESS_FN (subscript, 1) = DR_ACCESS_FN (b, 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;
>> @@ -3163,14 +3312,15 @@ 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)
>> {
>> @@ -3188,8 +3338,8 @@ 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)
>> @@ -3249,10 +3399,11 @@ 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;
>> @@ -3315,10 +3466,11 @@ 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)
>> {
>> @@ -3330,7 +3482,7 @@ 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);
>> @@ -3401,6 +3553,23 @@ 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. */
>> @@ -3432,8 +3601,7 @@ 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. */
>> @@ -3466,12 +3634,11 @@ 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;
>> @@ -3507,12 +3674,10 @@ 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;
>>
>> @@ -3591,13 +3756,13 @@ 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;
>> @@ -3609,8 +3774,8 @@ 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);
>>
>> @@ -3659,7 +3824,7 @@ 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 2017-03-28 16:19:28.000000000 +0100
>> +++ gcc/tree-ssa-loop-prefetch.c 2017-05-03 08:48:48.737038502 +0100
>> @@ -1650,6 +1650,7 @@ 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
> As said, we could avoid computing such information in the first place.
> I can see predcom ingores it by explicitly checking DR_BASE_OBJECT,
> what about tree-parloops.c?
For parloops, it should help that we can now prove lack of dependence
in more cases.
Thanks,
Richard
