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Re: Handle data dependence relations with different bases
- From: Richard Sandiford <richard dot sandiford at linaro dot org>
- To: gcc-patches at gcc dot gnu dot org
- Cc: Richard Biener <richard dot guenther at gmail dot com>
- Date: Thu, 27 Jul 2017 13:19:56 +0100
- Subject: Re: Handle data dependence relations with different bases
- Authentication-results: sourceware.org; auth=none
- References: <87tw52s73r.fsf@linaro.org> <CAFiYyc0MREgfp6GCL6=d1hkRaEVX8NOAaX=hNgaGooEs8L5QbQ@mail.gmail.com> <87lgp38p59.fsf@linaro.org> <3947361.mLME8MOua7@polaris> <87y3s08hy2.fsf@linaro.org>
Richard Sandiford <richard.sandiford@linaro.org> writes:
> Eric Botcazou <ebotcazou@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.sandiford@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?
Thanks,
Richard
2017-07-27 Richard Sandiford <richard.sandiford@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" } } */