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Alternative check for vector refs with same alignment

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vect_find_same_alignment_drs uses the ddr dependence distance
to tell whether two references have the same alignment.  Although
that's safe with the current code, there's no particular reason
why a dependence distance of 0 should mean that the accesses start
on the same byte.  E.g. a reference to a full complex value could
in principle depend on a reference to the imaginary component.
A later patch adds support for this kind of dependence.

On the other side, checking modulo vf is pessimistic when the step
divided by the element size is a factor of 2.

This patch instead looks for cases in which the drs have the same
base, offset and step, and for which the difference in their constant
initial values is a multiple of the alignment.

2017-05-03  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-vect-data-refs.c (vect_find_same_alignment_drs): Remove
	loop_vinfo argument and use of dependence distance vectors.
	Check instead whether the two references differ only in their
	initial value and assume that they have the same alignment if the
	difference is a multiple of the vector alignment.
	(vect_analyze_data_refs_alignment): Update call accordingly.

gcc/testsuite/
	* gcc.dg/vect/vect-103.c: Update wording of dump message.

From-SVN: r248730
This commit is contained in:
Richard Sandiford 2017-05-31 12:05:10 +00:00 • committed by Richard Sandiford
parent c9f1615102
commit 748bbe7202
4 changed files with 42 additions and 48 deletions
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9
gcc/ChangeLog
View file

@ -1,3 +1,12 @@
2017-05-31 Richard Sandiford <richard.sandiford@linaro.org>
* tree-vect-data-refs.c (vect_find_same_alignment_drs): Remove
loop_vinfo argument and use of dependence distance vectors.
Check instead whether the two references differ only in their
initial value and assume that they have the same alignment if the
difference is a multiple of the vector alignment.
(vect_analyze_data_refs_alignment): Update call accordingly.
2017-05-31 Martin Liska <mliska@suse.cz>
PR target/79155

4
gcc/testsuite/ChangeLog
View file

@ -1,3 +1,7 @@
2017-05-31 Richard Sandiford <richard.sandiford@linaro.org>
* gcc.dg/vect/vect-103.c: Update wording of dump message.
2017-05-31 Bin Cheng <bin.cheng@arm.com>
* gcc.dg/vect/pr80815-3.c: New test.

2
gcc/testsuite/gcc.dg/vect/vect-103.c
View file

@ -55,5 +55,5 @@ int main (void)
}
/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
/* { dg-final { scan-tree-dump-times "dependence distance modulo vf == 0" 1 "vect" } } */
/* { dg-final { scan-tree-dump-times "accesses have the same alignment" 1 "vect" } } */

75
gcc/tree-vect-data-refs.c
View file

@ -2140,20 +2140,12 @@ vect_enhance_data_refs_alignment (loop_vec_info loop_vinfo)
vectorization factor. */
static void
vect_find_same_alignment_drs (struct data_dependence_relation *ddr,
loop_vec_info loop_vinfo)
vect_find_same_alignment_drs (struct data_dependence_relation *ddr)
{
unsigned int i;
struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
int vectorization_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
struct data_reference *dra = DDR_A (ddr);
struct data_reference *drb = DDR_B (ddr);
stmt_vec_info stmtinfo_a = vinfo_for_stmt (DR_STMT (dra));
stmt_vec_info stmtinfo_b = vinfo_for_stmt (DR_STMT (drb));
int dra_size = GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (DR_REF (dra))));
int drb_size = GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (DR_REF (drb))));
lambda_vector dist_v;
unsigned int loop_depth;
if (DDR_ARE_DEPENDENT (ddr) == chrec_known)
return;
@ -2161,48 +2153,37 @@ vect_find_same_alignment_drs (struct data_dependence_relation *ddr,
if (dra == drb)
return;
if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know)
if (!operand_equal_p (DR_BASE_OBJECT (dra), DR_BASE_OBJECT (drb),
OEP_ADDRESS_OF)
|| !operand_equal_p (DR_OFFSET (dra), DR_OFFSET (drb), 0)
|| !operand_equal_p (DR_STEP (dra), DR_STEP (drb), 0))
return;
/* Loop-based vectorization and known data dependence. */
if (DDR_NUM_DIST_VECTS (ddr) == 0)
return;
/* Data-dependence analysis reports a distance vector of zero
for data-references that overlap only in the first iteration
but have different sign step (see PR45764).
So as a sanity check require equal DR_STEP. */
if (!operand_equal_p (DR_STEP (dra), DR_STEP (drb), 0))
return;
loop_depth = index_in_loop_nest (loop->num, DDR_LOOP_NEST (ddr));
FOR_EACH_VEC_ELT (DDR_DIST_VECTS (ddr), i, dist_v)
/* Two references with distance zero have the same alignment. */
offset_int diff = (wi::to_offset (DR_INIT (dra))
- wi::to_offset (DR_INIT (drb)));
if (diff != 0)
{
int dist = dist_v[loop_depth];
/* Get the wider of the two alignments. */
unsigned int align_a = TYPE_ALIGN_UNIT (STMT_VINFO_VECTYPE (stmtinfo_a));
unsigned int align_b = TYPE_ALIGN_UNIT (STMT_VINFO_VECTYPE (stmtinfo_b));
unsigned int max_align = MAX (align_a, align_b);
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location,
"dependence distance = %d.\n", dist);
/* Require the gap to be a multiple of the larger vector alignment. */
if (!wi::multiple_of_p (diff, max_align, SIGNED))
return;
}
/* Same loop iteration. */
if (dist == 0
|| (dist % vectorization_factor == 0 && dra_size == drb_size))
{
/* Two references with distance zero have the same alignment. */
STMT_VINFO_SAME_ALIGN_REFS (stmtinfo_a).safe_push (drb);
STMT_VINFO_SAME_ALIGN_REFS (stmtinfo_b).safe_push (dra);
if (dump_enabled_p ())
{
dump_printf_loc (MSG_NOTE, vect_location,
"accesses have the same alignment.\n");
dump_printf (MSG_NOTE,
"dependence distance modulo vf == 0 between ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dra));
dump_printf (MSG_NOTE, " and ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (drb));
dump_printf (MSG_NOTE, "\n");
}
}
STMT_VINFO_SAME_ALIGN_REFS (stmtinfo_a).safe_push (drb);
STMT_VINFO_SAME_ALIGN_REFS (stmtinfo_b).safe_push (dra);
if (dump_enabled_p ())
{
dump_printf_loc (MSG_NOTE, vect_location,
"accesses have the same alignment: ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (dra));
dump_printf (MSG_NOTE, " and ");
dump_generic_expr (MSG_NOTE, TDF_SLIM, DR_REF (drb));
dump_printf (MSG_NOTE, "\n");
}
}
@ -2226,7 +2207,7 @@ vect_analyze_data_refs_alignment (loop_vec_info vinfo)
unsigned int i;
FOR_EACH_VEC_ELT (ddrs, i, ddr)
vect_find_same_alignment_drs (ddr, vinfo);
vect_find_same_alignment_drs (ddr);
vec<data_reference_p> datarefs = vinfo->datarefs;
struct data_reference *dr;