Make the vectoriser drop to strided accesses for stores with gaps
We could vectorise:
for (...)
{
a[0] = ...;
a[1] = ...;
a[2] = ...;
a[3] = ...;
a += stride;
}
(including the case when stride == 8) but not:
for (...)
{
a[0] = ...;
a[1] = ...;
a[2] = ...;
a[3] = ...;
a += 8;
}
(where the stride is always 8). The former was treated as a "grouped
and strided" store, while the latter was treated as a grouped store
with gaps, which we don't support.
This patch makes us treat groups of stores with gaps at the end as
strided groups too. I tried to go through all uses of STMT_VINFO_STRIDED_P
and all vector uses of DR_STEP to see whether there were any hard-baked
assumptions, but couldn't see any. I wondered whether we should relax:
/* We do not have to consider dependences between accesses that belong
to the same group, unless the stride could be smaller than the
group size. */
if (DR_GROUP_FIRST_ELEMENT (stmtinfo_a)
&& (DR_GROUP_FIRST_ELEMENT (stmtinfo_a)
== DR_GROUP_FIRST_ELEMENT (stmtinfo_b))
&& !STMT_VINFO_STRIDED_P (stmtinfo_a))
return false;
for cases in which the step is constant and the absolute step is known
to be greater than the group size, but data dependence analysis should
already return chrec_known for those cases.
The new test is a version of vect-avg-15.c with the variable step
replaced by a constant one.
A natural follow-on would be to do the same for groups with gaps in
the middle:
/* Check that the distance between two accesses is equal to the type
size. Otherwise, we have gaps. */
diff = (TREE_INT_CST_LOW (DR_INIT (data_ref))
- TREE_INT_CST_LOW (prev_init)) / type_size;
if (diff != 1)
{
[...]
if (DR_IS_WRITE (data_ref))
{
if (dump_enabled_p ())
dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
"interleaved store with gaps\n");
return false;
}
But I think we should do that separately and see what the fallout
from this change is first.
2018-08-22 Richard Sandiford <richard.sandiford@arm.com>
gcc/
* tree-vect-data-refs.c (vect_analyze_group_access_1): Convert
grouped stores with gaps to a strided group.
gcc/testsuite/
* gcc.dg/vect/vect-avg-16.c: New test.
* gcc.dg/vect/slp-37.c: Expect the loop to be vectorized.
* gcc.dg/vect/vect-strided-u8-i8-gap4.c,
* gcc.dg/vect/vect-strided-u8-i8-gap4-big-array.c: Likewise for
the second loop in main1.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263772 138bc75d-0d04-0410-961f-82ee72b054a4