[PATCH] PR/67682, break SLP groups up if only some elements match
Richard Biener
richard.guenther@gmail.com
Tue Nov 10 12:51:00 GMT 2015
On Tue, Nov 10, 2015 at 1:45 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On Mon, Nov 9, 2015 at 3:59 PM, Alan Lawrence <alan.lawrence@arm.com> wrote:
>> On 06/11/15 12:55, Richard Biener wrote:
>>>
>>>> + /* GROUP_GAP of the first group now has to skip over the second group too. */
>>>> + GROUP_GAP (first_vinfo) += group2_size;
>>>
>>> Please add a MSG_NOTE debug printf stating that we split the group and
>>> at which element.
>>
>> Done.
>>
>>> I think you want to add && STMT_VINFO_GROUPED_ACCESS (vinfo_for_stmt (stmt))
>>> otherwise this could be SLP reductions where there is no way the split
>>> group would enable vectorization.
>>
>> Ah, I had thought that the (GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt))) check
>> sufficed for that, as per e.g. the section above
>> /* Create a node (a root of the SLP tree) for the packed grouped stores. */
>> But done.
>>
>>> Note that BB vectorization now also very aggressively falls back to considering
>>> non-matches being "external".
>>>
>>> Not sure why that doesn't trigger for your testcases ;)
>>
>> I tested against trunk r229944, on which all of my scan-tree-dump's were failing....
>>
>>> I'm comfortable with the i < group_size half of the patch. For the other piece
>>> I'd like to see more compile-time / success data from, say, building
>>> SPEC CPU 2006.
>>
>> Well, as a couple of quick data points, a compile of SPEC2000 on
>> aarch64-none-linux-gnu (-Ofast -fomit-frame-pointer -mcpu=cortex-a57), I have:
>>
>> 3080 successes without patch;
>> +79 successes from the "i < vectorization_factor" part of the patch (on its own)
>> +90 successes from the (i>=vectorization_factor) && "i < group_size" part (on its own)
>> +(79 from first) +(90 from second) + (an additional 62) from both parts together.
>>
>> And for SPEC2006, aarch64-linux-gnu (-O3 -fomit-frame-pointer -mcpu=cortex-a57):
>> 11979 successes without patch;
>> + 499 from the "i < vectorization_factor" part
>> + 264 from the (i >= vectorization factor) && (i < group_size)" part
>> + extra 336 if both parts combined.
>
> Thanks
>
>> I haven't done any significant measurements of compile-time yet.
>>
>> (snipping this bit out-of-order)
>>> Hmm. This is of course pretty bad for compile-time for the non-matching
>>> case as that effectively will always split into N pieces if we feed it
>>> garbage (that is, without being sure that at least one pice _will_ vectorize).
>>>
>>> OTOH with the current way of computing "matches" we'd restrict ourselves
>>> to cases where the first stmt we look at (and match to) happens to be
>>> the operation that in the end will form a matching group.
>> ...
>>> Eventually we'd want to improve the "matches" return
>>> to include the affected stmts (ok, that'll be not very easy) so we can do
>>> a cheap "if we split here will it fix that particular mismatch" check.
>>
>> Yes, I think there are a bunch of things we can do here, that would be more
>> powerful than the simple approach I used here. The biggest limiting factor will
>> probably be (lack of) permutation, i.e. if we only SLP stores to consecutive
>> addresses.
>
> Yeah, doing anything else requires us to use masked or strided stores though.
>
>>> So, please split the patch and I suggest to leave the controversical part
>>> for next stage1 together with some improvement on the SLP build process
>>> itself?
>>
>> Here's a reduced version with just the second case,
>> bootstrapped+check-gcc/g++ on x86_64.
>>
>> gcc/ChangeLog:
>>
>> * tree-vect-slp.c (vect_split_slp_store_group): New.
>> (vect_analyze_slp_instance): During basic block SLP, recurse on
>> subgroups if vect_build_slp_tree fails after 1st vector.
>>
>> gcc/testsuite/ChangeLog:
>>
>> * gcc.dg/vect/bb-slp-7.c (main1): Make subgroups non-isomorphic.
>> * gcc.dg/vect/bb-slp-subgroups-1.c: New.
>> * gcc.dg/vect/bb-slp-subgroups-2.c: New.
>> * gcc.dg/vect/bb-slp-subgroups-3.c: New.
>> * gcc.dg/vect/bb-slp-subgroups-4.c: New.
>> ---
>> gcc/testsuite/gcc.dg/vect/bb-slp-7.c | 10 ++--
>> gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-1.c | 44 +++++++++++++++
>> gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-2.c | 42 +++++++++++++++
>> gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-3.c | 41 ++++++++++++++
>> gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-4.c | 41 ++++++++++++++
>> gcc/tree-vect-slp.c | 74 +++++++++++++++++++++++++-
>> 6 files changed, 246 insertions(+), 6 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-1.c
>> create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-2.c
>> create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-3.c
>> create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-4.c
>>
>> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-7.c b/gcc/testsuite/gcc.dg/vect/bb-slp-7.c
>> index ab54a48..b8bef8c 100644
>> --- a/gcc/testsuite/gcc.dg/vect/bb-slp-7.c
>> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-7.c
>> @@ -16,12 +16,12 @@ main1 (unsigned int x, unsigned int y)
>> unsigned int *pout = &out[0];
>> unsigned int a0, a1, a2, a3;
>>
>> - /* Non isomorphic. */
>> + /* Non isomorphic, even 64-bit subgroups. */
>> a0 = *pin++ + 23;
>> - a1 = *pin++ + 142;
>> + a1 = *pin++ * 142;
>> a2 = *pin++ + 2;
>> a3 = *pin++ * 31;
>> -
>> +
>> *pout++ = a0 * x;
>> *pout++ = a1 * y;
>> *pout++ = a2 * x;
>> @@ -29,7 +29,7 @@ main1 (unsigned int x, unsigned int y)
>>
>> /* Check results. */
>> if (out[0] != (in[0] + 23) * x
>> - || out[1] != (in[1] + 142) * y
>> + || out[1] != (in[1] * 142) * y
>> || out[2] != (in[2] + 2) * x
>> || out[3] != (in[3] * 31) * y)
>> abort();
>> @@ -47,4 +47,4 @@ int main (void)
>> }
>>
>> /* { dg-final { scan-tree-dump-times "basic block vectorized" 0 "slp2" } } */
>> -
>> +
>> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-1.c b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-1.c
>> new file mode 100644
>> index 0000000..39c23c3
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-1.c
>> @@ -0,0 +1,44 @@
>> +/* { dg-require-effective-target vect_int } */
>> +/* PR tree-optimization/67682. */
>> +
>> +#include "tree-vect.h"
>> +
>> +int __attribute__((__aligned__(8))) a[8];
>> +int __attribute__((__aligned__(8))) b[4];
>> +
>> +__attribute__ ((noinline)) void
>> +test ()
>> +{
>> + a[0] = b[0];
>> + a[1] = b[1];
>> + a[2] = b[2];
>> + a[3] = b[3];
>> + a[4] = 0;
>> + a[5] = 0;
>> + a[6] = 0;
>> + a[7] = 0;
>> +}
>> +
>> +int
>> +main (int argc, char **argv)
>> +{
>> + check_vect ();
>> +
>> + for (int i = 0; i < 8; i++)
>> + a[i] = 1;
>> + for (int i = 0; i < 4; i++)
>> + b[i] = i + 4;
>> + __asm__ volatile ("" : : : "memory");
>> + test (a, b);
>> + __asm__ volatile ("" : : : "memory");
>> + for (int i = 0; i < 4; i++)
>> + if (a[i] != i+4)
>> + abort ();
>> + for (int i = 4; i < 8; i++)
>> + if (a[i] != 0)
>> + abort ();
>> + return 0;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "Basic block will be vectorized using SLP" 1 "slp2" } } */
>> +/* { dg-final { scan-tree-dump-times "basic block vectorized" 1 "slp2" } } */
>> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-2.c b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-2.c
>> new file mode 100644
>> index 0000000..06099fd
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-2.c
>> @@ -0,0 +1,42 @@
>> +/* { dg-require-effective-target vect_int } */
>> +/* PR tree-optimization/67682. */
>> +
>> +#include "tree-vect.h"
>> +
>> +int __attribute__((__aligned__(8))) a[8];
>> +int __attribute__((__aligned__(8))) b[8];
>> +
>> +__attribute__ ((noinline)) void
>> +test ()
>> +{
>> + a[0] = b[0];
>> + a[1] = b[1] + 1;
>> + a[2] = b[2] * 2;
>> + a[3] = b[3] + 3;
>> +
>> + a[4] = b[4] + 4;
>> + a[5] = b[5] + 4;
>> + a[6] = b[6] + 4;
>> + a[7] = b[7] + 4;
>> +}
>> +
>> +int
>> +main (int argc, char **argv)
>> +{
>> + check_vect ();
>> +
>> + for (int i = 0; i < 8; i++)
>> + b[i] = i + 1;
>> + __asm__ volatile ("" : : : "memory");
>> + test (a, b);
>> + __asm__ volatile ("" : : : "memory");
>> + if ((a[0] != 1) || (a[1] != 3) || (a[2] != 6) || (a[3] != 7))
>> + abort ();
>> + for (int i = 4; i < 8; i++)
>> + if (a[i] != i + 5)
>> + abort ();
>> + return 0;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "Basic block will be vectorized using SLP" 1 "slp2" } } */
>> +/* { dg-final { scan-tree-dump-times "basic block vectorized" 1 "slp2" } } */
>> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-3.c b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-3.c
>> new file mode 100644
>> index 0000000..13c51f3
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-3.c
>> @@ -0,0 +1,41 @@
>> +/* { dg-require-effective-target vect_int } */
>> +/* PR tree-optimization/67682. */
>> +
>> +#include "tree-vect.h"
>> +
>> +int __attribute__((__aligned__(8))) a[8];
>> +int __attribute__((__aligned__(8))) b[4];
>> +
>> +__attribute__ ((noinline)) void
>> +test ()
>> +{
>> + a[0] = b[2] + 1;
>> + a[1] = b[0] + 2;
>> + a[2] = b[1] + 3;
>> + a[3] = b[1] + 4;
>> + a[4] = b[3] * 3;
>> + a[5] = b[0] * 4;
>> + a[6] = b[2] * 5;
>> + a[7] = b[1] * 7;
>> +}
>> +
>> +int
>> +main (int argc, char **argv)
>> +{
>> + check_vect ();
>> +
>> + for (int i = 0; i < 8; i++)
>> + a[i] = 1;
>> + for (int i = 0; i < 4; i++)
>> + b[i] = i + 4;
>> + __asm__ volatile ("" : : : "memory");
>> + test (a, b);
>> + __asm__ volatile ("" : : : "memory");
>> + if ((a[0] != 7) || a[1] != 6 || (a[2] != 8) || (a[3] != 9)
>> + || (a[4] != 21) || (a[5] != 16) || (a[6] != 30) || (a[7] != 35))
>> + abort ();
>> + return 0;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "Basic block will be vectorized using SLP" 1 "slp2" } } */
>> +/* { dg-final { scan-tree-dump-times "basic block vectorized" 1 "slp2" } } */
>> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-4.c b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-4.c
>> new file mode 100644
>> index 0000000..6ae9a89
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-subgroups-4.c
>> @@ -0,0 +1,41 @@
>> +/* { dg-require-effective-target vect_int } */
>> +/* PR tree-optimization/67682. */
>> +
>> +#include "tree-vect.h"
>> +
>> +int __attribute__((__aligned__(8))) a[8];
>> +int __attribute__((__aligned__(8))) b[8];
>> +
>> +__attribute__ ((noinline)) void
>> +test ()
>> +{
>> + a[0] = b[0] + 1;
>> + a[1] = b[1] + 2;
>> + a[2] = b[2] + 3;
>> + a[3] = b[3] + 4;
>> + a[4] = b[0] * 3;
>> + a[5] = b[2] * 4;
>> + a[6] = b[4] * 5;
>> + a[7] = b[6] * 7;
>> +}
>> +
>> +int
>> +main (int argc, char **argv)
>> +{
>> + check_vect ();
>> +
>> + for (int i = 0; i < 8; i++)
>> + a[i] = 1;
>> + for (int i = 0; i < 8; i++)
>> + b[i] = i + 4;
>> + __asm__ volatile ("" : : : "memory");
>> + test (a, b);
>> + __asm__ volatile ("" : : : "memory");
>> + if ((a[0] != 5) || (a[1] != 7) || (a[2] != 9) || (a[3] != 11)
>> + || (a[4] != 12) || (a[5] != 24) || (a[6] != 40) || (a[7] != 70))
>> + abort ();
>> + return 0;
>> +}
>> +
>> +/* { dg-final { scan-tree-dump-times "Basic block will be vectorized using SLP" 1 "slp2" } } */
>> +/* { dg-final { scan-tree-dump-times "basic block vectorized" 1 "slp2" } } */
>> diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
>> index cfdfc29..05d4b35 100644
>> --- a/gcc/tree-vect-slp.c
>> +++ b/gcc/tree-vect-slp.c
>> @@ -1606,6 +1606,54 @@ vect_analyze_slp_cost (slp_instance instance, void *data)
>> body_cost_vec.release ();
>> }
>>
>> +/* Splits a group of stores, currently beginning at FIRST_STMT, into two groups:
>> + one (still beginning at FIRST_STMT) of size GROUP1_SIZE (also containing
>> + the first GROUP1_SIZE stmts, since stores are consecutive), the second
>> + containing the remainder.
>> + Return the first stmt in the second group. */
>> +
>> +static gimple *
>> +vect_split_slp_store_group (gimple *first_stmt, unsigned group1_size)
>> +{
>> + stmt_vec_info first_vinfo = vinfo_for_stmt (first_stmt);
>> + gcc_assert (GROUP_FIRST_ELEMENT (first_vinfo) == first_stmt);
>> + gcc_assert (group1_size > 0);
>> + int group2_size = GROUP_SIZE (first_vinfo) - group1_size;
>> + gcc_assert (group2_size > 0);
>> + GROUP_SIZE (first_vinfo) = group1_size;
>> +
>> + gimple *stmt = first_stmt;
>> + for (unsigned i = group1_size; i > 1; i--)
>> + {
>> + stmt = GROUP_NEXT_ELEMENT (vinfo_for_stmt (stmt));
>> + gcc_assert (GROUP_GAP (vinfo_for_stmt (stmt)) == 1);
>> + }
>> + /* STMT is now the last element of the first group. */
>> + gimple *group2 = GROUP_NEXT_ELEMENT (vinfo_for_stmt (stmt));
>> + GROUP_NEXT_ELEMENT (vinfo_for_stmt (stmt)) = 0;
>> +
>> + GROUP_SIZE (vinfo_for_stmt (group2)) = group2_size;
>> + for (stmt = group2; stmt; stmt = GROUP_NEXT_ELEMENT (vinfo_for_stmt (stmt)))
>> + {
>> + GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt)) = group2;
>> + gcc_assert (GROUP_GAP (vinfo_for_stmt (stmt)) == 1);
>> + }
>> +
>> + /* For the second group, the GROUP_GAP is that before the original group,
>> + plus skipping over the first vector. */
>> + GROUP_GAP (vinfo_for_stmt (group2)) =
>> + GROUP_GAP (first_vinfo) + group1_size;
>> +
>> + /* GROUP_GAP of the first group now has to skip over the second group too. */
>> + GROUP_GAP (first_vinfo) += group2_size;
>> +
>> + if (dump_enabled_p ())
>> + dump_printf_loc (MSG_NOTE, vect_location, "Split group into %d and %d\n",
>> + group1_size, group2_size);
>> +
>> + return group2;
>> +}
>> +
>> /* Analyze an SLP instance starting from a group of grouped stores. Call
>> vect_build_slp_tree to build a tree of packed stmts if possible.
>> Return FALSE if it's impossible to SLP any stmt in the loop. */
>> @@ -1621,7 +1669,7 @@ vect_analyze_slp_instance (vec_info *vinfo,
>> tree vectype, scalar_type = NULL_TREE;
>> gimple *next;
>> unsigned int vectorization_factor = 0;
>> - int i;
>> + unsigned int i;
>> unsigned int max_nunits = 0;
>> vec<slp_tree> loads;
>> struct data_reference *dr = STMT_VINFO_DATA_REF (vinfo_for_stmt (stmt));
>> @@ -1811,6 +1859,30 @@ vect_analyze_slp_instance (vec_info *vinfo,
>> vect_free_slp_tree (node);
>> loads.release ();
>>
>> + /* For basic block SLP, try to break the group up into multiples of the
>> + vectorization factor. */
>> + if (is_a <bb_vec_info> (vinfo)
>> + && GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt))
>> + && STMT_VINFO_GROUPED_ACCESS (vinfo_for_stmt (stmt)))
>> + {
>> + /* We consider breaking the group only on VF boundaries from the existing
>> + start. */
>> + for (i = 0; i < group_size; i++)
>> + if (!matches[i]) break;
>> +
>> + if (i >= vectorization_factor && i < group_size)
>> + {
>> + /* Split into two groups at the first vector boundary before i. */
>> + gcc_assert ((vectorization_factor & (vectorization_factor - 1)) == 0);
>
> Just noticing this... if we have a vectorization factor of 4 and matches
> is 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0 then this will split into 1, 1, 1, 1 and
> 1, 1, 0, 0, 0, ... where we know from the matches that it will again fail?
>
> Thus shouldn't we split either only if i % vectorization_factor is 0 or
> if not, split "twice", dropping the intermediate surely non-matching
> group of vectorization_factor size? After all if we split like with the
> patch then the upper half will _not_ be splitted again with the
> simplified patch (result will be 1, 1, 0, 0, 0, 0, 0, 0 again).
>
> So I expect that the statistics will be the same if we restrict splitting
> to the i % vectorization_factor == 0 case, or rather split where we do
> now but only re-analyze group2 if i % vectorization_factor == 0 holds?
>
> Ok with that change. Improvements on that incrementally.
Btw, it just occurs to me that the whole thing is equivalent to splitting
the store-group into vector-size pieces up-front? That way we do
the maximum splitting up-frond and avoid any redundant work?
The patch is still ok as said, just the above may be a simple thing
to explore.
Thanks,
Richard.
> Thanks,
> Richard.
>
>> + i &= ~(vectorization_factor - 1);
>> + gimple *grp2start = vect_split_slp_store_group (stmt, i);
>> + return vect_analyze_slp_instance (vinfo, stmt, max_tree_size)
>> + | vect_analyze_slp_instance (vinfo, grp2start, max_tree_size);
>> + }
>> + /* Even though the first vector did not all match, we might be able to SLP
>> + (some) of the remainder. FORNOW ignore this possibility. */
>> + }
>> +
>> return false;
>> }
>>
>> --
>> 1.9.1
>>
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