on 2023/5/23 14:19, Richard Biener wrote:
> On Tue, May 23, 2023 at 5:01 AM Kewen.Lin <li...@linux.ibm.com> wrote:
>>
>> Hi Richi,
>>
>> Thanks for the review!
>>
>> on 2023/5/22 21:44, Richard Biener wrote:
>>> On Wed, May 17, 2023 at 8:15 AM Kewen.Lin <li...@linux.ibm.com> wrote:
>>>>
>>>> Hi,
>>>>
>>>> Following Richi's suggestion in [1], I'm working on deferring
>>>> cost evaluation next to the transformation, this patch is
>>>> to enhance function vect_transform_slp_perm_load_1 which
>>>> could under-cost for vector permutation, since the costing
>>>> doesn't try to consider nvectors_per_build, it's inconsistent
>>>> with the transformation part.
>>>>
>>>> Bootstrapped and regtested on x86_64-redhat-linux,
>>>> aarch64-linux-gnu and powerpc64{,le}-linux-gnu.
>>>>
>>>> Is it ok for trunk?
>>>>
>>>> [1] https://gcc.gnu.org/pipermail/gcc-patches/2021-January/563624.html
>>>>
>>>> BR,
>>>> Kewen
>>>> -----
>>>> gcc/ChangeLog:
>>>>
>>>> * tree-vect-slp.cc (vect_transform_slp_perm_load_1): Adjust the
>>>> calculation on n_perms by considering nvectors_per_build.
>>>>
>>>> gcc/testsuite/ChangeLog:
>>>>
>>>> * gcc.dg/vect/costmodel/ppc/costmodel-slp-perm.c: New test.
>>>> ---
>>>> .../vect/costmodel/ppc/costmodel-slp-perm.c | 23 +++++++
>>>> gcc/tree-vect-slp.cc | 66 ++++++++++---------
>>>> 2 files changed, 57 insertions(+), 32 deletions(-)
>>>> create mode 100644
>>>> gcc/testsuite/gcc.dg/vect/costmodel/ppc/costmodel-slp-perm.c
>>>>
>>>> diff --git a/gcc/testsuite/gcc.dg/vect/costmodel/ppc/costmodel-slp-perm.c
>>>> b/gcc/testsuite/gcc.dg/vect/costmodel/ppc/costmodel-slp-perm.c
>>>> new file mode 100644
>>>> index 00000000000..e5c4dceddfb
>>>> --- /dev/null
>>>> +++ b/gcc/testsuite/gcc.dg/vect/costmodel/ppc/costmodel-slp-perm.c
>>>> @@ -0,0 +1,23 @@
>>>> +/* { dg-do compile } */
>>>> +/* { dg-require-effective-target vect_int } */
>>>> +/* { dg-require-effective-target powerpc_p9vector_ok } */
>>>> +/* Specify power9 to ensure the vectorization is profitable
>>>> + and test point stands, otherwise it could be not profitable
>>>> + to vectorize. */
>>>> +/* { dg-additional-options "-mdejagnu-cpu=power9 -mpower9-vector" } */
>>>> +
>>>> +/* Verify we cost the exact count for required vec_perm. */
>>>> +
>>>> +int x[1024], y[1024];
>>>> +
>>>> +void
>>>> +foo ()
>>>> +{
>>>> + for (int i = 0; i < 512; ++i)
>>>> + {
>>>> + x[2 * i] = y[1023 - (2 * i)];
>>>> + x[2 * i + 1] = y[1023 - (2 * i + 1)];
>>>> + }
>>>> +}
>>>> +
>>>> +/* { dg-final { scan-tree-dump-times "2 times vec_perm" 1 "vect" } } */
>>>> diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
>>>> index e5c9d7e766e..af9a6dd4fa9 100644
>>>> --- a/gcc/tree-vect-slp.cc
>>>> +++ b/gcc/tree-vect-slp.cc
>>>> @@ -8115,12 +8115,12 @@ vect_transform_slp_perm_load_1 (vec_info *vinfo,
>>>> slp_tree node,
>>>>
>>>> mode = TYPE_MODE (vectype);
>>>> poly_uint64 nunits = TYPE_VECTOR_SUBPARTS (vectype);
>>>> + unsigned int nstmts = SLP_TREE_NUMBER_OF_VEC_STMTS (node);
>>>>
>>>> /* Initialize the vect stmts of NODE to properly insert the generated
>>>> stmts later. */
>>>> if (! analyze_only)
>>>> - for (unsigned i = SLP_TREE_VEC_STMTS (node).length ();
>>>> - i < SLP_TREE_NUMBER_OF_VEC_STMTS (node); i++)
>>>> + for (unsigned i = SLP_TREE_VEC_STMTS (node).length (); i < nstmts;
>>>> i++)
>>>> SLP_TREE_VEC_STMTS (node).quick_push (NULL);
>>>>
>>>> /* Generate permutation masks for every NODE. Number of masks for each
>>>> NODE
>>>> @@ -8161,7 +8161,10 @@ vect_transform_slp_perm_load_1 (vec_info *vinfo,
>>>> slp_tree node,
>>>> (b) the permutes only need a single vector input. */
>>>> mask.new_vector (nunits, group_size, 3);
>>>> nelts_to_build = mask.encoded_nelts ();
>>>> - nvectors_per_build = SLP_TREE_VEC_STMTS (node).length ();
>>>> + /* It's possible to obtain zero nstmts during analyze_only, so make
>>>> + it at least one to ensure the later computation for n_perms
>>>> + proceed. */
>>>> + nvectors_per_build = nstmts > 0 ? nstmts : 1;
>>>> in_nlanes = DR_GROUP_SIZE (stmt_info) * 3;
>>>> }
>>>> else
>>>> @@ -8252,40 +8255,39 @@ vect_transform_slp_perm_load_1 (vec_info *vinfo,
>>>> slp_tree node,
>>>> return false;
>>>> }
>>>>
>>>> - ++*n_perms;
>>>> -
>>>> + tree mask_vec = NULL_TREE;
>>>> if (!analyze_only)
>>>> - {
>>>> - tree mask_vec = vect_gen_perm_mask_checked (vectype,
>>>> indices);
>>>> + mask_vec = vect_gen_perm_mask_checked (vectype, indices);
>>>>
>>>> - if (second_vec_index == -1)
>>>> - second_vec_index = first_vec_index;
>>>> + if (second_vec_index == -1)
>>>> + second_vec_index = first_vec_index;
>>>>
>>>> - for (unsigned int ri = 0; ri < nvectors_per_build; ++ri)
>>>> + for (unsigned int ri = 0; ri < nvectors_per_build; ++ri)
>>>> + {
>>>> + ++*n_perms;
>>>
>>> So the "real" change is doing
>>>
>>> *n_perms += nvectors_per_build;
>>>
>>> and *n_perms was unused when !analyze_only? And since at
>>
>> Yes, although both !analyze_only and analyze_only calls pass n_perms in, now
>> only the call sites with analyze_only will use the returned n_perms further.
>>
>>> analysis time we (sometimes?) have zero nvectors you have to
>>> fixup above? Which cases are that?
>>
>> Yes, the fixup is to avoid to result in unexpected n_perms in function
>> vect_optimize_slp_pass::internal_node_cost。 One typical case is
>> gcc.dg/vect/bb-slp-50.c, without special casing zero, slp2 fails to optimize
>> out one more vec_perm unexpectedly.
>>
>> In vect_optimize_slp_pass::internal_node_cost, it checks if the returned
>> n_perms
>> is zero or not (vec_perm not needed or needed).
>>
>> if (!vect_transform_slp_perm_load_1 (m_vinfo, node, tmp_perm, vNULL,
>> nullptr, vf, true, false,
>> &n_perms))
>> {
>> auto rep = SLP_TREE_REPRESENTATIVE (node);
>> if (out_layout_i == 0)
>> {
>> /* Use the fallback cost if the load is an N-to-N permutation.
>> Otherwise assume that the node will be rejected later
>> and rebuilt from scalars. */
>> if (STMT_VINFO_GROUPED_ACCESS (rep)
>> && (DR_GROUP_SIZE (DR_GROUP_FIRST_ELEMENT (rep))
>> == SLP_TREE_LANES (node)))
>> return fallback_cost;
>> return 0;
>> }
>> return -1;
>> }
>>
>> /* See the comment above the corresponding VEC_PERM_EXPR handling. */
>> return n_perms == 0 ? 0 : 1;
>>
>> In vect_optimize_slp_pass::forward_pass (), it only considers the case that
>> factor > 0 (there is some vec_perm needed).
>>
>> /* Accumulate the cost of using LAYOUT_I within NODE,
>> both for the inputs and the outputs. */
>> int factor = internal_node_cost (vertex.node, layout_i,
>> layout_i);
>> if (factor < 0)
>> {
>> is_possible = false;
>> break;
>> }
>> else if (factor)
>> layout_costs.internal_cost.add_serial_cost
>> ({ vertex.weight * factor, m_optimize_size });
>
> Ah, OK - thanks for clarifying.
>
> The patch is OK.
Thanks! Committed in r14-1151.
BR,
Kewen
