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 });
BR,
Kewen
>
> In principle the patch looks good to me.
>
> Richard.
>
>> + if (analyze_only)
>> + continue;
>> + /* Generate the permute statement if necessary. */
>> + tree first_vec = dr_chain[first_vec_index + ri];
>> + tree second_vec = dr_chain[second_vec_index + ri];
>> + gassign *stmt = as_a<gassign *> (stmt_info->stmt);
>> + tree perm_dest
>> + = vect_create_destination_var (gimple_assign_lhs (stmt),
>> + vectype);
>> + perm_dest = make_ssa_name (perm_dest);
>> + gimple *perm_stmt
>> + = gimple_build_assign (perm_dest, VEC_PERM_EXPR,
>> first_vec,
>> + second_vec, mask_vec);
>> + vect_finish_stmt_generation (vinfo, stmt_info, perm_stmt,
>> + gsi);
>> + if (dce_chain)
>> {
>> - /* Generate the permute statement if necessary. */
>> - tree first_vec = dr_chain[first_vec_index + ri];
>> - tree second_vec = dr_chain[second_vec_index + ri];
>> - gassign *stmt = as_a<gassign *> (stmt_info->stmt);
>> - tree perm_dest
>> - = vect_create_destination_var (gimple_assign_lhs
>> (stmt),
>> - vectype);
>> - perm_dest = make_ssa_name (perm_dest);
>> - gimple *perm_stmt
>> - = gimple_build_assign (perm_dest, VEC_PERM_EXPR,
>> - first_vec, second_vec,
>> mask_vec);
>> - vect_finish_stmt_generation (vinfo, stmt_info,
>> perm_stmt,
>> - gsi);
>> - if (dce_chain)
>> - {
>> - bitmap_set_bit (used_defs, first_vec_index + ri);
>> - bitmap_set_bit (used_defs, second_vec_index + ri);
>> - }
>> -
>> - /* Store the vector statement in NODE. */
>> - SLP_TREE_VEC_STMTS (node) [vect_stmts_counter++]
>> - = perm_stmt;
>> + bitmap_set_bit (used_defs, first_vec_index + ri);
>> + bitmap_set_bit (used_defs, second_vec_index + ri);
>> }
>> +
>> + /* Store the vector statement in NODE. */
>> + SLP_TREE_VEC_STMTS (node)[vect_stmts_counter++] =
>> perm_stmt;
>> }
>> }
>> else if (!analyze_only)
>> --
>> 2.39.1
