The following avoids splitting store dataref groups during SLP
discovery but instead forces (eventually single-lane) consecutive
lane SLP discovery for all lanes of the group, creating VEC_PERM
SLP nodes merging them so the store will always cover the whole group.
With this for example
int x[1024], y[1024], z[1024], w[1024];
void foo (void)
{
for (int i = 0; i < 256; i++)
{
x[4*i+0] = y[2*i+0];
x[4*i+1] = y[2*i+1];
x[4*i+2] = z[i];
x[4*i+3] = w[i];
}
}
which was previously using hybrid SLP can now be fully SLPed and
SSE code generated looks better (but of course you never know,
I didn't actually benchmark). We of course need a VF of four here.
.L2:
movdqa z(%rax), %xmm0
movdqa w(%rax), %xmm4
movdqa y(%rax,%rax), %xmm2
movdqa y+16(%rax,%rax), %xmm1
movdqa %xmm0, %xmm3
punpckhdq %xmm4, %xmm0
punpckldq %xmm4, %xmm3
movdqa %xmm2, %xmm4
shufps $238, %xmm3, %xmm2
movaps %xmm2, x+16(,%rax,4)
movdqa %xmm1, %xmm2
shufps $68, %xmm3, %xmm4
shufps $68, %xmm0, %xmm2
movaps %xmm4, x(,%rax,4)
shufps $238, %xmm0, %xmm1
movaps %xmm2, x+32(,%rax,4)
movaps %xmm1, x+48(,%rax,4)
addq $16, %rax
cmpq $1024, %rax
jne .L2
The extra permute nodes merging distinct branches of the SLP
tree might be unexpected for some code, esp. since
SLP_TREE_REPRESENTATIVE cannot be meaningfully set and we
cannot populate SLP_TREE_SCALAR_STMTS or SLP_TREE_SCALAR_OPS
consistently as we can have a mix of both.
The patch keeps the sub-trees form consecutive lanes but that's
in principle not necessary if we for example have an even/odd
split which now would result in N single-lane sub-trees. That's
left for future improvements.
The interesting part is how VLA vector ISAs handle merging of
two vectors that's not trivial even/odd merging. The strathegy
of how to build the permute tree might need adjustments for that
(in the end splitting each branch to single lanes and then doing
even/odd merging would be the brute-force fallback). Not sure
how much we can or should rely on the SLP optimize pass to handle
this.
* tree-vect-slp.cc (vect_build_slp_instance): Do not split
store dataref groups on loop SLP discovery failure but create
a single SLP instance for the stores but branch to SLP sub-trees
and merge with a series of VEC_PERM nodes.
---
gcc/tree-vect-slp.cc | 240 ++++++++++++++++++++++++++++++++++++++-----
1 file changed, 214 insertions(+), 26 deletions(-)
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 43f2c153bf0..873748b0a72 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -3468,12 +3468,7 @@ vect_build_slp_instance (vec_info *vinfo,
return true;
}
}
- else
- {
- /* Failed to SLP. */
- /* Free the allocated memory. */
- scalar_stmts.release ();
- }
+ /* Failed to SLP. */
stmt_vec_info stmt_info = stmt_info_;
/* Try to break the group up into pieces. */
@@ -3491,6 +3486,9 @@ vect_build_slp_instance (vec_info *vinfo,
if (is_a <bb_vec_info> (vinfo)
&& (i > 1 && i < group_size))
{
+ /* Free the allocated memory. */
+ scalar_stmts.release ();
+
tree scalar_type
= TREE_TYPE (DR_REF (STMT_VINFO_DATA_REF (stmt_info)));
tree vectype = get_vectype_for_scalar_type (vinfo, scalar_type,
@@ -3535,38 +3533,228 @@ vect_build_slp_instance (vec_info *vinfo,
}
}
- /* For loop vectorization split into arbitrary pieces of size > 1. */
- if (is_a <loop_vec_info> (vinfo)
- && (i > 1 && i < group_size)
- && !vect_slp_prefer_store_lanes_p (vinfo, stmt_info, group_size, i))
+ /* For loop vectorization split the RHS into arbitrary pieces of
+ size >= 1. */
+ else if (is_a <loop_vec_info> (vinfo)
+ && (i > 0 && i < group_size)
+ && !vect_slp_prefer_store_lanes_p (vinfo,
+ stmt_info, group_size, i))
{
- unsigned group1_size = i;
-
if (dump_enabled_p ())
dump_printf_loc (MSG_NOTE, vect_location,
"Splitting SLP group at stmt %u\n", i);
- stmt_vec_info rest = vect_split_slp_store_group (stmt_info,
- group1_size);
- /* Loop vectorization cannot handle gaps in stores, make sure
- the split group appears as strided. */
- STMT_VINFO_STRIDED_P (rest) = 1;
- DR_GROUP_GAP (rest) = 0;
- STMT_VINFO_STRIDED_P (stmt_info) = 1;
- DR_GROUP_GAP (stmt_info) = 0;
+ /* Analyze the stored values and pinch them together with
+ a permute node so we can preserve the whole store group. */
+ auto_vec<slp_tree> rhs_nodes;
+
+ /* Calculate the unrolling factor based on the smallest type. */
+ poly_uint64 unrolling_factor = 1;
+
+ unsigned int start = 0, end = i;
+ while (start < group_size)
+ {
+ gcc_assert (end - start >= 1);
+ vec<stmt_vec_info> substmts;
+ substmts.create (end - start);
+ for (unsigned j = start; j < end; ++j)
+ substmts.quick_push (scalar_stmts[j]);
+ max_nunits = 1;
+ node = vect_build_slp_tree (vinfo, substmts, end - start,
+ &max_nunits,
+ matches, limit, &tree_size, bst_map);
+ if (node)
+ {
+ /* ??? Possibly not safe, but not sure how to check
+ and fail SLP build? */
+ unrolling_factor
+ = force_common_multiple (unrolling_factor,
+ calculate_unrolling_factor
+ (max_nunits, end - start));
+ rhs_nodes.safe_push (node);
+ start = end;
+ end = group_size;
+ }
+ else
+ {
+ substmts.release ();
+ if (end - start == 1)
+ {
+ /* Single-lane discovery failed. Free ressources. */
+ for (auto node : rhs_nodes)
+ vect_free_slp_tree (node);
+ scalar_stmts.release ();
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "SLP discovery failed\n");
+ return false;
+ }
+
+ /* ??? It really happens that we soft-fail SLP
+ build at a mismatch but the matching part hard-fails
+ later. As we know we arrived here with a group
+ larger than one try a group of size one! */
+ if (!matches[0])
+ end = start + 1;
+ else
+ for (unsigned j = start; j < end; j++)
+ if (!matches[j - start])
+ {
+ end = j;
+ break;
+ }
+ }
+ }
+
+ /* Now we assume we can build the root SLP node from all
+ stores. */
+ node = vect_create_new_slp_node (scalar_stmts, 1);
+ SLP_TREE_VECTYPE (node) = SLP_TREE_VECTYPE (rhs_nodes[0]);
+ /* And a permute merging all RHS SLP trees. */
+ slp_tree perm = vect_create_new_slp_node (rhs_nodes.length (),
+ VEC_PERM_EXPR);
+ SLP_TREE_CHILDREN (node).quick_push (perm);
+ SLP_TREE_LANE_PERMUTATION (perm).create (group_size);
+ SLP_TREE_VECTYPE (perm) = SLP_TREE_VECTYPE (node);
+ SLP_TREE_LANES (perm) = group_size;
+ /* ??? We should set this NULL but that's not expected. */
+ SLP_TREE_REPRESENTATIVE (perm)
+ = SLP_TREE_REPRESENTATIVE (SLP_TREE_CHILDREN (rhs_nodes[0])[0]);
+ for (unsigned j = 0; j < rhs_nodes.length (); ++j)
+ {
+ SLP_TREE_CHILDREN (perm)
+ .quick_push (SLP_TREE_CHILDREN (rhs_nodes[j])[0]);
+ for (unsigned k = 0;
+ k < SLP_TREE_SCALAR_STMTS (rhs_nodes[j]).length (); ++k)
+ {
+ /* ??? We should populate SLP_TREE_SCALAR_STMTS
+ or SLP_TREE_SCALAR_OPS but then we might have
+ a mix of both in our children. */
+ SLP_TREE_LANE_PERMUTATION (perm)
+ .quick_push (std::make_pair (j, k));
+ }
+ }
+
+ /* Now we have a single permute node but we cannot code-generate
+ the case with more than two inputs.
+ Perform pairwise reduction, reducing the two inputs
+ with the least number of lanes to one and then repeat until
+ we end up with two inputs. That scheme makes sure we end
+ up with permutes satisfying the restriction of requiring
+ at most two vector inputs to produce a single vector output. */
+ while (SLP_TREE_CHILDREN (perm).length () > 2)
+ {
+ /* Pick the two nodes with the least number of lanes,
+ prefer the earliest candidate and maintain ai < bi. */
+ int ai = -1;
+ int bi = -1;
+ for (unsigned ci = 0;
+ ci < SLP_TREE_CHILDREN (perm).length (); ++ci)
+ {
+ if (ai == -1)
+ ai = ci;
+ else if (bi == -1)
+ bi = ci;
+ else if ((SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[ci])
+ < SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[ai]))
+ || (SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[ci])
+ < SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[bi])))
+ {
+ if (SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[ai])
+ <= SLP_TREE_LANES (SLP_TREE_CHILDREN (perm)[bi]))
+ bi = ci;
+ else
+ {
+ ai = bi;
+ bi = ci;
+ }
+ }
+ }
+
+ /* Produce a merge of nodes ai and bi. */
+ slp_tree a = SLP_TREE_CHILDREN (perm)[ai];
+ slp_tree b = SLP_TREE_CHILDREN (perm)[bi];
+ unsigned n = SLP_TREE_LANES (a) + SLP_TREE_LANES (b);
+ slp_tree permab = vect_create_new_slp_node (2, VEC_PERM_EXPR);
+ SLP_TREE_LANES (permab) = n;
+ SLP_TREE_LANE_PERMUTATION (permab).create (n);
+ SLP_TREE_VECTYPE (permab) = SLP_TREE_VECTYPE (perm); /* ??? */
+ /* ??? We should set this NULL but that's not expected. */
+ SLP_TREE_REPRESENTATIVE (permab) = SLP_TREE_REPRESENTATIVE (perm);
+ SLP_TREE_CHILDREN (permab).quick_push (a);
+ for (unsigned k = 0; k < SLP_TREE_LANES (a); ++k)
+ SLP_TREE_LANE_PERMUTATION (permab)
+ .quick_push (std::make_pair (0, k));
+ SLP_TREE_CHILDREN (permab).quick_push (b);
+ for (unsigned k = 0; k < SLP_TREE_LANES (b); ++k)
+ SLP_TREE_LANE_PERMUTATION (permab)
+ .quick_push (std::make_pair (1, k));
+
+ /* Put the merged node into 'perm', in place of a */
+ SLP_TREE_CHILDREN (perm)[ai] = permab;
+ /* Adjust the references to b in the permutation
+ of perm and to the later children which we'll
+ remove. */
+ for (unsigned k = 0; k < SLP_TREE_LANES (perm); ++k)
+ {
+ std::pair<unsigned, unsigned> &p
+ = SLP_TREE_LANE_PERMUTATION (perm)[k];
+ if (p.first == (unsigned) bi)
+ {
+ p.first = ai;
+ p.second += SLP_TREE_LANES (a);
+ }
+ else if (p.first > (unsigned) bi)
+ p.first--;
+ }
+ SLP_TREE_CHILDREN (perm).ordered_remove (bi);
+ }
+
+ /* Create a new SLP instance. */
+ slp_instance new_instance = XNEW (class _slp_instance);
+ SLP_INSTANCE_TREE (new_instance) = node;
+ SLP_INSTANCE_UNROLLING_FACTOR (new_instance) = unrolling_factor;
+ SLP_INSTANCE_LOADS (new_instance) = vNULL;
+ SLP_INSTANCE_ROOT_STMTS (new_instance) = root_stmt_infos;
+ SLP_INSTANCE_REMAIN_DEFS (new_instance) = remain;
+ SLP_INSTANCE_KIND (new_instance) = kind;
+ new_instance->reduc_phis = NULL;
+ new_instance->cost_vec = vNULL;
+ new_instance->subgraph_entries = vNULL;
+
+ if (dump_enabled_p ())
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "SLP size %u vs. limit %u.\n",
+ tree_size, max_tree_size);
- bool res = vect_analyze_slp_instance (vinfo, bst_map, stmt_info,
- kind, max_tree_size, limit);
- if (i + 1 < group_size)
- res |= vect_analyze_slp_instance (vinfo, bst_map,
- rest, kind, max_tree_size, limit);
+ vinfo->slp_instances.safe_push (new_instance);
+
+ /* ??? We've replaced the old SLP_INSTANCE_GROUP_SIZE with
+ the number of scalar stmts in the root in a few places.
+ Verify that assumption holds. */
+ gcc_assert (SLP_TREE_SCALAR_STMTS (SLP_INSTANCE_TREE (new_instance))
+ .length () == group_size);
- return res;
+ if (dump_enabled_p ())
+ {
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "Final SLP tree for instance %p:\n",
+ (void *) new_instance);
+ vect_print_slp_graph (MSG_NOTE, vect_location,
+ SLP_INSTANCE_TREE (new_instance));
+ }
+ return true;
}
+ else
+ /* Free the allocated memory. */
+ scalar_stmts.release ();
/* Even though the first vector did not all match, we might be able to
SLP
(some) of the remainder. FORNOW ignore this possibility. */
}
+ else
+ /* Free the allocated memory. */
+ scalar_stmts.release ();
/* Failed to SLP. */
if (dump_enabled_p ())
--
2.35.3
