The following emulates classical interleaving for SLP load permutes
that we are unlikely handling natively. This is to handle cases
where interleaving (or load/store-lanes) is the optimal choice for
vectorizing even when we are doing that within SLP. An example
would be
void foo (int * __restrict a, int * b)
{
for (int i = 0; i < 16; ++i)
{
a[4*i + 0] = b[4*i + 0] * 3;
a[4*i + 1] = b[4*i + 1] + 3;
a[4*i + 2] = (b[4*i + 2] * 3 + 3);
a[4*i + 3] = b[4*i + 3] * 3;
}
}
where currently the SLP store is merging four single-lane SLP
sub-graphs but none of the loads in it can be code-generated
with V4SImode vectors and a VF of four as the permutes would need
three vectors.
The patch introduces a lowering phase after SLP discovery but
before SLP pattern recognition or permute optimization that
analyzes all loads from the same dataref group and creates an
interleaving scheme starting from an unpermuted load.
What can be handled is quite restrictive, matching only a subset
of the non-SLP interleaving cases (the power-of-two group size
ones, in addition only cases without gaps). The interleaving
vectorization in addition can handle size 3 and 5 - but I am not
sure if it's possible to do that in a VL agnostic way. It
should be still possible to set up the SLP graph in a way that
a load-lane could be matched from SLP pattern recognition.
As said gaps are currently not handled - for SLP we have a
representational issue that SLP_TREE_SCALAR_STMTS for "gap lanes"
would need to be filled in some way (even if we just push NULL).
The patch misses multi-level even/odd handling as well as CSEing
intermediate generated permutes. Both is quite straight-forward
to add, but eventually there's a better or more general strategy
for lowering? The main goal of the patch is to avoid falling
back to non-SLP for cases the interleaving code handles.
Comments and suggestions welcome, esp. what representation
you'd think is suitable for SLP pattern matching to
load/store-lane and how to represent that? Maybe this lowering
should happen directly in vect_lower_load_permutations?
Thanks,
Richard.
* tree-vect-slp.cc (vllp_cmp): New function.
(vect_lower_load_permutations): Likewise.
(vect_analyze_slp): Call it.
---
gcc/tree-vect-slp.cc | 279 +++++++++++++++++++++++++++++++++++++++++++
1 file changed, 279 insertions(+)
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 7e3d0107b4e..766b773452f 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -3839,6 +3839,279 @@ vect_analyze_slp_instance (vec_info *vinfo,
return res;
}
+/* qsort comparator ordering SLP load nodes. */
+
+static int
+vllp_cmp (const void *a_, const void *b_)
+{
+ const slp_tree a = *(const slp_tree *)a_;
+ const slp_tree b = *(const slp_tree *)b_;
+ stmt_vec_info a0 = SLP_TREE_SCALAR_STMTS (a)[0];
+ stmt_vec_info b0 = SLP_TREE_SCALAR_STMTS (b)[0];
+ if (STMT_VINFO_GROUPED_ACCESS (a0)
+ && STMT_VINFO_GROUPED_ACCESS (b0)
+ && DR_GROUP_FIRST_ELEMENT (a0) == DR_GROUP_FIRST_ELEMENT (b0))
+ {
+ /* Same group, order after lanes used. */
+ if (SLP_TREE_LANES (a) < SLP_TREE_LANES (b))
+ return 1;
+ else if (SLP_TREE_LANES (a) > SLP_TREE_LANES (b))
+ return -1;
+ else
+ {
+ /* Try to order loads using the same lanes together, breaking
+ the tie with the lane number that first differs. */
+ if (!SLP_TREE_LOAD_PERMUTATION (a).exists ()
+ && !SLP_TREE_LOAD_PERMUTATION (b).exists ())
+ return 0;
+ else if (SLP_TREE_LOAD_PERMUTATION (a).exists ()
+ && !SLP_TREE_LOAD_PERMUTATION (b).exists ())
+ return 1;
+ else if (!SLP_TREE_LOAD_PERMUTATION (a).exists ()
+ && SLP_TREE_LOAD_PERMUTATION (b).exists ())
+ return -1;
+ else
+ {
+ for (unsigned i = 0; i < SLP_TREE_LANES (a); ++i)
+ if (SLP_TREE_LOAD_PERMUTATION (a)[i]
+ != SLP_TREE_LOAD_PERMUTATION (b)[i])
+ {
+ /* In-order lane first, that's what the above case for
+ no permutation does. */
+ if (SLP_TREE_LOAD_PERMUTATION (a)[i] == i)
+ return -1;
+ else if (SLP_TREE_LOAD_PERMUTATION (b)[i] == i)
+ return 1;
+ else if (SLP_TREE_LOAD_PERMUTATION (a)[i]
+ < SLP_TREE_LOAD_PERMUTATION (b)[i])
+ return -1;
+ else
+ return 1;
+ }
+ return 0;
+ }
+ }
+ }
+ else /* Different groups or non-groups. */
+ {
+ /* Order groups as their first element to keep them together. */
+ if (STMT_VINFO_GROUPED_ACCESS (a0))
+ a0 = DR_GROUP_FIRST_ELEMENT (a0);
+ if (STMT_VINFO_GROUPED_ACCESS (b0))
+ b0 = DR_GROUP_FIRST_ELEMENT (b0);
+ if (a0 == b0)
+ return 0;
+ /* Tie using UID. */
+ else if (gimple_uid (STMT_VINFO_STMT (a0))
+ < gimple_uid (STMT_VINFO_STMT (b0)))
+ return -1;
+ else
+ {
+ gcc_assert (gimple_uid (STMT_VINFO_STMT (a0))
+ != gimple_uid (STMT_VINFO_STMT (b0)));
+ return 1;
+ }
+ }
+}
+
+/* Process the set of LOADS that are all from the same dataref group. */
+
+static void
+vect_lower_load_permutations (loop_vec_info loop_vinfo,
+ scalar_stmts_to_slp_tree_map_t *bst_map,
+ const array_slice<slp_tree> &loads)
+{
+ /* We at this point want to lower without a fixed VF or vector
+ size in mind which means we cannot actually compute whether we
+ need three or more vectors for a load permutation yet. So always
+ lower. */
+ stmt_vec_info first
+ = DR_GROUP_FIRST_ELEMENT (SLP_TREE_SCALAR_STMTS (loads[0])[0]);
+
+ /* ??? In principle we have to consider a gap up to the next full
+ vector, but we have to actually represent a scalar stmt for the
+ gaps value so delay handling this. The same is true for
+ inbetween gaps which the load places in the load-permutation
+ represent. It's probably not worth trying an intermediate packing
+ to vectors without gap even if that might handle some more cases.
+ Instead get the gap case correct in some way. */
+ unsigned group_lanes = 0;
+ for (stmt_vec_info s = first; s; s = DR_GROUP_NEXT_ELEMENT (s))
+ {
+ if ((s == first && DR_GROUP_GAP (s) != 0)
+ || (s != first && DR_GROUP_GAP (s) != 1))
+ return;
+ group_lanes++;
+ }
+ /* Only a power-of-two number of lanes matches interleaving. */
+ if (exact_log2 (group_lanes) == -1)
+ return;
+
+ for (slp_tree load : loads)
+ {
+ /* Leave masked or gather loads alone for now. */
+ if (!SLP_TREE_CHILDREN (load).is_empty ())
+ continue;
+
+ /* We need to lower only loads of less than half of the groups
+ lanes, including duplicate lanes. */
+ if (SLP_TREE_LANES (load) >= group_lanes / 2)
+ continue;
+
+ /* Lower by reducing the group to half its size using an
+ interleaving scheme. For this try to compute whether all
+ elements needed for this loads are in even or odd elements of
+ a even/odd decomposition with N consecutive elements.
+ Thus { e, e, o, o, e, e, o, o } woud be an even/odd decomposition
+ with N == 2. */
+ unsigned even = (1 << ceil_log2 (DR_GROUP_SIZE (first))) - 1;
+ unsigned odd = even;
+ for (unsigned l : SLP_TREE_LOAD_PERMUTATION (load))
+ {
+ even &= ~l;
+ odd &= l;
+ }
+ /* Give up when this doesn't match up with an interleaving scheme. */
+ if (!even && !odd)
+ continue;
+
+ /* First build (and possibly re-use) a load node for the
+ unpermuted group. */
+ vec<stmt_vec_info> stmts;
+ stmts.create (group_lanes);
+ for (stmt_vec_info s = first; s; s = DR_GROUP_NEXT_ELEMENT (s))
+ stmts.quick_push (s);
+ poly_uint64 max_nunits;
+ bool *matches = XALLOCAVEC (bool, group_lanes);
+ unsigned limit = 1;
+ unsigned tree_size = 0;
+ slp_tree l0 = vect_build_slp_tree (loop_vinfo, stmts,
+ group_lanes,
+ &max_nunits, matches, &limit,
+ &tree_size, bst_map);
+
+ /* Build the permute to get the original load permutation order. */
+ lane_permutation_t final_perm;
+ final_perm.create (SLP_TREE_LANES (load));
+ for (unsigned i = 0; i < SLP_TREE_LANES (load); ++i)
+ final_perm.quick_push
+ (std::make_pair (0, SLP_TREE_LOAD_PERMUTATION (load)[i]));
+
+ /* Now build a even or odd extraction from the unpermuted load. */
+ lane_permutation_t perm;
+ perm.create (group_lanes / 2);
+ unsigned level;
+ if (even
+ && ((level = 1 << ctz_hwi (even)), true)
+ && group_lanes % (2 * level) == 0)
+ {
+ /* { 0, 1, ... 4, 5 ..., } */
+ unsigned level = 1 << ctz_hwi (even);
+ for (unsigned i = 0; i < group_lanes / 2 / level; ++i)
+ for (unsigned j = 0; j < level; ++j)
+ perm.quick_push (std::make_pair (0, 2 * i * level + j));
+ }
+ else if (odd)
+ {
+ /* { ..., 2, 3, ... 6, 7 } */
+ unsigned level = 1 << ctz_hwi (odd);
+ gcc_assert (group_lanes % (2 * level) == 0);
+ for (unsigned i = 0; i < group_lanes / 2 / level; ++i)
+ for (unsigned j = 0; j < level; ++j)
+ perm.quick_push (std::make_pair (0, (2 * i + 1) * level + j));
+ }
+ else
+ gcc_unreachable ();
+
+ /* And update final_perm. */
+ for (unsigned i = 0; i < SLP_TREE_LANES (load); ++i)
+ {
+ unsigned l = final_perm[i].second;
+ unsigned j;
+ for (j = 0; j < perm.length (); ++j)
+ if (perm[j].second == l)
+ {
+ final_perm[i].second = j;
+ break;
+ }
+ gcc_assert (j < perm.length ());
+ }
+
+ slp_tree p = vect_create_new_slp_node (1, VEC_PERM_EXPR);
+ SLP_TREE_CHILDREN (p).quick_push (l0);
+ SLP_TREE_LANE_PERMUTATION (p) = perm;
+ SLP_TREE_VECTYPE (p) = SLP_TREE_VECTYPE (load);
+ SLP_TREE_LANES (p) = perm.length ();
+ SLP_TREE_REPRESENTATIVE (p) = SLP_TREE_REPRESENTATIVE (load);
+ /* ??? We should have scalar stmts for this and use bst_map
+ to CSE. But we do not want to pick up original SLP load
+ nodes with a load-permutation here. */
+ /* ??? We need to iterate if group_lanes / 2 is still too large. */
+ /* ??? Ideally pick the best even/odd scheme usable for
+ most of the loads. -> do a multi-step scheme? */
+
+ /* And finally from the ordered reduction node create the
+ permute to shuffle the lanes into the original load-permutation
+ order. We replace the original load node with this. */
+ SLP_TREE_CODE (load) = VEC_PERM_EXPR;
+ SLP_TREE_LOAD_PERMUTATION (load).release ();
+ SLP_TREE_LANE_PERMUTATION (load) = final_perm;
+ SLP_TREE_CHILDREN (load).create (1);
+ SLP_TREE_CHILDREN (load).quick_push (p);
+ }
+}
+
+/* Transform SLP loads in the SLP graph created by SLP discovery to
+ group loads from the same group and lower load permutations that
+ are unlikely to be supported into a series of permutes.
+ In the degenerate case of having only single-lane SLP instances
+ this should result in a series of permute nodes emulating an
+ interleaving scheme. */
+
+static void
+vect_lower_load_permutations (loop_vec_info loop_vinfo,
+ scalar_stmts_to_slp_tree_map_t *bst_map)
+{
+ /* Gather and sort loads across all instances. */
+ hash_set<slp_tree> visited;
+ auto_vec<slp_tree> loads;
+ for (auto inst : loop_vinfo->slp_instances)
+ vect_gather_slp_loads (loads, SLP_INSTANCE_TREE (inst), visited);
+ if (loads.is_empty ())
+ return;
+ loads.qsort (vllp_cmp);
+
+ /* Now process each dataref group separately. */
+ unsigned firsti = 0;
+ for (unsigned i = 1; i < loads.length (); ++i)
+ {
+ slp_tree first = loads[firsti];
+ slp_tree next = loads[i];
+ stmt_vec_info a0 = SLP_TREE_SCALAR_STMTS (first)[0];
+ stmt_vec_info b0 = SLP_TREE_SCALAR_STMTS (next)[0];
+ if (STMT_VINFO_GROUPED_ACCESS (a0)
+ && STMT_VINFO_GROUPED_ACCESS (b0)
+ && DR_GROUP_FIRST_ELEMENT (a0) == DR_GROUP_FIRST_ELEMENT (b0))
+ continue;
+ /* Just one SLP load of a possible group, leave those alone. */
+ if (i == firsti + 1)
+ {
+ firsti = i;
+ continue;
+ }
+ /* Now we have multiple SLP loads of the same group from
+ firsti to i - 1. */
+ vect_lower_load_permutations (loop_vinfo, bst_map,
+ make_array_slice (&loads[firsti],
+ i - firsti));
+ firsti = i;
+ }
+ if (firsti < loads.length () - 1)
+ vect_lower_load_permutations (loop_vinfo, bst_map,
+ make_array_slice (&loads[firsti],
+ loads.length () - firsti));
+}
+
/* Check if there are stmts in the loop can be vectorized using SLP. Build SLP
trees of packed scalar stmts if SLP is possible. */
@@ -3982,6 +4255,12 @@ vect_analyze_slp (vec_info *vinfo, unsigned
max_tree_size)
}
}
+ /* When we end up with load permutations that we cannot possibly handle,
+ like those requiring three vector inputs, lower them using interleaving
+ like schemes. */
+ if (loop_vec_info loop_vinfo = dyn_cast <loop_vec_info> (vinfo))
+ vect_lower_load_permutations (loop_vinfo, bst_map);
+
hash_set<slp_tree> visited_patterns;
slp_tree_to_load_perm_map_t perm_cache;
slp_compat_nodes_map_t compat_cache;
--
2.35.3
