[gcc r16-5417] tree-optimization/122722 - better SLP reduction group discovery
Richard Biener
rguenth@gcc.gnu.org
Wed Nov 19 13:00:19 GMT 2025
https://gcc.gnu.org/g:97a7d568f3d72076c3f9da062007e3298da9243f
commit r16-5417-g97a7d568f3d72076c3f9da062007e3298da9243f
Author: Richard Biener <rguenther@suse.de>
Date: Tue Nov 18 15:20:44 2025 +0100
tree-optimization/122722 - better SLP reduction group discovery
The following improves the all-or-nothing discovery of reduction
groups to consider sub-groups by trying toplevel "matches" candidates
for this. For simplicity and to limit compile-time failed sub-group
matches are not decomposed further, only the originally failed part
is tried again to discover more sub-groups. Any remaining fails
get picked up by the current single-reduction handling.
PR tree-optimization/122722
* tree-vect-slp.cc (vect_analyze_slp_reductions): New
function, split out from vect_analyze_slp. Try SLP
sub-groups.
(vect_analyze_slp_reduction_group): New helper.
* gcc.dg/vect/slp-reduc-14.c: New testcase.
Diff:
---
gcc/testsuite/gcc.dg/vect/slp-reduc-14.c | 15 ++
gcc/tree-vect-slp.cc | 244 +++++++++++++++++++++++--------
2 files changed, 201 insertions(+), 58 deletions(-)
diff --git a/gcc/testsuite/gcc.dg/vect/slp-reduc-14.c b/gcc/testsuite/gcc.dg/vect/slp-reduc-14.c
new file mode 100644
index 000000000000..7966d23716ad
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/vect/slp-reduc-14.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-additional-options "--param vect-epilogues-nomask=0" } */
+
+void foo (int * __restrict sums, int *a, int *b, int n)
+{
+ for (int i = 0; i < n; ++i)
+ {
+ sums[0] = sums[0] + a[2*i];
+ sums[1] = sums[1] + a[2*i+1];
+ sums[2] = sums[2] + b[2*i];
+ sums[3] = sums[3] + b[2*i+1];
+ }
+}
+
+/* { dg-final { scan-tree-dump-times "SLP discovery of size 2 reduction group" 2 "vect" } } */
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index 07e22ea7ccfa..0ab15fde469d 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -4723,6 +4723,189 @@ vect_analyze_slp_reduction (loop_vec_info vinfo,
return false;
}
+/* Analyze a single SLP reduction group. If successful add a SLP instance
+ for it and return true, otherwise return false and have *MATCHES
+ populated. */
+
+static bool
+vect_analyze_slp_reduction_group (loop_vec_info loop_vinfo,
+ vec<stmt_vec_info> scalar_stmts,
+ scalar_stmts_to_slp_tree_map_t *bst_map,
+ unsigned max_tree_size, unsigned *limit,
+ bool *matches)
+{
+ /* Try to form a reduction group. */
+ unsigned int group_size = scalar_stmts.length ();
+ if (!matches)
+ matches = XALLOCAVEC (bool, group_size);
+ poly_uint64 max_nunits = 1;
+ unsigned tree_size = 0;
+ slp_tree node = vect_build_slp_tree (loop_vinfo, scalar_stmts,
+ group_size,
+ &max_nunits, matches, limit,
+ &tree_size, bst_map);
+ if (!node)
+ return false;
+
+ /* Create a new SLP instance. */
+ slp_instance new_instance = XNEW (class _slp_instance);
+ SLP_INSTANCE_TREE (new_instance) = node;
+ SLP_INSTANCE_LOADS (new_instance) = vNULL;
+ SLP_INSTANCE_ROOT_STMTS (new_instance) = vNULL;
+ SLP_INSTANCE_REMAIN_DEFS (new_instance) = vNULL;
+ SLP_INSTANCE_KIND (new_instance) = slp_inst_kind_reduc_group;
+ 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);
+
+ loop_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);
+
+ if (dump_enabled_p ())
+ {
+ dump_printf_loc (MSG_NOTE, vect_location,
+ "SLP discovery of size %d reduction group "
+ "succeeded\n", group_size);
+ 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;
+}
+
+/* Analyze reductions in LOOP_VINFO and populate SLP instances
+ accordingly. Returns false if something fails. */
+
+static bool
+vect_analyze_slp_reductions (loop_vec_info loop_vinfo,
+ unsigned max_tree_size, unsigned *limit,
+ scalar_stmts_to_slp_tree_map_t *bst_map,
+ bool force_single_lane)
+{
+ if (loop_vinfo->reductions.is_empty ())
+ return true;
+
+ /* Collect reduction statements we can combine into
+ a SLP reduction. */
+ vec<stmt_vec_info> scalar_stmts;
+ scalar_stmts.create (loop_vinfo->reductions.length ());
+ for (auto next_info : loop_vinfo->reductions)
+ {
+ next_info = vect_stmt_to_vectorize (next_info);
+ if ((STMT_VINFO_RELEVANT_P (next_info)
+ || STMT_VINFO_LIVE_P (next_info))
+ /* ??? Make sure we didn't skip a conversion around a
+ reduction path. In that case we'd have to reverse
+ engineer that conversion stmt following the chain using
+ reduc_idx and from the PHI using reduc_def. */
+ && (STMT_VINFO_DEF_TYPE (next_info) == vect_reduction_def
+ || (STMT_VINFO_DEF_TYPE (next_info)
+ == vect_double_reduction_def)))
+ {
+ /* Do not discover SLP reductions combining lane-reducing
+ ops, that will fail later. */
+ if (!force_single_lane
+ && !lane_reducing_stmt_p (STMT_VINFO_STMT (next_info)))
+ scalar_stmts.quick_push (next_info);
+ /* Do SLP discovery for single-lane reductions. */
+ else if (! vect_analyze_slp_reduction (loop_vinfo, next_info,
+ max_tree_size, limit,
+ bst_map,
+ force_single_lane))
+ {
+ scalar_stmts.release ();
+ return false;
+ }
+ }
+ }
+
+ if (scalar_stmts.length () > 1)
+ {
+ /* Try to form a reduction group. */
+ unsigned int group_size = scalar_stmts.length ();
+ bool *matches = XALLOCAVEC (bool, group_size);
+ if (vect_analyze_slp_reduction_group (loop_vinfo, scalar_stmts, bst_map,
+ max_tree_size, limit, matches))
+ return true;
+
+ /* When analysis as a single SLP reduction group failed try to
+ form sub-groups by collecting matching lanes. Do not recurse
+ that on failure (to limit compile-time costs), but recurse
+ for the initial non-matching parts. Everything not covered
+ by a sub-group gets single-reduction treatment. */
+ vec<stmt_vec_info> cands = vNULL;
+ while (matches[0])
+ {
+ cands.truncate (0);
+ cands.reserve (group_size, true);
+ for (unsigned i = 0; i < group_size; ++i)
+ if (matches[i])
+ cands.quick_push (scalar_stmts[i]);
+
+ /* Try to form a reduction group. */
+ if (vect_analyze_slp_reduction_group (loop_vinfo, cands, bst_map,
+ max_tree_size, limit, NULL))
+ cands = vNULL;
+ else
+ {
+ /* Do SLP discovery for single-lane reductions. */
+ for (auto stmt_info : cands)
+ if (! vect_analyze_slp_reduction (loop_vinfo,
+ vect_stmt_to_vectorize
+ (stmt_info),
+ max_tree_size, limit,
+ bst_map, force_single_lane))
+ {
+ scalar_stmts.release ();
+ cands.release ();
+ return false;
+ }
+ }
+ /* Remove the handled stmts from scalar_stmts and try again,
+ possibly repeating the above with updated matches[]. */
+ unsigned j = 0;
+ for (unsigned i = 0; i < group_size; ++i)
+ if (!matches[i])
+ {
+ scalar_stmts[j] = scalar_stmts[i];
+ ++j;
+ }
+ scalar_stmts.truncate (j);
+ group_size = scalar_stmts.length ();
+ if (vect_analyze_slp_reduction_group (loop_vinfo, scalar_stmts,
+ bst_map, max_tree_size, limit,
+ matches))
+ return true;
+ }
+ }
+ /* Do SLP discovery for single-lane reductions. */
+ for (auto stmt_info : scalar_stmts)
+ if (! vect_analyze_slp_reduction (loop_vinfo,
+ vect_stmt_to_vectorize (stmt_info),
+ max_tree_size, limit,
+ bst_map, force_single_lane))
+ {
+ scalar_stmts.release ();
+ return false;
+ }
+
+ scalar_stmts.release ();
+ return true;
+}
+
/* 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 group. */
@@ -5617,64 +5800,9 @@ vect_analyze_slp (vec_info *vinfo, unsigned max_tree_size,
if (loop_vec_info loop_vinfo = dyn_cast <loop_vec_info> (vinfo))
{
/* Find SLP sequences starting from groups of reductions. */
- if (loop_vinfo->reductions.length () > 0)
- {
- /* Collect reduction statements we can combine into
- a SLP reduction. */
- vec<stmt_vec_info> scalar_stmts;
- scalar_stmts.create (loop_vinfo->reductions.length ());
- for (auto next_info : loop_vinfo->reductions)
- {
- next_info = vect_stmt_to_vectorize (next_info);
- if ((STMT_VINFO_RELEVANT_P (next_info)
- || STMT_VINFO_LIVE_P (next_info))
- /* ??? Make sure we didn't skip a conversion around a
- reduction path. In that case we'd have to reverse
- engineer that conversion stmt following the chain using
- reduc_idx and from the PHI using reduc_def. */
- && (STMT_VINFO_DEF_TYPE (next_info) == vect_reduction_def
- || (STMT_VINFO_DEF_TYPE (next_info)
- == vect_double_reduction_def)))
- {
- /* Do not discover SLP reductions combining lane-reducing
- ops, that will fail later. */
- if (!force_single_lane
- && !lane_reducing_stmt_p (STMT_VINFO_STMT (next_info)))
- scalar_stmts.quick_push (next_info);
- /* Do SLP discovery for single-lane reductions. */
- else if (! vect_analyze_slp_reduction (loop_vinfo, next_info,
- max_tree_size, &limit,
- bst_map,
- force_single_lane))
- return opt_result::failure_at (vect_location,
- "SLP build failed.\n");
- }
- }
- /* Save for re-processing on failure. */
- vec<stmt_vec_info> saved_stmts = scalar_stmts.copy ();
- vec<stmt_vec_info> roots = vNULL;
- vec<tree> remain = vNULL;
- if (scalar_stmts.length () <= 1
- || !vect_build_slp_instance (loop_vinfo,
- slp_inst_kind_reduc_group,
- scalar_stmts, roots, remain,
- max_tree_size, &limit, bst_map,
- force_single_lane))
- {
- if (scalar_stmts.length () <= 1)
- scalar_stmts.release ();
- /* Do SLP discovery for single-lane reductions. */
- for (auto stmt_info : saved_stmts)
- if (! vect_analyze_slp_reduction (loop_vinfo,
- vect_stmt_to_vectorize
- (stmt_info),
- max_tree_size, &limit,
- bst_map, force_single_lane))
- return opt_result::failure_at (vect_location,
- "SLP build failed.\n");
- }
- saved_stmts.release ();
- }
+ if (!vect_analyze_slp_reductions (loop_vinfo, max_tree_size, &limit,
+ bst_map, force_single_lane))
+ return opt_result::failure_at (vect_location, "SLP build failed.\n");
/* Make sure to vectorize only-live stmts, usually inductions. */
for (edge e : get_loop_exit_edges (LOOP_VINFO_LOOP (loop_vinfo)))
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