Re: [PATCH 2/2] avoid SLP_TREE_REPRESENTATIVE for permutes

On Tue, 18 Aug 2026, Richard Biener wrote:

> The following consistently keeps SLP_TREE_REPRESENTATIVE cleared
> for VEC_PERM_EXPR SLP nodes and verifies this.
> 
> Bootstrapped and tested on x86_64-unknown-linux-gnu, now also
> testing on aarch64-linux-gnu.

aarch64-linux-gnu testing showed I missed two spots in SLP pattern
detection.

The following is what I pushed.

From 233480c124149585b60631b2323a49d409d3f344 Mon Sep 17 00:00:00 2001
From: Richard Biener <[email protected]>
Date: Tue, 18 Aug 2026 13:19:30 +0200
Subject: [PATCH] avoid SLP_TREE_REPRESENTATIVE for permutes
To: [email protected]

The following consistently keeps SLP_TREE_REPRESENTATIVE cleared
for VEC_PERM_EXPR SLP nodes and verifies this.

	* tree-vect-slp.cc (vect_slp_build_two_operator_nodes):
	Set SLP_TREE_REPRESENTATIVE to NULL for the permute nodes.
	(vect_build_slp_tree_2): Likewise.
	(vect_build_slp_store_interleaving): Likewise.
	(vect_lower_load_permutations): Likewise.
	(vect_optimize_slp_pass::get_result_with_layout): Likewise.
	(vect_cse_slp_node_parts): Deal with NULL SLP_TREE_REPRESENTATIVE
	for VEC_PERM nodes.
	(vect_slp_analyze_node_operations_1): Assert permute nodes
	do not have SLP_TREE_REPRESENTATIVE set.
	* tree-vect-slp-patterns.cc (complex_pattern::build): Adjust.
	(vect_build_swap_evenodd_node): Do not set SLP_TREE_REPRESENTATIVE.
	(vect_build_combine_node): Likewise.
---
 gcc/tree-vect-slp-patterns.cc |  7 +------
 gcc/tree-vect-slp.cc          | 18 ++++++++++--------
 2 files changed, 11 insertions(+), 14 deletions(-)

diff --git a/gcc/tree-vect-slp-patterns.cc b/gcc/tree-vect-slp-patterns.cc
index 8a03a25475d..2ff7ce2699f 100644
--- a/gcc/tree-vect-slp-patterns.cc
+++ b/gcc/tree-vect-slp-patterns.cc
@@ -277,7 +277,6 @@ vect_build_swap_evenodd_node (slp_tree node)
   SLP_TREE_CHILDREN (vnode).quick_push (node);
   SLP_TREE_REF_COUNT (vnode) = 1;
   SLP_TREE_LANES (vnode) = SLP_TREE_LANES (node);
-  SLP_TREE_REPRESENTATIVE (vnode) = SLP_TREE_REPRESENTATIVE (node);
   SLP_TREE_REF_COUNT (node)++;
   return vnode;
 }
@@ -535,7 +534,7 @@ complex_pattern::build (vec_info *vinfo)
   FOR_EACH_VEC_ELT (this->m_workset, ix, node)
     {
       /* Calculate the location of the statement in NODE to replace.  */
-      stmt_info = SLP_TREE_REPRESENTATIVE (node);
+      stmt_info = SLP_TREE_SCALAR_STMTS (node)[0];
       gimple* old_stmt = STMT_VINFO_STMT (stmt_info);
       tree lhs_old_stmt = gimple_get_lhs (old_stmt);
       tree type = TREE_TYPE (lhs_old_stmt);
@@ -1006,10 +1005,6 @@ vect_build_combine_node (slp_tree even, slp_tree odd, slp_tree rep)
 
   SLP_TREE_LANES (vnode) = SLP_TREE_LANES (rep);
   gcc_assert (perm.length () == SLP_TREE_LANES (vnode));
-  /* Representation is set to that of the current node as the vectorizer
-     can't deal with VEC_PERMs with no representation, as would be the
-     case with invariants.  */
-  SLP_TREE_REPRESENTATIVE (vnode) = SLP_TREE_REPRESENTATIVE (rep);
   SLP_TREE_VECTYPE (vnode) = SLP_TREE_VECTYPE (rep);
   return vnode;
 }
diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index b2f14e6528a..5b602bcfc71 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -2095,8 +2095,7 @@ vect_slp_build_two_operator_nodes (slp_tree perm, tree vectype,
   SLP_TREE_CODE (perm) = VEC_PERM_EXPR;
   SLP_TREE_VECTYPE (perm) = vectype;
   SLP_TREE_LANES (perm) = group_size;
-  /* ???  We should set this NULL but that's not expected.  */
-  SLP_TREE_REPRESENTATIVE (perm) = oper1;
+  SLP_TREE_REPRESENTATIVE (perm) = NULL;
   SLP_TREE_LANE_PERMUTATION (perm) = lperm;
   SLP_TREE_CHILDREN (perm).quick_push (child1);
   SLP_TREE_CHILDREN (perm).quick_push (child2);
@@ -2309,6 +2308,7 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
 		      SLP_TREE_CODE (node) = VEC_PERM_EXPR;
 		      SLP_TREE_CHILDREN (node).safe_push (unperm_load);
 		      SLP_TREE_LANE_PERMUTATION (node) = lperm;
+		      SLP_TREE_REPRESENTATIVE (node) = NULL;
 		      load_permutation.release ();
 		      return node;
 		    }
@@ -2386,6 +2386,7 @@ vect_build_slp_tree_2 (vec_info *vinfo, slp_tree node,
       SLP_TREE_LANE_PERMUTATION (node) = lperm;
       SLP_TREE_VECTYPE (node) = vectype;
       SLP_TREE_CHILDREN (node).quick_push (vnode);
+      SLP_TREE_REPRESENTATIVE (node) = NULL;
       return node;
     }
   /* When discovery reaches an associatable operation see whether we can
@@ -3316,6 +3317,7 @@ fail:
 	      SLP_TREE_VECTYPE (pnode) = vectype;
 	      SLP_TREE_CHILDREN (pnode).quick_push (child);
 	      SLP_TREE_CHILDREN (pnode).quick_push (child);
+	      SLP_TREE_REPRESENTATIVE (pnode) = NULL;
 	      lane_permutation_t& perm = SLP_TREE_LANE_PERMUTATION (pnode);
 	      children.safe_push (pnode);
 
@@ -3345,6 +3347,7 @@ fail:
       SLP_TREE_CODE (node) = VEC_PERM_EXPR;
       SLP_TREE_CHILDREN (node).quick_push (one);
       SLP_TREE_CHILDREN (node).quick_push (two);
+      SLP_TREE_REPRESENTATIVE (node) = NULL;
       enum tree_code code0 = ERROR_MARK;
       enum tree_code ocode = ERROR_MARK;
       if (gassign *stmt = dyn_cast <gassign *> (stmts[0]->stmt))
@@ -4108,9 +4111,7 @@ vect_build_slp_store_interleaving (vec<slp_tree> &rhs_nodes,
       SLP_TREE_VECTYPE (perm) = SLP_TREE_VECTYPE (node);
       perm->max_nunits = max_nunits;
       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])[l]);
+      SLP_TREE_REPRESENTATIVE (perm) = NULL;
       for (unsigned j = 0; j < rhs_nodes.length (); ++j)
 	{
 	  SLP_TREE_CHILDREN (perm)
@@ -5918,7 +5919,6 @@ vect_lower_load_permutations (loop_vec_info loop_vinfo,
 	  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);
 	  /* ???  As we have scalar stmts for this intermediate permute we
 	     could CSE it via bst_map but we do not want to pick up
 	     another SLP node with a load permutation.  We instead should
@@ -5937,6 +5937,7 @@ vect_lower_load_permutations (loop_vec_info loop_vinfo,
       SLP_TREE_LANE_PERMUTATION (load) = final_perm;
       SLP_TREE_CHILDREN (load).create (1);
       SLP_TREE_CHILDREN (load).quick_push (l0);
+      SLP_TREE_REPRESENTATIVE (load) = NULL;
     }
 }
 
@@ -8077,7 +8078,6 @@ vect_optimize_slp_pass::get_result_with_layout (slp_tree node,
 	  if (to_layout_i != 0)
 	    vect_slp_permute (m_perms[to_layout_i], stmts, true);
 	}
-      SLP_TREE_REPRESENTATIVE (result) = SLP_TREE_REPRESENTATIVE (node);
       SLP_TREE_LANES (result) = num_lanes;
       SLP_TREE_VECTYPE (result) = SLP_TREE_VECTYPE (node);
       result->vertex = -1;
@@ -8659,7 +8659,8 @@ vect_cse_slp_node_parts (hash_set<slp_tree> &visited,
       && SLP_TREE_SCALAR_STMTS (node)[0]
       /* Avoid touching loads which need care with load permutations
 	 and specialities like load-lane representations.  */
-      && !STMT_VINFO_DATA_REF (SLP_TREE_REPRESENTATIVE (node)))
+      && (SLP_TREE_PERMUTE_P (node)
+	  || !STMT_VINFO_DATA_REF (SLP_TREE_REPRESENTATIVE (node))))
     for (slp_tree cand
 	 : part_starts[gimple_uid (SLP_TREE_SCALAR_STMTS (node)[0]->stmt)])
       /* ???  There is a possible ordering/optimality problem in that
@@ -8960,6 +8961,7 @@ vect_slp_analyze_node_operations_1 (vec_info *vinfo, slp_tree node,
   /* Handle purely internal nodes.  */
   if (SLP_TREE_PERMUTE_P (node))
     {
+      gcc_checking_assert (!SLP_TREE_REPRESENTATIVE (node));
       if (!vectorizable_slp_permutation (vinfo, NULL, node, cost_vec))
 	return false;
 
-- 
2.51.0