From: Richard Biener <rguenther@suse.de>
Date: Fri, 30 May 2025 06:54:10 +0000 (+0200)
Subject: tree-optimization/120457 - avoid lowering of some single-element interleave
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0291f53f8d2343ca0d39589ebffc31d9c328d6ab;p=thirdparty%2Fgcc.git

tree-optimization/120457 - avoid lowering of some single-element interleave

The following makes sure we are not lowering single-element interleaving
schemes in a way that defeats load vectorizing later but allows the
VMAT_ELEMENTWISE fallback to be used.

	PR tree-optimization/120457
	* tree-vect-slp.cc (vect_lower_load_permutations): Implement
	the same heuristics as load vectorization for single-element
	interleaving that spans multiple vectors.
---

diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
index fb2262a6137..dc89da3bf17 100644
--- a/gcc/tree-vect-slp.cc
+++ b/gcc/tree-vect-slp.cc
@@ -4557,6 +4557,15 @@ vect_lower_load_permutations (loop_vec_info loop_vinfo,
       if (!SLP_TREE_CHILDREN (load).is_empty ())
 	continue;
 
+      /* For single-element interleaving spanning multiple vectors avoid
+	 lowering, we want to use VMAT_ELEMENTWISE later.  */
+      if (ld_lanes_lanes == 0
+	  && SLP_TREE_LANES (load) == 1
+	  && !DR_GROUP_NEXT_ELEMENT (first)
+	  && maybe_gt (group_lanes,
+		       TYPE_VECTOR_SUBPARTS (SLP_TREE_VECTYPE (load))))
+	return;
+
       /* We want to pattern-match special cases here and keep those
 	 alone.  Candidates are splats and load-lane.  */