tree-optimization/97733 - fix SLP of reductions with zero relevant

This adds a missing check.

2020-11-06  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97733
	* tree-vect-slp.c (vect_analyze_slp_instance): If less
	than two reductions were relevant or live do nothing.

diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 9c63983..4d1f17b 100644 (file)
--- a/gcc/tree-vect-slp.c
+++ b/gcc/tree-vect-slp.c
@@ -2539,6 +2539,9 @@ vect_analyze_slp_instance (vec_info *vinfo,
        if (STMT_VINFO_RELEVANT_P (next_info)
            || STMT_VINFO_LIVE_P (next_info))
          scalar_stmts.quick_push (next_info);
+      /* If less than two were relevant/live there's nothing to SLP.  */
+      if (scalar_stmts.length () < 2)
+       return false;
     }
 
   /* Build the tree for the SLP instance.  */