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

[Richard Biener]

This adds a missing check.

Bootstrap & regtest running on x86_64-unknown-linux-gnu.

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.
---
 gcc/tree-vect-slp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/gcc/tree-vect-slp.c b/gcc/tree-vect-slp.c
index 9c63983b625..4d1f17bd3fa 100644
--- 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.  */
-- 
2.26.2