diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
index 99021a82df4..6912de9b43c 100644
--- a/gcc/fold-const.cc
+++ b/gcc/fold-const.cc
@@ -10541,15 +10541,33 @@ fold_vec_perm (tree type, tree arg0, tree arg1, const vec_perm_indices &sel)
   unsigned HOST_WIDE_INT nelts;
   bool need_ctor = false;
 
-  if (!sel.length ().is_constant (&nelts))
-    return NULL_TREE;
-  gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type), nelts)
-	      && known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)), nelts)
-	      && known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg1)), nelts));
+  gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (type),
+			sel.length ()));
+  gcc_assert (known_eq (TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)),
+			TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg1))));
+
   if (TREE_TYPE (TREE_TYPE (arg0)) != TREE_TYPE (type)
       || TREE_TYPE (TREE_TYPE (arg1)) != TREE_TYPE (type))
     return NULL_TREE;
 
+  /* If result vector has greater length than input vector,
+     then allow permuting two vectors as long as:
+     a) sel.nelts_per_pattern == 1
+     b) sel.npatterns == len of input vector.
+     The intent is to permute input vectors, and
+     dup the elements in resulting vector to target vector length.  */
+
+  if (maybe_gt (TYPE_VECTOR_SUBPARTS (type),
+		TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0))))
+    {
+      nelts = sel.encoding ().npatterns ();
+      if (sel.encoding ().nelts_per_pattern () != 1
+	  || (!known_eq (nelts, TYPE_VECTOR_SUBPARTS (TREE_TYPE (arg0)))))
+	return NULL_TREE;
+    }
+  else if (!sel.length ().is_constant (&nelts))
+    return NULL_TREE;
+
   tree *in_elts = XALLOCAVEC (tree, nelts * 2);
   if (!vec_cst_ctor_to_array (arg0, nelts, in_elts)
       || !vec_cst_ctor_to_array (arg1, nelts, in_elts + nelts))
diff --git a/gcc/tree-pretty-print.cc b/gcc/tree-pretty-print.cc
index 47371d8bcbe..7e706857f43 100644
--- a/gcc/tree-pretty-print.cc
+++ b/gcc/tree-pretty-print.cc
@@ -2602,6 +2602,9 @@ dump_generic_node (pretty_printer *pp, tree node, int spc, dump_flags_t flags,
 		pp_space (pp);
 	      }
 	  }
+	if (VECTOR_TYPE_P (TREE_TYPE (node))
+	    && !TYPE_VECTOR_SUBPARTS (TREE_TYPE (node)).is_constant ())
+	  pp_string (pp, ", ... ");
 	pp_right_brace (pp);
       }
       break;