diff --git a/gcc/testsuite/c-c++-common/Wstringop-overflow.c b/gcc/testsuite/c-c++-common/Wstringop-overflow.c
index 5757a23141e..9829fe14116 100644
--- a/gcc/testsuite/c-c++-common/Wstringop-overflow.c
+++ b/gcc/testsuite/c-c++-common/Wstringop-overflow.c
@@ -90,8 +90,8 @@ void test_strncat (char **d, const char* s, int i)
   }
 
   {
-    size_t n = i < strlen (s) ? i : strlen (s);   /* { dg-message "length computed here" } */
-    T (d, s, n);                  /* { dg-message ".strncat\[^\n\r\]* specified bound depends on the length of the source argument" } */
+    size_t n = i < strlen (s) ? i : strlen (s);   /* { dg-message "length computed here" "PR122881" { xfail *-*-* } } */
+    T (d, s, n);                  /* { dg-message ".strncat\[^\n\r\]* specified bound depends on the length of the source argument" "PR122881" { xfail *-*-* } } */
   }
 }
 
diff --git a/gcc/tree-ssa-reassoc.cc b/gcc/tree-ssa-reassoc.cc
index c140f76766e..6e220e02ecd 100644
--- a/gcc/tree-ssa-reassoc.cc
+++ b/gcc/tree-ssa-reassoc.cc
@@ -5268,6 +5268,9 @@ rewrite_expr_tree (gimple *stmt, enum tree_code rhs_code, unsigned int opindex,
 
       oe1 = ops[opindex];
       oe2 = ops[opindex + 1];
+      if (commutative_tree_code (rhs_code)
+	  && tree_swap_operands_p (oe1->op, oe2->op))
+	std::swap (oe1, oe2);
 
       if (rhs1 != oe1->op || rhs2 != oe2->op)
 	{