--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/gcc.dg/pr50763-2.c	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,46 @@
+/* { dg-do compile } */
+/* { dg-options "-O2" } */
+
+typedef union tree_node *tree;
+
+struct tree_base
+{
+  int code;
+};
+
+struct tree_typed
+{
+  struct tree_base base;
+  tree type;
+};
+
+struct tree_common
+{
+  struct tree_typed typed;
+};
+
+struct tree_type_common
+{
+  tree main_variant;
+};
+
+union tree_node
+{
+  struct tree_base base;
+  struct tree_typed typed;
+  struct tree_type_common type_common;
+};
+
+int std_canonical_va_list_type (tree type)
+{
+  if (type->base.code)
+    type = type->typed.type;
+  else
+    if (type->typed.type->base.code)
+      type = type->typed.type;
+
+  if (type->type_common.main_variant)
+    return 1;
+
+  return 0;
+}