Add testcase for PR57478

From-SVN: r199531

gcc/testsuite/ChangeLog

+2013-05-31  Marek Polacek  <polacek@redhat.com>
+
+	PR tree-optimization/57478
+	PR tree-optimization/57453
+	* gcc.dg/torture/pr57478.c: New test.
+
 2013-05-31  Tobias Burnus  <burnus@net-b.de>
 
 	PR fortran/57456

gcc/testsuite/gcc.dg/torture/pr57478.c

+/* { dg-do compile } */
+
+typedef struct Node Node;
+
+struct Node
+{
+  Node *Pred, *Suc;
+  Node *SubBestPred;
+  Node *SubBestSuc;
+};
+
+void
+foo (Node *N)
+{
+  do
+    {
+      N->SubBestPred = N->Pred;
+      N->SubBestSuc = N->Suc;
+    }
+  while (N = N->Suc);
+}