[PATCH] Add testcase for PR57478

[Marek Polacek]

This adds a reduced testcase for PR57478.
Regtested on x86_64-linux.  Ok for trunk?

2013-05-31  Marek Polacek  <pola...@redhat.com>

        PR tree-optimization/57478
        PR tree-optimization/57453
        * gcc.dg/torture/pr57478.c: New test.

--- gcc/testsuite/gcc.dg/torture/pr57478.c.mp2  2013-05-31 11:31:27.179683480 
+0200
+++ gcc/testsuite/gcc.dg/torture/pr57478.c      2013-05-31 11:31:50.239753729 
+0200
@@ -0,0 +1,21 @@
+/* { 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);
+}

        Marek