add an assert, patch by Daniel Berlin

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25343 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Analysis/ET-Forest.h

@@ -50,6 +50,7 @@ public:
     Depth(0), Min(0), MinOccurrence(this) {};
 
   void setParent(ETOccurrence *n) {
+    assert(n != this && "Trying to set parent to ourselves");
     Parent = n;
   }