op.clear();
  private OPT_BURS_TreeNode buildTree(OPT_Instruction s) {        OPT_BURS_TreeNode root = new OPT_BURS_TreeNode(new OPT_DepGraphNode(s));    OPT_BURS_TreeNode cur = root;    for (OPT_OperandEnumeration uses = s.getUses(); uses.hasMoreElements();) {      OPT_Operand op = uses.next();      if (op == null) continue;      op.clear();      // Set child = OPT_BURS_TreeNode for operand op      OPT_BURS_TreeNode child;      if (op instanceof OPT_RegisterOperand) {        if (op.asRegister().register.isValidation()) continue;        child = Register;       } else if (op instanceof OPT_IntConstantOperand) {        child = new OPT_BURS_IntConstantTreeNode(((OPT_IntConstantOperand)op).value);      } else if (op instanceof OPT_LongConstantOperand) {        child = LongConstant;      } else if (op instanceof OPT_AddressConstantOperand) {        child = AddressConstant;      } else if (op instanceof OPT_BranchOperand && s.isCall()) {        child = BranchTarget;      //-#if RVM_WITH_OSR      } else if (op instanceof OPT_InlinedOsrTypeInfoOperand && s.isYieldPoint()) {        child = NullTreeNode;      //-#endif       } else {        continue;      }      // Attach child as child of cur_parent in correct position      if (cur.child1 == null) {        cur.child1 = child;       } else if (cur.child2 == null) {        cur.child2 = child;       } else {        // Create auxiliary node so as to represent        // a instruction with arity > 2 in a binary tree.        OPT_BURS_TreeNode child1 = cur.child2;        OPT_BURS_TreeNode aux = new OPT_BURS_TreeNode(OTHER_OPERAND_opcode);        cur.child2 = aux;        cur = aux;        cur.child1 = child1;        cur.child2 = child;      }    }    // patch for calls & return     switch (s.getOpcode()) {    case CALL_opcode:    case SYSCALL_opcode:    //-#if RVM_WITH_OSR    case YIELDPOINT_OSR_opcode:    //-#endif      if (cur.child2 == null)        cur.child2 = NullTreeNode;      // fall through    case RETURN_opcode:      if (cur.child1 == null)        cur.child1 = NullTreeNode;    }    return root;  }