public ExprInfo addOrGetExprInfo(ExprNodeDesc expr) {
    ExprInfo exprInfo = exprInfoMap.get(expr);
    if (exprInfo == null) {
      exprInfo = new ExprInfo();
      exprInfoMap.put(expr, exprInfo);
    }
    return exprInfo;
  }
Get additional info for a given expression node if it
exists, or create a new one and store it if it does not
ql/src/java/org/apache/hadoop/hive/ql/ppd/ExprWalkerInfo.java