public List<ExprNodeGenericFuncDesc> getLLFuncExprsInTopExpr(ExprNodeDesc topExpr) {
    if (mapTopExprToLLFunExprs == null) {
      return null;
    }
    return mapTopExprToLLFunExprs.get(topExpr);
  }
map from the Select Expr Node to the LL Function invocations in it.
ql/src/java/org/apache/hadoop/hive/ql/parse/LeadLagInfo.java