private static RexNode getRexNodeCached(ASTNode node, RowResolver input,
      TypeCheckCtx tcCtx) throws SemanticException {
    Preconditions.checkNotNull(tcCtx.getUnparseTranslator());
    ColumnInfo colInfo = input.getExpression(node);
    if (colInfo != null) {
      ASTNode source = input.getExpressionSource(node);
      if (source != null) {
        tcCtx.getUnparseTranslator().addCopyTranslation(node, source);
      }
      return RexNodeTypeCheck.toExprNode(colInfo, input, 0, tcCtx.getRexBuilder());
    }
    return null;
  }
Find RexNode for the expression cached in the RowResolver. Returns null if not exists.
ql/src/java/org/apache/hadoop/hive/ql/parse/CalcitePlanner.java