revert change for rowData

Author: kiszk

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/generators.scala

@@ -199,7 +199,8 @@ case class Stack(children: Seq[Expression]) extends Generator {
 
   override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
     // Rows - we write these into an array.
-    val rowData = ctx.freshName("rowsStack")
+    val rowData = ctx.addMutableState("InternalRow[]", "rows",
+      v => s"$v = new InternalRow[$numRows];")
     val values = children.tail
     val dataTypes = values.take(numFields).map(_.dataType)
     val code = ctx.splitExpressionsWithCurrentInputs(Seq.tabulate(numRows) { row =>
@@ -215,7 +216,6 @@ case class Stack(children: Seq[Expression]) extends Generator {
     val wrapperClass = classOf[mutable.WrappedArray[_]].getName
     ev.copy(code =
       s"""
-         |InternalRow[] $rowData = new InternalRow[$numRows];
          |$code
          |$wrapperClass<InternalRow> ${ev.value} = $wrapperClass$$.MODULE$$.make($rowData);
        """.stripMargin, isNull = "false")