Github user kiszk commented on a diff in the pull request:
https://github.com/apache/spark/pull/19728#discussion_r150444269
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/stringExpressions.scala
---
@@ -63,15 +63,26 @@ case class Concat(children: Seq[Expression]) extends
Expression with ImplicitCas
override protected def doGenCode(ctx: CodegenContext, ev: ExprCode):
ExprCode = {
val evals = children.map(_.genCode(ctx))
- val inputs = evals.map { eval =>
- s"${eval.isNull} ? null : ${eval.value}"
- }.mkString(", ")
- ev.copy(evals.map(_.code).mkString("\n") + s"""
- boolean ${ev.isNull} = false;
- UTF8String ${ev.value} = UTF8String.concat($inputs);
- if (${ev.value} == null) {
- ${ev.isNull} = true;
+ val argNums = evals.length
+ val args = ctx.freshName("argLen")
+ ctx.addMutableState("UTF8String[]", args, "")
+
+ val inputs = evals.zipWithIndex.map { case (eval, index) =>
+ if (eval.isNull != "true") {
--- End diff --
If `eval.isNull` is not a pre-evaluated constant, I expect that the
following code at lines 73-74 will be generated. Only when we ensure it is
`true`, we can avoid assigning a value (use default `null` value).
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