[GitHub] [spark] cloud-fan commented on a change in pull request #29975: [SPARK-33092][SQL] Support subexpression elimination in ProjectExec

[GitBox <gi...@apache.org>]

cloud-fan commented on a change in pull request #29975:
URL: https://github.com/apache/spark/pull/29975#discussion_r501472070



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File path: sql/core/src/main/scala/org/apache/spark/sql/execution/basicPhysicalOperators.scala
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@@ -66,10 +66,22 @@ case class ProjectExec(projectList: Seq[NamedExpression], child: SparkPlan)
 
   override def doConsume(ctx: CodegenContext, input: Seq[ExprCode], row: ExprCode): String = {
     val exprs = bindReferences[Expression](projectList, child.output)
-    val resultVars = exprs.map(_.genCode(ctx))
+    val (subExprsCode, resultVars) = if (conf.subexpressionEliminationEnabled) {
+      // subexpression elimination
+      val subExprs = ctx.subexpressionEliminationForWholeStageCodegen(exprs)
+      val genVars = ctx.withSubExprEliminationExprs(subExprs.states) {
+        exprs.map(_.genCode(ctx))
+      }
+      (subExprs.codes.mkString("\n"), genVars)
+    } else {
+      ("", exprs.map(_.genCode(ctx)))
+    }
+
     // Evaluation of non-deterministic expressions can't be deferred.
     val nonDeterministicAttrs = projectList.filterNot(_.deterministic).map(_.toAttribute)
     s"""

Review comment:
       can you give an example of this part of code for the query in https://issues.apache.org/jira/browse/SPARK-32989 ?




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