Github user maropu commented on a diff in the pull request:

    https://github.com/apache/spark/pull/18931#discussion_r136710824
  
    --- Diff: 
sql/core/src/main/scala/org/apache/spark/sql/execution/WholeStageCodegenExec.scala
 ---
    @@ -149,14 +149,146 @@ trait CodegenSupport extends SparkPlan {
     
         ctx.freshNamePrefix = parent.variablePrefix
         val evaluated = evaluateRequiredVariables(output, inputVars, 
parent.usedInputs)
    +
    +    // Under certain conditions, we can put the logic to consume the rows 
of this operator into
    +    // another function. So we can prevent a generated function too long 
to be optimized by JIT.
    +    // The conditions:
    +    // 1. The parent uses all variables in output. we can't defer variable 
evaluation when consume
    +    //    in another function.
    +    // 2. The output variables are not empty. If it's empty, we don't 
bother to do that.
    +    // 3. We don't use row variable. The construction of row uses deferred 
variable evaluation. We
    +    //    can't do it.
    +    // 4. The number of output variables must less than maximum number of 
parameters in Java method
    +    //    declaration.
    +    val requireAllOutput = output.forall(parent.usedInputs.contains(_))
    +    val consumeFunc =
    +      if (row == null && outputVars.nonEmpty && requireAllOutput && 
outputVars.length < 255) {
    +        constructDoConsumeFunction(ctx, inputVars)
    --- End diff --
    
    We always split consume functions?; we don't need to check if this consume 
function is too long?


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