[GitHub] [incubator-daffodil] bsloane1650 commented on a change in pull request #316: Assortment of changes to improve performance

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bsloane1650 commented on a change in pull request #316: Assortment of changes to improve performance
URL: https://github.com/apache/incubator-daffodil/pull/316#discussion_r370350257
 
 

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 File path: daffodil-runtime1/src/main/scala/org/apache/daffodil/processors/Evaluatable.scala
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 @@ -285,7 +285,17 @@ abstract class Evaluatable[+T <: AnyRef](protected val ci: DPathCompileInfo, qNa
   /**
    * Preferred for use in the runtime.
    */
-  @inline final def maybeConstant = constValue_.asInstanceOf[Maybe[T]]
+  @inline final def maybeConstant = {
+    // We could just do constValue_.asInstanceOf[Maybe[T]], but the compiled
+    // bytecode ends up allocating a Maybe. Since constant values are accessed
+    // very often, we really want to avoid that overhead. The following gets
+    // rid of those unnecessary allocations.
+    if (constValue_.isDefined) {
+      Maybe[T](constValue_.get.asInstanceOf[T])
 
 Review comment:
   When I was working on the DataValues class, I got into a workflow, where I would look dissassembly all the *.class files and look for allocations of DataValue. I also did a similar trick when I was looking for scala.lang.BigInt/BigDecimal.
   
   It is probably more work then it is worth to do this in an automated fashion (particularly because removing all boxing would likely be a lot more effort then it is worth), however, it might be worth doing this as a one off. Possibly also document the process on the wiki and repeat it manually on occasion.
   
   

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