PERFORMANCE: Avoid redundant dataset clear calls

Fixes #9294

config/jvm.options

@@ -75,3 +75,6 @@
 
 # Entropy source for randomness
 -Djava.security.egd=file:/dev/urandom
+-agentlib:jdwp=transport=dt_socket,server=n,address=localhost:5006,suspend=y
+-Dorg.codehaus.janino.source_debugging.dir=/Users/brownbear/src/logstash/logs/debug
+-Dorg.codehaus.janino.source_debugging.enable=true

logstash-core/src/main/java/org/logstash/config/ir/compiler/ClassFields.java

@@ -10,11 +10,9 @@ import java.util.stream.Collectors;
  */
 final class ClassFields {
 
-    private final Collection<FieldDefinition> definitions;
+    private final Collection<FieldDefinition> definitions = new ArrayList<>();
 
-    ClassFields() {
-        definitions = new ArrayList<>();
-    }
+    private final Collection<Closure> afterInit = new ArrayList<>();
 
     /**
      * Add a field of given type that is initialized by the given {@link SyntaxElement} that will
@@ -48,6 +46,14 @@ final class ClassFields {
         return addField(FieldDefinition.mutableUnassigned(definitions.size(), type));
     }
 
+    public void addAfterInit(final Closure closure) {
+        afterInit.add(closure);
+    }
+
+    public Closure afterInit() {
+        return Closure.wrap(afterInit.toArray(new Closure[0]));
+    }
+
     /**
      * Returns the subset of fields that are assigned in the constructor.
      * @return Subset of fields to be assigned by the constructor

logstash-core/src/main/java/org/logstash/config/ir/compiler/ComputeStepSyntaxElement.java

@@ -204,7 +204,10 @@ public final class ComputeStepSyntaxElement<T extends Dataset> implements Syntax
                 ctor.add(argVar);
             }
         }
-        return combine(ctorFields, MethodSyntaxElement.constructor(name, constructor, ctor));
+        return combine(
+            ctorFields,
+            MethodSyntaxElement.constructor(name, constructor.add(fields.afterInit()), ctor)
+        );
     }
 
     /**

logstash-core/src/main/java/org/logstash/config/ir/compiler/DatasetCompiler.java

@@ -72,9 +72,21 @@ public final class DatasetCompiler {
         final ValueSyntaxElement elseData = fields.add(RubyArray.class, arrayInit);
         final ValueSyntaxElement buffer = fields.add(RubyArray.class, arrayInit);
         final ValueSyntaxElement done = fields.add(boolean.class);
+        final ValueSyntaxElement right = fields.add(DatasetCompiler.Complement.class);
         final VariableDefinition event =
             new VariableDefinition(JrubyEventExtLibrary.RubyEvent.class, "event");
         final ValueSyntaxElement eventVal = event.access();
+        fields.addAfterInit(
+            Closure.wrap(
+                SyntaxFactory.assignment(right,
+                    SyntaxFactory.cast(
+                        DatasetCompiler.Complement.class, SyntaxFactory.constant(
+                            DatasetCompiler.class, DatasetCompiler.Complement.class.getSimpleName()
+                        ).call("from", SyntaxFactory.THIS, elseData)
+                    )
+                )
+            )
+        );
         return new ComputeStepSyntaxElement<>(
             Arrays.asList(
                 MethodSyntaxElement.compute(
@@ -96,10 +108,15 @@ public final class DatasetCompiler {
                         .add(SyntaxFactory.ret(ifData))
                 ),
                 MethodSyntaxElement.clear(
-                    clearSyntax(parentFields).add(clear(ifData)).add(clear(elseData))
-                        .add(SyntaxFactory.assignment(done, SyntaxFactory.FALSE))
+                    Closure.wrap(
+                        SyntaxFactory.ifCondition(
+                            done,
+                            clearSyntax(parentFields).add(clear(ifData)).add(clear(elseData))
+                                .add(SyntaxFactory.assignment(done, SyntaxFactory.FALSE))
+                        )
+                    )
                 ),
-                MethodSyntaxElement.right(elseData)
+                MethodSyntaxElement.right(right)
             ), fields, SplitDataset.class
         );
     }
@@ -150,8 +167,13 @@ public final class DatasetCompiler {
             body.add(SyntaxFactory.assignment(done, SyntaxFactory.TRUE))
                 .add(SyntaxFactory.ret(outputBuffer)),
             Closure.wrap(
-                clearSyntax(parentFields), clear(outputBuffer),
-                SyntaxFactory.assignment(done, SyntaxFactory.FALSE)
+                SyntaxFactory.ifCondition(
+                    done,
+                    Closure.wrap(
+                        clearSyntax(parentFields), clear(outputBuffer),
+                        SyntaxFactory.assignment(done, SyntaxFactory.FALSE)
+                    )
+                )
             ), fields
         );
     }
@@ -420,8 +442,10 @@ public final class DatasetCompiler {
 
         @Override
         public void clear() {
-            parent.clear();
-            done = false;
+            if (done) {
+                parent.clear();
+                done = false;
+            }
         }
     }
 }

logstash-core/src/main/java/org/logstash/config/ir/compiler/MethodSyntaxElement.java

@@ -55,13 +55,7 @@ interface MethodSyntaxElement extends SyntaxElement {
      */
     static MethodSyntaxElement right(final ValueSyntaxElement elseData) {
         return new MethodSyntaxElement.MethodSyntaxElementImpl(Dataset.class, "right",
-            Closure.wrap(
-                SyntaxFactory.ret(
-                    SyntaxFactory.constant(
-                        DatasetCompiler.class, DatasetCompiler.Complement.class.getSimpleName()
-                    ).call("from", SyntaxFactory.THIS, elseData)
-                )
-            )
+            Closure.wrap(SyntaxFactory.ret(elseData))
         );
     }