presto-main/src/main/java/io/prestosql/memory/TraversingQueryContextVisitor.java/TraversingQueryContextVisitor/visitPipelineContext
class TraversingQueryContextVisitor:    @Override
    public R visitPipelineContext(PipelineContext pipelineContext, C visitContext)
    {
        return mergeResults(pipelineContext.acceptChildren(this, visitContext));
    }