Enable cpp code path for Categorify ops (#389)

* allow cpp code path to be used for Categorify ops

* Update merlin/systems/workflow/base.py

* formatting

* spelling

* require env-variable opt-in tfor cpp code path

* Update merlin/systems/workflow/base.py

---------

Co-authored-by: Oliver Holworthy <[email protected]>
Co-authored-by: Julio Perez <[email protected]>

merlin/systems/workflow/base.py

@@ -27,6 +27,7 @@
 import functools
 import json
 import logging
+import os
 
 from merlin.dag import ColumnSelector, DataFormats, Supports
 from merlin.dag.executors import LocalExecutor, _convert_format, _data_format
@@ -66,15 +67,24 @@ def __init__(self, workflow, output_dtypes, model_config, model_device):
             )
 
         # recurse over all column groups, initializing operators for inference pipeline.
-        # (disabled for now while we sort out whether and how we want to use C++ implementations
-        # of NVTabular operators for performance optimization)
-        # self._initialize_ops(self.workflow.output_node)
+        # (disabled everything other than operators that are specifically listed
+        # by the `NVT_CPP_OPS` environment variable while we sort out whether
+        # and how we want to use C++ implementations of NVTabular operators for
+        # performance optimization)
+        _nvt_cpp_ops = os.environ.get("NVT_CPP_OPS", "Categorify").split(",")
+        self._initialize_ops(self.workflow.output_node, restrict=_nvt_cpp_ops)
+
+    def _initialize_ops(self, workflow_node, visited=None, restrict=None):
+        restrict = restrict or []
 
-    def _initialize_ops(self, workflow_node, visited=None):
         if visited is None:
             visited = set()
 
-        if workflow_node.op and hasattr(workflow_node.op, "inference_initialize"):
+        if (
+            workflow_node.op
+            and hasattr(workflow_node.op, "inference_initialize")
+            and (not restrict or workflow_node.op.label in restrict)
+        ):
             inference_op = workflow_node.op.inference_initialize(
                 workflow_node.selector, self.model_config
             )
@@ -96,7 +106,7 @@ def _initialize_ops(self, workflow_node, visited=None):
         for parent in workflow_node.parents_with_dependencies:
             if parent not in visited:
                 visited.add(parent)
-                self._initialize_ops(parent, visited)
+                self._initialize_ops(parent, visited=visited, restrict=restrict)
 
     def run_workflow(self, input_tensors):
         transformable = TensorTable(input_tensors).to_df()