Support postproc inputs to be list or dict with outputs from other postproc modules (#2733)

Summary:
Pull Request resolved: #2733

Postproc modules with collection inputs (list or dict) with non-static (derived from input or other postproc) elements were not properly rewritten - input elements remained fx.Nodes even during the actual model forward (i.e. outside rewrite, during pipeline execution)

To illustrate:

```
def forward(model_input: ...) -> ...:
    modified_input = model_input.float_features + 1
    sharded_module_input = self.postproc(model_input, modified_input)  # works
    sharded_module_input = self.postproc(model_input, [123])  # works
    sharded_module_input = self.postproc(model_input, [torch.ones_like(modified_input)])  # fails
    sharded_module_input = self.postproc(model_input, [modified_input])  # fails
    sharded_module_input = self.postproc(model_input, { 'a': 123 })  # works
    sharded_module_input = self.postproc(model_input, { 'a': torch.ones_like(modified_input) })  # fails
    sharded_module_input = self.postproc(model_input, { 'a': modified_input })  # fails

    return self.ebc(sharded_module_input)
```

Reviewed By: sarckk

Differential Revision: D69292525

fbshipit-source-id: 4ba9672f3e31248b4850ba7ff35a07d7f292bd06

Author: che-sh

torchrec/distributed/test_utils/test_model.py

@@ -1832,6 +1832,103 @@ def forward(
         return pred.sum(), pred
 
 
+class TestModelWithPreprocCollectionArgs(nn.Module):
+    """
+    Basic module with up to 3 postproc modules:
+    - postproc on idlist_features for non-weighted EBC
+    - postproc on idscore_features for weighted EBC
+    - postproc_inner on model input shared by both EBCs
+    - postproc_outer providing input to postproc_b (aka nested postproc)
+
+    Args:
+        tables,
+        weighted_tables,
+        device,
+        postproc_module_outer,
+        postproc_module_nested,
+        num_float_features,
+
+    Example:
+        >>> TestModelWithPreprocWithListArg(tables, weighted_tables, device)
+
+    Returns:
+        Tuple[torch.Tensor, torch.Tensor]
+    """
+
+    CONST_DICT_KEY = "const"
+    INPUT_TENSOR_DICT_KEY = "tensor_from_input"
+    POSTPTOC_TENSOR_DICT_KEY = "tensor_from_postproc"
+
+    def __init__(
+        self,
+        tables: List[EmbeddingBagConfig],
+        weighted_tables: List[EmbeddingBagConfig],
+        device: torch.device,
+        postproc_module_outer: nn.Module,
+        postproc_module_nested: nn.Module,
+        num_float_features: int = 10,
+    ) -> None:
+        super().__init__()
+        self.dense = TestDenseArch(num_float_features, device)
+
+        self.ebc: EmbeddingBagCollection = EmbeddingBagCollection(
+            tables=tables,
+            device=device,
+        )
+        self.weighted_ebc = EmbeddingBagCollection(
+            tables=weighted_tables,
+            is_weighted=True,
+            device=device,
+        )
+        self.postproc_nonweighted = TestPreprocNonWeighted()
+        self.postproc_weighted = TestPreprocWeighted()
+        self._postproc_module_outer = postproc_module_outer
+        self._postproc_module_nested = postproc_module_nested
+
+    def forward(
+        self,
+        input: ModelInput,
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        """
+        Runs preproc for EBC and weighted EBC, optionally runs postproc for input
+
+        Args:
+            input
+        Returns:
+            Tuple[torch.Tensor, torch.Tensor]
+        """
+        modified_input = input
+
+        outer_postproc_input = self._postproc_module_outer(modified_input)
+
+        preproc_input_list = [
+            1,
+            modified_input.float_features,
+            outer_postproc_input,
+        ]
+        preproc_input_dict = {
+            self.CONST_DICT_KEY: 1,
+            self.INPUT_TENSOR_DICT_KEY: modified_input.float_features,
+            self.POSTPTOC_TENSOR_DICT_KEY: outer_postproc_input,
+        }
+
+        modified_input = self._postproc_module_nested(
+            modified_input, preproc_input_list, preproc_input_dict
+        )
+
+        modified_idlist_features = self.postproc_nonweighted(
+            modified_input.idlist_features
+        )
+        modified_idscore_features = self.postproc_weighted(
+            modified_input.idscore_features
+        )
+        ebc_out = self.ebc(modified_idlist_features[0])
+        weighted_ebc_out = self.weighted_ebc(modified_idscore_features[0])
+
+        pred = torch.cat([ebc_out.values(), weighted_ebc_out.values()], dim=1)
+        return pred.sum(), pred
+
+
 class TestNegSamplingModule(torch.nn.Module):
     """
     Basic module to simulate feature augmentation postproc (e.g. neg sampling) for testing

torchrec/distributed/train_pipeline/tests/test_train_pipelines.py

@@ -13,14 +13,15 @@
 from contextlib import ExitStack
 from dataclasses import dataclass
 from functools import partial
-from typing import cast, List, Optional, Tuple, Type, Union
+from typing import cast, Dict, List, Optional, Tuple, Type, Union
 from unittest.mock import MagicMock
 
 import torch
 from hypothesis import given, settings, strategies as st, Verbosity
 from torch import nn, optim
 from torch._dynamo.testing import reduce_to_scalar_loss
 from torch._dynamo.utils import counters
+from torch.fx._symbolic_trace import is_fx_tracing
 from torchrec.distributed import DistributedModelParallel
 from torchrec.distributed.embedding_types import EmbeddingComputeKernel
 from torchrec.distributed.embeddingbag import EmbeddingBagCollectionSharder
@@ -36,6 +37,7 @@
     ModelInput,
     TestEBCSharder,
     TestModelWithPreproc,
+    TestModelWithPreprocCollectionArgs,
     TestNegSamplingModule,
     TestPositionWeightedPreprocModule,
     TestSparseNN,
@@ -1448,6 +1450,81 @@ def forward(
         self.assertEqual(len(pipeline._pipelined_modules), 2)
         self.assertEqual(len(pipeline._pipelined_postprocs), 1)
 
+    # pyre-ignore
+    @unittest.skipIf(
+        not torch.cuda.is_available(),
+        "Not enough GPUs, this test requires at least one GPU",
+    )
+    def test_pipeline_postproc_with_collection_args(self) -> None:
+        """
+        Exercises scenario when postproc module has an argument that is a list or dict
+        with some elements being:
+            * static scalars
+            * static tensors (e.g. torch.ones())
+            * tensors derived from input batch (e.g. input.idlist_features["feature_0"])
+            * tensors derived from input batch and other postproc module (e.g. other_postproc(input.idlist_features["feature_0"]))
+        """
+        test_runner = self
+
+        class PostprocOuter(nn.Module):
+            def __init__(
+                self,
+            ) -> None:
+                super().__init__()
+
+            def forward(
+                self,
+                model_input: ModelInput,
+            ) -> torch.Tensor:
+                return model_input.float_features * 0.1
+
+        class PostprocInner(nn.Module):
+            def __init__(
+                self,
+            ) -> None:
+                super().__init__()
+
+            def forward(
+                self,
+                model_input: ModelInput,
+                input_list: List[Union[torch.Tensor, int]],
+                input_dict: Dict[str, Union[torch.Tensor, int]],
+            ) -> ModelInput:
+                if not is_fx_tracing():
+                    for idx, value in enumerate(input_list):
+                        if isinstance(value, torch.fx.Node):
+                            test_runner.fail(
+                                f"input_list[{idx}] was a fx.Node: {value}"
+                            )
+                        model_input.float_features += value
+
+                    for key, value in input_dict.items():
+                        if isinstance(value, torch.fx.Node):
+                            test_runner.fail(
+                                f"input_dict[{key}] was a fx.Node: {value}"
+                            )
+                        model_input.float_features += value
+
+                return model_input
+
+        model = TestModelWithPreprocCollectionArgs(
+            tables=self.tables[:-1],  # ignore last table as postproc will remove
+            weighted_tables=self.weighted_tables[:-1],  # ignore last table
+            device=self.device,
+            postproc_module_outer=PostprocOuter(),
+            postproc_module_nested=PostprocInner(),
+        )
+
+        pipelined_model, pipeline = self._check_output_equal(
+            model,
+            self.sharding_type,
+        )
+
+        # both EC end EBC are pipelined
+        self.assertEqual(len(pipeline._pipelined_modules), 2)
+        # both outer and nested postproces are pipelined
+        self.assertEqual(len(pipeline._pipelined_postprocs), 4)
+
 
 class EmbeddingTrainPipelineTest(TrainPipelineSparseDistTestBase):
     @unittest.skipIf(