support scripting for torchscript ExportMethod

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/118

This diff adds the proper support for using scripting when exporting model.

Rename tracing-related code:
- Previously `trace_and_save_torchscript` is the primary function to export model, replace it with `export_optimize_and_save_torchscript`.
- Also rename `D2 (https://github.com/facebookresearch/d2go/commit/7992f91324aee6ae59795063a007c6837e60cdb8)TorchscriptTracingExport` to `TracingAdaptedTorchscriptExport` since it's not only for tracing now.

Introduce `jit_mode`:
- Add `jit_mode` option as the `export_kwargs` of ExportMethod.
- Add `scripting` and `tracing` trigger words to overwrite `jit_mode`. Please note that the `tracing` now applies to all models, which is different from the previous meaning (using `TracingAdapter` for RCNN).
- Therefore there're two ways of using scripting mode, 1) setting `jit_mode` in prepare_for_export; 2) using `script` trigger words. Add unit test as examples to illustrate two ways.
- Don't use `TracingAdapter` when scripting since it's not scriptable.

Consolidate triggering words logic.
- Group logic of handling trigger words (eg. `_mobile`, `_int8`, `scripting`, `tracing`) into a single decorator `update_export_kwargs_from_export_method` for better structuring and readability.

Reviewed By: zhanghang1989

Differential Revision: D31181624

fbshipit-source-id: 5fbb0d4fa4c29ffa4a761af8ea8f93b4bad4cef9

d2go/export/torchscript.py

@@ -5,7 +5,7 @@
 import contextlib
 import logging
 import os
-from typing import Tuple, Optional, Dict, NamedTuple, List, AnyStr, Set
+from typing import Any, Tuple, Optional, Dict, NamedTuple, List, AnyStr, Set
 
 import torch
 from d2go.export.api import ModelExportMethodRegistry, ModelExportMethod
@@ -24,6 +24,7 @@ from torch.utils.mobile_optimizer import optimize_for_mobile
 logger = logging.getLogger(__name__)
 
 TORCHSCRIPT_FILENAME_KEY: str = "torchscript_filename"
+DEFAULT_JIT_MODE = "trace"
 
 
 class MobileOptimizationConfig(NamedTuple):
@@ -34,23 +35,54 @@ class MobileOptimizationConfig(NamedTuple):
     torchscript_filename: str = "mobile_optimized.ptl"
 
 
-def trace_and_save_torchscript(
+def export_optimize_and_save_torchscript(
     model: nn.Module,
-    inputs: Tuple[torch.Tensor],
+    inputs: Optional[Tuple[Any]],
     output_path: str,
+    *,
+    jit_mode: Optional[str] = DEFAULT_JIT_MODE,
     torchscript_filename: str = "model.jit",
     mobile_optimization: Optional[MobileOptimizationConfig] = None,
     _extra_files: Optional[Dict[str, bytes]] = None,
-):
-    logger.info("Tracing and saving TorchScript to {} ...".format(output_path))
+) -> str:
+    """
+    The primary function for exporting PyTorch model to TorchScript.
+
+    Args:
+        model (nn.Module): the model to export. When given a ScriptModule, skip the export
+            and only optimize and save model.
+        inputs (tuple or None): input arguments of model, can be called as model(*inputs).
+            Will not be used when scripting the model.
+        output_path (str): directory that the model will be saved.
+        jit_mode (str): trace/script or None if the model is already a ScriptModule.
+        torchscript_filename (str): the filename of non-mobile-optimized model.
+        mobile_optimization (MobileOptimizationConfig): when provided, the mobile optimization
+            will be applied.
+        _extra_files (Dict[str, bytes]): when provided, extra files will be saved.
+
+    Returns:
+        (str): filename of the final model no matter optmized or not.
+    """
+
+    logger.info("Export, optimize and saving TorchScript to {} ...".format(output_path))
     PathManager.mkdirs(output_path)
     if _extra_files is None:
         _extra_files = {}
 
+    if isinstance(model, torch.jit.ScriptModule):
+        if jit_mode is not None:
+            logger.info("The input model is already a ScriptModule, skip the jit step")
+    elif jit_mode == "trace":
+        logger.info("Tracing the model ...")
         with torch.no_grad():
             script_model = torch.jit.trace(model, inputs)
+    elif jit_mode == "script":
+        logger.info("Scripting the model ...")
+        script_model = torch.jit.script(model)
+    else:
+        raise ValueError("Unsupported jit_mode: {}".format(jit_mode))
 
-    with make_temp_directory("trace_and_save_torchscript") as tmp_dir:
+    with make_temp_directory("export_optimize_and_save_torchscript") as tmp_dir:
 
         @contextlib.contextmanager
         def _synced_local_file(rel_path):
@@ -100,6 +132,26 @@ def trace_and_save_torchscript(
         return torchscript_filename
 
 
+# For backward compatibility, TODO: remove this function.
+def trace_and_save_torchscript(
+    model: nn.Module,
+    inputs: Optional[Tuple[Any]],
+    output_path: str,
+    torchscript_filename: str = "model.jit",
+    mobile_optimization: Optional[MobileOptimizationConfig] = None,
+    _extra_files: Optional[Dict[str, bytes]] = None,
+):
+    return export_optimize_and_save_torchscript(
+        model,
+        inputs,
+        output_path,
+        jit_mode="trace",
+        torchscript_filename=torchscript_filename,
+        mobile_optimization=mobile_optimization,
+        _extra_files=_extra_files,
+    )
+
+
 class TorchscriptWrapper(nn.Module):
     """ """
 
@@ -140,14 +192,14 @@ def tracing_adapter_wrap_export(old_f):
         force_disable_tracing_adapter = export_kwargs.pop(
             "force_disable_tracing_adapter", False
         )
-        if force_disable_tracing_adapter:
+        is_trace_mode = export_kwargs.get("jit_mode", "trace") == "trace"
+        if force_disable_tracing_adapter or not is_trace_mode:
             logger.info("Not trace mode, export normally")
             return old_f(
                 cls, model, input_args, save_path, export_method, **export_kwargs
             )
 
         if _is_data_flattened_tensors(input_args):
-            # TODO: only dry-run for traceing
             logger.info("Dry run the model to check if TracingAdapter is needed ...")
             outputs = model(*input_args)
             if _is_data_flattened_tensors(outputs):
@@ -178,7 +230,7 @@ def tracing_adapter_wrap_export(old_f):
             adapter.flattened_inputs,
             save_path,
             export_method,
-            **export_kwargs
+            **export_kwargs,
         )
         inputs_schema = dump_dataclass(adapter.inputs_schema)
         outputs_schema = dump_dataclass(adapter.outputs_schema)
@@ -231,19 +283,20 @@ def tracing_adapter_wrap_load(old_f):
     return new_f
 
 
-class DefaultTorchscriptExport(ModelExportMethod):
-    @classmethod
-    def export(
-        cls,
-        model: nn.Module,
-        input_args: Tuple[Tuple[torch.Tensor]],
-        save_path: str,
-        export_method: Optional[str],
-        **export_kwargs
-    ):
+def update_export_kwargs_from_export_method(old_f):
+    """
+    Provide some convenient way of updating export_kwargs by adding trigger words in
+    `export_method`. For example, instead of setting `mobile_optimization` in the
+    model_export_kwargs of the PredictorExportConfig, user can simply put the `_mobile`
+    trigger word in the --predictor-type (which will then be forwarded as `export_method`
+    in most cases) to enable mobile optimizaiton.
+    """
+
+    def new_f(cls, model, input_args, save_path, export_method, **export_kwargs):
         if export_method is not None:
-            # update export_kwargs based on export_method
             assert isinstance(export_method, str)
+            original_export_method = export_method
+
             if "_mobile" in export_method:
                 if "mobile_optimization" in export_kwargs:
                     logger.warning(
@@ -251,8 +304,56 @@ class DefaultTorchscriptExport(ModelExportMethod):
                     )
                 else:
                     export_kwargs["mobile_optimization"] = MobileOptimizationConfig()
+                export_method = export_method.replace("_mobile", "", 1)
 
-        torchscript_filename = trace_and_save_torchscript(
+            if "@scripting" in export_method:
+                jit_mode = export_kwargs.get("jit_mode", None)
+                if jit_mode and jit_mode != "script":
+                    logger.warning(
+                        "`jit_mode` is already specified as {}, overwrite it to `script`"
+                        " since @scripting appears in export_method".format(jit_mode)
+                    )
+                export_kwargs["jit_mode"] = "script"
+                export_method = export_method.replace("@scripting", "", 1)
+
+            if "@tracing" in export_method:
+                jit_mode = export_kwargs.get("jit_mode", None)
+                if jit_mode and jit_mode != "trace":
+                    logger.warning(
+                        "`jit_mode` is already specified as {}, overwrite it to `trace`"
+                        " since @tracing appears in export_method".format(jit_mode)
+                    )
+                export_kwargs["jit_mode"] = "trace"
+                export_method = export_method.replace("@tracing", "", 1)
+
+            if "_int8" in export_method:
+                export_method = export_method.replace("_int8", "", 1)
+
+            if export_method != "torchscript":
+                logger.warning(
+                    "Suspcious export_method after removing triggering words,"
+                    " original export_method: {}, remaining: {}".format(
+                        original_export_method, export_method
+                    )
+                )
+
+        return old_f(cls, model, input_args, save_path, export_method, **export_kwargs)
+
+    return new_f
+
+
+class DefaultTorchscriptExport(ModelExportMethod):
+    @classmethod
+    @update_export_kwargs_from_export_method
+    def export(
+        cls,
+        model: nn.Module,
+        input_args: Tuple[Tuple[torch.Tensor]],
+        save_path: str,
+        export_method: Optional[str],
+        **export_kwargs,
+    ):
+        torchscript_filename = export_optimize_and_save_torchscript(
             model, input_args, save_path, **export_kwargs
         )
         return {TORCHSCRIPT_FILENAME_KEY: torchscript_filename}
@@ -267,8 +368,17 @@ class DefaultTorchscriptExport(ModelExportMethod):
 @ModelExportMethodRegistry.register("torchscript_int8")
 @ModelExportMethodRegistry.register("torchscript_mobile")
 @ModelExportMethodRegistry.register("torchscript_mobile_int8")
-class D2TorchscriptTracingExport(DefaultTorchscriptExport):
+@ModelExportMethodRegistry.register("torchscript@scripting")
+@ModelExportMethodRegistry.register("torchscript_int8@scripting")
+@ModelExportMethodRegistry.register("torchscript_mobile@scripting")
+@ModelExportMethodRegistry.register("torchscript_mobile_int8@scripting")
+@ModelExportMethodRegistry.register("torchscript@tracing")
+@ModelExportMethodRegistry.register("torchscript_int8@tracing")
+@ModelExportMethodRegistry.register("torchscript_mobile@tracing")
+@ModelExportMethodRegistry.register("torchscript_mobile_int8@tracing")
+class TracingAdaptedTorchscriptExport(DefaultTorchscriptExport):
     @classmethod
+    @update_export_kwargs_from_export_method
     @tracing_adapter_wrap_export
     def export(cls, model, input_args, save_path, export_method, **export_kwargs):
         with patch_builtin_len():

d2go/modeling/meta_arch/rcnn.py

@@ -369,7 +369,7 @@ class D2RCNNInferenceWrapper(nn.Module):
     def forward(self, image):
         """
         This function describes what happends during the tracing. Note that the output
-        contains non-tensor, therefore the D2TorchscriptTracingExport must be used in
+        contains non-tensor, therefore the TracingAdaptedTorchscriptExport must be used in
         order to convert the output back from flattened tensors.
         """
         inputs = [{"image": image}]