[Training] Unifying Preprocess + Postprocessing logic for Train/Oneshot (#1212)

Order of reviews:
#1206
#1207
#1209
#1212  <-- Here
#1214

SUMMARY:
* Move the preprocessing and postprocessing logic out of
`src/llmcompressor/transformers/finetune/text_generation.py` and into
`src/llmcompressor/entrypoints/utils.py`

TEST PLAN:
Pass tests

Author: George

src/llmcompressor/entrypoints/__init__.py

@@ -1,2 +1,3 @@
 # flake8: noqa
 from .oneshot import Oneshot, oneshot
+from .utils import post_process, pre_process

src/llmcompressor/entrypoints/oneshot.py

@@ -1,21 +1,12 @@
-from pathlib import PosixPath
 from typing import Optional
 
-from loguru import logger
 from torch.utils.data import DataLoader
 from transformers import PreTrainedModel
 
 from llmcompressor.args import parse_args
 from llmcompressor.core.session_functions import active_session
 from llmcompressor.datasets import get_calibration_dataloader
-from llmcompressor.transformers.finetune.text_generation import (
-    initialize_model_from_path,
-    initialize_processor_from_path,
-)
-from llmcompressor.transformers.sparsification.compressed_tensors_utils import (
-    modify_save_pretrained,
-    patch_tied_tensors_bug,
-)
+from llmcompressor.entrypoints.utils import post_process, pre_process
 
 __all__ = ["Oneshot", "oneshot"]
 
@@ -71,7 +62,7 @@ class Oneshot:
             Initializes the `Oneshot` object by parsing input arguments, performing
             preprocessing, and setting instance attributes.
 
-        run(**kwargs):
+        __call__(**kwargs):
             Performs the one-shot calibration process by preparing a calibration
             dataloader, applying recipe modifiers to the model, and executing
             postprocessing steps.
@@ -86,17 +77,6 @@ class Oneshot:
             defined in the recipe. Each action is executed via the global
             `CompressionSession`.
 
-        _pre_process():
-            Handles preprocessing steps, including model initialization,
-            tokenizer/processor setup, and resolving tied embedding issues.
-
-        check_tied_embeddings():
-            Logs a warning if `tie_word_embeddings=True`, which may interfere with
-            saving in the one-shot workflow.
-
-        _post_process():
-            Executes postprocessing steps such as saving the model and resetting
-            lifecycle actions, especially when a custom `output_dir` is specified.
     """
 
     def __init__(
@@ -151,7 +131,7 @@ def from_args(
 
         # only run for the first oneshot call
         if do_preprocess:
-            instance._pre_process()
+            pre_process(model_args)
 
         # Set instance attributes
         instance.model = instance.model_args.model
@@ -172,7 +152,7 @@ def __call__(self):
         """
         # TODO: move back once stage runner is removed
         # Preprocess the model and tokenizer/processor
-        self._pre_process()
+        pre_process(self.model_args)
         self.model = self.model_args.model
         self.recipe = self.recipe_args.recipe
         self.processor = self.model_args.processor
@@ -183,24 +163,7 @@ def __call__(self):
         self.apply_recipe_modifiers(
             calibration_dataloader=calibration_dataloader,
         )
-        self._post_process()
-
-    def save(self):
-        """
-        Saves the model and tokenizer/processor to the output directory.
-
-        The model is saved in a compressed format if specified in `model_args`.
-        The tokenizer or processor, if available, is also saved.
-
-        Raises:
-            ValueError: If saving fails due to an invalid `output_dir` or other issues.
-        """
-        self.model.save_pretrained(
-            self.output_dir,
-            save_compressed=self.model_args.save_compressed,
-        )
-        if self.processor is not None:
-            self.processor.save_pretrained(self.output_dir)
+        post_process(model_args=self.model_args, output_dir=self.output_dir)
 
     def apply_recipe_modifiers(
         self,
@@ -236,75 +199,6 @@ def apply_recipe_modifiers(
         session.initialize(**session_kwargs)
         session.finalize(**session_kwargs)
 
-    def _pre_process(self):
-        """
-        Prepares the model and tokenizer/processor for calibration.
-
-        - Initializes the model if it's specified as a path or string.
-        - Applies patches to fix tied tensor issues and modifies `save_pretrained`
-          behavior.
-        - Initializes the processor if specified as a path or `None`.
-        - Sets the minimum tokens per module if `dataset_args` are provided.
-
-        Raises:
-            FileNotFoundError: If the model or processor path is invalid.
-        """
-        self.check_tied_embeddings()
-
-        # Initialize model
-        if isinstance(self.model_args.model, (str, PosixPath)):
-            self.model_args.model, _ = initialize_model_from_path(self.model_args)
-
-        patch_tied_tensors_bug(self.model_args.model)
-        modify_save_pretrained(self.model_args.model)
-
-        # Initialize processor
-        if isinstance(self.model_args.processor, (str, type(None))):
-            self.model_args.processor = initialize_processor_from_path(
-                self.model_args, self.model_args.model
-            )
-            # TODO: move to init once stage runner is removed
-            self.processor = self.model_args.processor
-
-        # Set minimum tokens per module if data arguments are provided
-        if self.dataset_args:
-            self.min_tokens_per_module = self.dataset_args.min_tokens_per_module
-
-    def check_tied_embeddings(self):
-        """
-        Logs a warning if the model has tied word embeddings.
-
-        The `tie_word_embeddings` flag may cause issues during saving in the one-shot
-        calibration workflow due to shared tensor addresses.
-        """
-        if self.model_args.tie_word_embeddings:
-            logger.debug(
-                "The tie_word_embeddings flag is by default set to False. "
-                "This guarantees that the one-shot algorithm saves the final "
-                "weights without errors. Detected tie_word_embeddings=True. "
-                "This may cause issues with the one-shot algorithm on save."
-            )
-
-    def _post_process(self):
-        """
-        Executes post-calibration steps.
-
-        This method saves the model and resets lifecycle actions if the `output_dir`
-        is not the default directory.
-
-        Raises:
-            ValueError: If saving fails due to invalid configurations.
-        """
-        if self.output_dir is not None:
-            self.save()
-            return
-
-        logger.warning(
-            "Optimized model not saved. To save, please provide",
-            "`output_dir` as input arg.",
-            "Ex. `oneshot(..., output_dir=...)`",
-        )
-
 
 def oneshot(**kwargs) -> PreTrainedModel:
     one_shot = Oneshot(**kwargs)