Refactor UnflattenedModule's adapt flat args (pytorch#140840)

Test Plan: unblocks model launch

Differential Revision: D66014709

Pull Request resolved: pytorch#140840
Approved by: https://github.com/pianpwk

torch/export/unflatten.py

@@ -519,6 +519,31 @@ def _print_graph(self):
             if hasattr(mod, "graph") and isinstance(mod.graph, torch.fx.Graph):
                 print(mod.graph)
 
+    def _adapt_flat_args(self, flat_args, in_spec):
+        signature = self.module_call_graph[0].signature
+        if in_spec == signature.in_spec:
+            return flat_args
+
+        if self.flat_args_adapter is None:
+            raise TypeError(
+                "There is no flat args adapter sepcified. "
+                "Are you sure you are calling this with the right arguments? "
+            )
+        else:
+            flat_args = self.flat_args_adapter.adapt(
+                target_spec=signature.in_spec,
+                input_spec=in_spec,
+                input_args=flat_args,
+            )
+
+            if len(flat_args) != signature.in_spec.num_leaves:
+                raise TypeError(
+                    f"Flat args adaption failed, number of args mismatch "
+                    f"Adatped: {len(flat_args)} \n"
+                    f"Exported module: {signature.in_spec.num_leaves}"
+                )
+            return flat_args
+
     def forward(self, *args, **kwargs):
         signature = self.module_call_graph[0].signature
 
@@ -544,26 +569,9 @@ def forward(self, *args, **kwargs):
                     f"Input treespec: {in_spec}. ",
                     f"Exported module treespec: {signature.in_spec}",
                 )
-            if self.flat_args_adapter is None:
-                raise TypeError(
-                    "There is no flat args adapter sepcified. "
-                    "Are you sure you are calling this with the right arguments? "
-                )
-            else:
-                if not self.adapted:
-                    print("Adapting flat arg to match exported module's treespec")
-                flat_args = self.flat_args_adapter.adapt(
-                    target_spec=signature.in_spec,
-                    input_spec=in_spec,
-                    input_args=flat_args,
-                )
-                self.adapted = True
-                if len(flat_args) != signature.in_spec.num_leaves:
-                    raise TypeError(
-                        f"Flat args adaption failed, number of args mismatch "
-                        f"Adatped: {len(flat_args)} \n"
-                        f"Exported module: {signature.in_spec.num_leaves}"
-                    )
+                print("Adapting flat arg to match exported module's treespec")
+            flat_args = self._adapt_flat_args(flat_args, in_spec)
+            self.adapted = True
 
         if self.check_input_constraints:
             # Import here to avoid an unfortunate circular dependency.