Speedup model init on CPU (by 10x+ for llama-3-8B as one example) (#31771)

* 1,100%!

* Clean

* Don't touch DS

* Experiment with dtype allocation

* skip test_load_save_without_tied_weights test

* A little faster

* Include proper upscaling?

* Fixup tests

* Potentially skip?

* Let's see if this fixes git history

* Maintain new dtype

* Fin

* Rm hook idea for now

* New approach, see what breaks

* stage

* Clean

* Stash

* Should be fin now, just need to mark failing models

* Clean up

* Simplify

* Deal with weird models

* Enc/Dec

* Skip w/ reason

* Adjust test

* Fix test

* one more test

* Keep experimenting

* Fix ref

* TO REMOVE: testing feedback CI

* Right push

* Update tests/utils/test_modeling_utils.py

Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* disable

* Add new func

* Test nits from Amy

* Update src/transformers/modeling_utils.py

Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

* Adjust comment

* Adjust comment on skip

* make private

* Fin

* Should be a not flag

* Clarify and rename test

---------

Co-authored-by: Marc Sun <marc@huggingface.co>
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>
Co-authored-by: amyeroberts <22614925+amyeroberts@users.noreply.github.com>

tests/models/switch_transformers/test_modeling_switch_transformers.py

@@ -720,6 +720,12 @@ class SwitchTransformersModelTest(ModelTesterMixin, GenerationTesterMixin, Pipel
             attn_weights = out[attn_name] if attn_name == attention_names[0] else out[attn_name][-1]
             self.assertEqual(sum([w.sum().item() for w in attn_weights]), 0.0)
 
+    @unittest.skip(
+        reason="This architecure has tied weights by default and there is no way to remove it, check: https://github.com/huggingface/transformers/pull/31771#issuecomment-2210915245"
+    )
+    def test_load_save_without_tied_weights(self):
+        pass
+
 
 class SwitchTransformersEncoderOnlyModelTester:
     def __init__(
@@ -843,6 +849,12 @@ class SwitchTransformersEncoderOnlyModelTest(ModelTesterMixin, unittest.TestCase
         config_and_inputs = self.model_tester.prepare_config_and_inputs()
         self.model_tester.create_and_check_model_fp16_forward(*config_and_inputs)
 
+    @unittest.skip(
+        reason="This architecure has tied weights by default and there is no way to remove it, check: https://github.com/huggingface/transformers/pull/31771#issuecomment-2210915245"
+    )
+    def test_load_save_without_tied_weights(self):
+        pass
+
 
 def use_task_specific_params(model, task):
     model.config.update(model.config.task_specific_params[task])