[`GPTNeo`] Fix gradient checkpointing bug (#21733)

* fix bug

* forward contrib credits from discussions

* change logic

---------
Co-authored-by: edbeeching <edbeeching@users.noreply.github.com>

src/transformers/models/gpt_neo/modeling_gpt_neo.py

@@ -587,6 +587,13 @@ class GPTNeoModel(GPTNeoPreTrainedModel):
 
         output_shape = input_shape + (hidden_states.size(-1),)
 
+        if self.gradient_checkpointing and self.training:
+            if use_cache:
+                logger.warning(
+                    "`use_cache=True` is incompatible with gradient checkpointing. Setting `use_cache=False`..."
+                )
+                use_cache = False
+
         presents = () if use_cache else None
         all_self_attentions = () if output_attentions else None
         all_hidden_states = () if output_hidden_states else None
@@ -595,11 +602,6 @@ class GPTNeoModel(GPTNeoPreTrainedModel):
                 all_hidden_states = all_hidden_states + (hidden_states,)
 
             if self.gradient_checkpointing and self.training:
-                if use_cache:
-                    logger.warning(
-                        "`use_cache=True` is incompatible with gradient checkpointing. Setting `use_cache=False`..."
-                    )
-                    use_cache = False
 
                 def create_custom_forward(module):
                     def custom_forward(*inputs):