Only resize embeddings when necessary (#20043)

* Only resize embeddings when necessary

* Add comment

examples/pytorch/summarization/run_summarization.py

@@ -422,7 +422,11 @@ def main():
         use_auth_token=True if model_args.use_auth_token else None,
     )
 
-    model.resize_token_embeddings(len(tokenizer))
+    # We resize the embeddings only when necessary to avoid index errors. If you are creating a model from scratch
+    # on a small vocab and want a smaller embedding size, remove this test.
+    embedding_size = model.get_input_embeddings().weight.shape[0]
+    if len(tokenizer) > embedding_size:
+        model.resize_token_embeddings(len(tokenizer))
 
     if model.config.decoder_start_token_id is None and isinstance(tokenizer, (MBartTokenizer, MBartTokenizerFast)):
         if isinstance(tokenizer, MBartTokenizer):