Dynamic Inputs for fx traced GPTNeoLM 
# 🚀 Feature request

I've been looking a little into using torch.fx + HF lately, and run into a problem that the traced GPTNeoLM can't take dynamic inputs - would love to know what work would be needed to enable that, and what the current blockers are - it would be great to be able to use the traced module for inference.

I'm assuming the problem has something to do with caching of keys/values?

## Your contribution

Given guidance, I could put some work into adding this feature, yes :) 
cc @michaelbenayoun <|||||>Hi @sdtblck ,
The issue with dynamic inputs is not related to the `past_key_values` but to dynamic control-flow in the model forward pass implementation. The PR #14321, that I plan to merge at some point (hopefully before the end of the year) solves this kind of issues for the supported models.<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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