Stop recursion on trivial replacement (#97903)
Pattern replacement behaves incorrectly when the replacement pattern maps inputs to outputs (such a pattern can be used to replace redundant code). However, current code in `torch.fx.subgraph_rewriter._replace_pattern` causes the list of replacement nodes to include the entire graph before that node, resulting in an exponential slowdown due to recursive calls traversing the entire graph multiple times.
The proposed fix is to add a check in `_replace_pattern` to prevent the call to `get_replacement_nodes`:
```python
for ret_node in copied_returning_nodes:
if ret_node in match.placeholder_nodes:
replacement_nodes.append(ret_node)
else:
get_replacement_nodes(ret_node)
```
Fixes #97817
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97903
Approved by: https://github.com/angelayi
