The match for backward nodes might be in a different submod, so we should check all submod for potential matches.
In flex attention, this could happen if `mask_mod` has operations (such as index) that increase the seq_nr of the forward graph nodes. Then the backward flex_attention nodes cannot find a match in its own subgraph.
```
python test/functorch/test_aot_joint_with_descriptors.py -k preserve_annotate
```
Also tested on torchtitan joint_graph_runner branch. The flex_attention backward nodes are annotated now.
```
NGPU=8 CONFIG_FILE="./torchtitan/models/llama3/train_configs/debug_model.toml" LOG_RANK=0 TRAIN_FILE="torchtitan.train" TORCHFT_LIGHTHOUSE="http://localhost:29510" PYTORCH_ALLOC_CONF="expandable_segments:True" torchrun --nproc_per_node=8 --rdzv_backend c10d --rdzv_endpoint="localhost:0" --local-ranks-filter 0 --role rank --tee 3 -m torchtitan.train --job.config_file ./torchtitan/models/llama3/train_configs/debug_model.toml --model.name joint_graph_runner.llama3 --compile.enable --parallelism.data_parallel_shard_degree=2 --parallelism.tensor_parallel_degree=4 --model.flavor=debugmodel_flex_attn
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/165202
Approved by: https://github.com/SherlockNoMad
Builds on top of https://github.com/pytorch/pytorch/pull/163673 and https://github.com/pytorch/pytorch/pull/164174. This will be used in the followup PRs to apply regional inductor compilation.
The existing implementation let Dynamo trace into the `torch.fx.traceback.annotate`, but thats not what we want. We want Dynamo to essentially run the torch.fx.traceback.annotate function in eager, so that every Fx node created in Dynamo Fx graph has the custom meta node.
What does not work?
* We still have to set the context manager `torch.fx.traceback.preserve_node_meta()` in the user code because CI was unhappy. This can be fixed but with some perseverance.
* This does not work with graph breaks yet. But we can solve that problem, if needed, in a separate PR.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/164678
Approved by: https://github.com/SherlockNoMad, https://github.com/jansel, https://github.com/xmfan
