[compiler] Switch to the new dynamo export API.

Summary:
Replacing the API usage while removing some dead code.

Test Plan:
```
NGPU=4 CONFIG_FILE=./torchtitan/models/deepseek_v3/train_configs/debug_model.toml ./run_train.sh --model.name compiler_toolkit.deepseek_v3 --parallelism.data_parallel_shard_degree=2 --parallelism.tensor_parallel_degree=2 --parallelism.expert_parallel_degree=2 --activation_checkpoint.mode none

NGPU=4 CONFIG_FILE=./torchtitan/models/deepseek_v3/train_configs/debug_model.toml ./run_train.sh --model.name compiler_toolkit.deepseek_v3 --parallelism.data_parallel_shard_degree=2 --parallelism.tensor_parallel_degree=2 --parallelism.expert_parallel_degree=2 --activation_checkpoint.mode none --model.flavor=debugmodel_flex_attn

NGPU=8 CONFIG_FILE=./torchtitan/models/llama3/train_configs/debug_model.toml ./run_train.sh --model.name compiler_toolkit.llama3 --parallelism.data_parallel_shard_degree=2 --parallelism.tensor_parallel_degree=4

NGPU=8 CONFIG_FILE=./torchtitan/models/llama3/train_configs/debug_model.toml ./run_train.sh --model.name compiler_toolkit.llama3 --parallelism.data_parallel_shard_degree=2 --parallelism.tensor_parallel_degree=4 --model.flavor=debugmodel_flex_attn
```

Author: zhxchen17

torchtitan/experiments/compiler_toolkit/graph_utils.py

@@ -8,7 +8,7 @@
 from typing import Callable, Optional
 
 import torch
-from torch._dynamo.functional_export import _dynamo_graph_capture_for_export
+from torch._dynamo.functional_export import dynamo_graph_capture_for_export
 from torch._functorch.aot_autograd import (
     aot_compile_joint_with_descriptors,
     aot_export_joint_with_descriptors,
@@ -33,88 +33,19 @@ def _clear_traced_params_buffers(
         setattr(traced_module, key, buffer)
 
 
-def _restore_state_dict(
-    original_module: torch.nn.Module, traced_module: torch.fx.GraphModule
-) -> None:
-    """
-    TODO: move this into torch.export
-    Restores the state dict of the traced module to match the original module exactly.
-    Preserves the original FQNs with dots, creating intermediate empty modules as needed.
-    Ensures that the ordering of parameters/buffers matches the original module.
-    """
-    # Build ID-based lookups for traced module params/buffers
-    traced_params: dict[int, tuple[str, torch.nn.Parameter]] = {}
-    for name, param in traced_module.named_parameters(remove_duplicate=False):
-        traced_params[id(param)] = (name, param)
-
-    traced_buffers: dict[int, tuple[str, torch.Tensor]] = {}
-    for name, buffer in traced_module.named_buffers(remove_duplicate=False):
-        traced_buffers[id(buffer)] = (name, buffer)
-
-    # Build mapping from old names to new names for graph node updates
-    name_mapping: dict[str, str] = {}
-
-    # Restore parameters in the order they appear in original module
-    for orig_name, orig_param in original_module.named_parameters(
-        remove_duplicate=False
-    ):
-        if id(orig_param) in traced_params:
-            # This param exists in traced module - restore it with original FQN
-            traced_name, traced_param = traced_params[id(orig_param)]
-            torch.fx.graph_module._assign_attr(traced_param, traced_module, orig_name)
-            torch.fx.graph_module._del_attr(traced_module, traced_name)
-            name_mapping[traced_name] = orig_name
-        else:
-            # This param doesn't exist in traced module - add it
-            torch.fx.graph_module._assign_attr(orig_param, traced_module, orig_name)
-
-    # Restore buffers in the order they appear in original module
-    for orig_name, orig_buffer in original_module.named_buffers(remove_duplicate=False):
-        if id(orig_buffer) in traced_buffers:
-            # This buffer exists in traced module - restore it with original FQN
-            traced_name, traced_buffer = traced_buffers[id(orig_buffer)]
-            torch.fx.graph_module._assign_attr(orig_buffer, traced_module, orig_name)
-            name_mapping[traced_name] = orig_name
-            torch.fx.graph_module._del_attr(traced_module, traced_name)
-        else:
-            # This buffer doesn't exist in traced module - add it
-            torch.fx.graph_module._assign_attr(orig_buffer, traced_module, orig_name)
-
-    param_names = [v[0] for v in traced_params.values()]
-    buffer_names = [v[0] for v in traced_buffers.values()]
-    const_keys = set(param_names + buffer_names).difference(set(name_mapping.keys()))
-
-    _clear_traced_params_buffers(traced_module, const_keys)
-
-    # Update get_attr nodes in the graph to use the correct FQNs
-    for node in traced_module.graph.nodes:
-        if node.op == "get_attr" and node.target in name_mapping:
-            node.target = name_mapping[node.target]
-
-    traced_module.recompile()
-
-
 def export_joint(
     model, args, kwargs=None
 ) -> tuple[JointWithDescriptors, TracingContext]:
     if kwargs is None:
         kwargs = {}
     assert isinstance(args, tuple)
     assert isinstance(kwargs, dict)
-    with torch._dynamo.config.patch(
-        install_free_tensors=True
-    ), torch.fx.traceback.preserve_node_meta():
-        # TODO: switch to use the official graph_capture API once it is ready
-        gm = _dynamo_graph_capture_for_export(model)(*args, **kwargs)
-
-        # Restore the state dict to match the original module
-        _restore_state_dict(model, gm)
-
+    with torch.fx.traceback.preserve_node_meta():
+        gm = dynamo_graph_capture_for_export(model)(*args, **kwargs)
         logger.info("Dynamo gm:")
         logger.info(gm.print_readable(print_output=False))
 
-        fake_mode = gm.meta.get("fake_mode", None)
-        tracing_context = TracingContext(fake_mode)
+        tracing_context = gm.meta["tracing_context"]
 
     with tracing(tracing_context):
         return (