[compile] Apply stored functorch config while finalizing loaded artifacts. (#36582)

Signed-off-by: zhxchen17 <zhxchen17@fb.com>

vllm/compilation/caching.py

@@ -369,8 +369,14 @@ class VllmSerializableFunction(SerializableCallable):  # type: ignore[misc]
 
         from vllm.compilation.backends import VllmBackend
 
+        saved_aot_autograd_config = self.aot_autograd_config
+        if saved_aot_autograd_config is not None:
+            functorch_ctx = torch._functorch.config.patch(saved_aot_autograd_config)
+        else:
+            functorch_ctx = contextlib.nullcontext()
+
         vllm_backend = VllmBackend(vllm_config, self.prefix, self.is_encoder)
-        with tracing(TracingContext(self._fake_mode)):
+        with tracing(TracingContext(self._fake_mode)), functorch_ctx:
             result = vllm_backend(self.graph_module, list(self.example_inputs))
             self.optimized_call = result.optimized_call
             self.vllm_backend = vllm_backend

vllm/compilation/piecewise_backend.py

@@ -258,22 +258,6 @@ class PiecewiseBackend:
             else:
                 args_list = get_fake_args_from_graph(self.graph)
 
-            # TODO(https://github.com/vllm-project/vllm/issues/35766)
-            # Can we remove strict_autograd_cache and
-            # force_non_lazy_backward_lowering overrides?
-            # I added them explicitly because this is what they are
-            # set to before the refactor
-            # (https://github.com/vllm-project/vllm/pull/35472).
-            # They affect the aotautograd cache key computation
-            # but they shouldn't have any effect on the actual
-            # compilation.
-            config_patches = dict(
-                bundled_autograd_cache=True,
-                strict_autograd_cache=False,
-            )
-            if hasattr(torch._functorch.config, "force_non_lazy_backward_lowering"):
-                config_patches["force_non_lazy_backward_lowering"] = False
-            with torch._functorch.config.patch(**config_patches):
             range_entry.runnable = self.vllm_backend.compiler_manager.compile(
                 self.graph,
                 args_list,