Fix fake mode detection

Differential Revision: D87577206

Author: angelayi

exir/program/_program.py

@@ -97,6 +97,7 @@
 from torch.fx._compatibility import compatibility
 from torch.fx.passes.infra.pass_manager import PassManager
 from torch.utils import _pytree as pytree
+from torch._export.utils import _detect_fake_mode_from_gm
 
 Val = Any
 
@@ -333,7 +334,8 @@ def lift_constant_tensor_pass(ep):
     graph_signature = ep.graph_signature
     buffers = list(graph_signature.buffers)
 
-    fake_mode = list(ep.graph.nodes)[0].meta["val"].fake_mode
+    fake_mode = _detect_fake_mode_from_gm(ep.graph_module)
+
     first_user_input = None
     lifted_constants = []
     for node in ep.graph.nodes: