guard generalized scatter import (#4066)

Author: apbose

py/torch_tensorrt/dynamo/lowering/passes/_FakeTensorUpdater.py

@@ -17,6 +17,12 @@
 )
 from torch.utils._ordered_set import OrderedSet
 
+# _generalized_scatter may not exist in all PyTorch versions
+try:
+    from torch._inductor.fx_passes.reinplace import _generalized_scatter
+except (ImportError, AttributeError):
+    _generalized_scatter = None
+
 
 # Adapted from torch._inductor.fx_utils.FakeTensorUpdater
 class FakeTensorUpdater:
@@ -159,8 +165,10 @@ def should_process_node(node: torch.fx.Node) -> bool:
             return node.op == "call_function" and (
                 isinstance(node.target, torch._ops.OpOverload)
                 or node.target is operator.getitem
-                or node.target
-                is torch._inductor.fx_passes.reinplace._generalized_scatter
+                or (
+                    _generalized_scatter is not None
+                    and node.target is _generalized_scatter
+                )
             )
 
         to_process = OrderedSet[int]()