[dynamo] Graph break on torch.Tensor.data assignment with mismatched dtype (#156623)

Fixes #152162. Discussed with @bdhirsh and decided this is the easiest
workaround for now.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/156623
Approved by: https://github.com/bdhirsh

torch/_dynamo/variables/builtin.py

@@ -2175,6 +2175,17 @@ class BuiltinVariable(VariableTracker):
                                 "the mutation out of `torch.compile` region",
                             ],
                         )
+                    elif obj.dtype != val.dtype:  # type: ignore[attr-defined]
+                        unimplemented_v2(
+                            gb_type="Failed to mutate tensor data attribute to different dtype",
+                            context=f"setattr({obj}, {name}, {val})",
+                            explanation="Dyanmo only supports mutating `.data`"
+                            " of tensor to a new one with the same dtype",
+                            hints=[
+                                "Don't mutate `.data` on this tensor, or move "
+                                "the mutation out of `torch.compile` region",
+                            ],
+                        )
 
                     # Remove the old reference in tracked fakes - if we don't do this
                     # new .data value size and shape differences will cause