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

This reverts commit c1ad4b8e7a16f54c35a3908b56ed7d9f95eef586.

Reverted https://github.com/pytorch/pytorch/pull/156623 on behalf of https://github.com/albanD due to Breaks Dynamo tests in trunk ([comment](https://github.com/pytorch/pytorch/pull/156623#issuecomment-3001806841))

test/dynamo/test_repros.py

@@ -4460,20 +4460,6 @@ class ReproTests(torch._dynamo.test_case.TestCase):
         # frame_count should stay at 1.
         self.assertEqual(cnt.frame_count, 1)
 
-    def test_tensor_set_data_mismatched_dtype(self):
-        def func(x, y):
-            x.data = y.to(dtype=torch.bfloat16)
-
-        x1 = torch.tensor([], dtype=torch.float32)
-        x2 = torch.tensor([], dtype=torch.float32)
-        y1 = torch.tensor([1, 2, 3], dtype=torch.float32)
-        y2 = torch.tensor([1, 2, 3], dtype=torch.float32)
-        func(x1, y1)
-        torch.compile(func, backend="eager")(x2, y2)
-        self.assertEqual(x1, x2)
-        self.assertEqual(x1.data, x2.data)
-        self.assertEqual(y1, y2)
-
     def test_user_ctor_ctx_manager(self):
         class UserCtxManager:
             def __enter__(self):

torch/_dynamo/variables/builtin.py

@@ -2175,17 +2175,6 @@ 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",
-                            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