[Dynamo] Support tensor is not tensor (pytorch#118840)

Fixes Meta internal use case.

Pull Request resolved: pytorch#118840
Approved by: https://github.com/yf225

test/dynamo/test_functions.py

@@ -2105,6 +2105,21 @@ def fn(x, y):
         self.assertEqual(fn(x, y), fn_opt(x, y))
         self.assertEqual(fn(x, x), fn_opt(x, x))
 
+    def test_is_not_tensor_tensor(self):
+        def fn(x, y):
+            if x is not y:
+                return x * 2
+            else:
+                return x + y
+
+        fn_opt = torch.compile(backend="eager", fullgraph=True, dynamic=True)(fn)
+
+        x = torch.zeros(2)
+        y = torch.ones(2)
+
+        self.assertEqual(fn(x, y), fn_opt(x, y))
+        self.assertEqual(fn(x, x), fn_opt(x, x))
+
     def test_is_mutated_tensor_tensor(self):
         def fn(x):
             y = x.add_(1)

torch/_dynamo/variables/builtin.py

@@ -1615,13 +1615,17 @@ def _unimplemented():
         if isinstance(left, TensorVariable) or isinstance(right, TensorVariable):
             from .builder import wrap_fx_proxy_cls
 
-            if op is operator.is_:
-                return ConstantVariable.create(
+            if op in [operator.is_, operator.is_not]:
+                is_result = (
                     isinstance(left, TensorVariable)
                     and isinstance(right, TensorVariable)
                     and id(extract_fake_example_value(left.as_proxy().node))
                     == id(extract_fake_example_value(right.as_proxy().node))
                 )
+                if op is operator.is_:
+                    return ConstantVariable.create(is_result)
+                else:
+                    return ConstantVariable.create(not is_result)
 
             if op not in supported_tensor_comparison_ops.values():
                 _unimplemented()