[dynamo] Support is comparison for symnodes (pytorch#140754)

Fixes pytorch#109504.

Pull Request resolved: pytorch#140754
Approved by: https://github.com/williamwen42

Author: StrongerXi

test/dynamo/test_repros.py

@@ -6338,6 +6338,30 @@ def forward(self, x):
         res = opt_mod(x)
         self.assertEqual(ref, res)
 
+    def test_symnode_is_op(self):
+        @torch.compile(backend="eager", fullgraph=True, dynamic=True)
+        def f(x, xs):
+            if x.size(0) is xs:
+                return x + 1
+            else:
+                return x * 2
+
+        t = torch.randn(2)
+        res = f(t, [1, 2])
+        self.assertEqual(t * 2, res)
+
+    def test_symnode_is_not_op(self):
+        @torch.compile(backend="eager", fullgraph=True, dynamic=True)
+        def f(x, xs):
+            if x.size(0) is not xs:
+                return x + 1
+            else:
+                return x * 2
+
+        t = torch.randn(2)
+        res = f(t, [1, 2])
+        self.assertEqual(t + 1, res)
+
 
 instantiate_parametrized_tests(ReproTests)
 

torch/_dynamo/variables/tensor.py

@@ -69,6 +69,8 @@
     "<=": operator.le,
     "==": operator.eq,
     "!=": operator.ne,
+    "is": operator.is_,
+    "is not": operator.is_not,
 }
 # Ops that allow tensor <op> None
 supported_const_comparison_ops = {