[Dynamo] Guard serialization for SEQUENCE_LENGTH (#152730)

Tests only; no other changes needed. Test logic uses a tuple function input to trigger installation of a SEQUENCE_LENGTH guard.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/152730
Approved by: https://github.com/jansel
ghstack dependencies: #152725, #152727, #152728

test/dynamo/test_guard_serialization.py

@@ -655,6 +655,39 @@ class TestGuardSerialization(torch._inductor.test_case.TestCase):
         ):
             self._test_serialization("CLOSURE_MATCH", fn, x)
 
+    def test_sequence_length(self):
+        # tuple input installs a SEQUENCE_LENGTH guard
+        def fn(t, x):
+            return t[1] + x
+
+        t = tuple(torch.randn(3) for _ in range(3))
+        x = torch.randn(3)
+
+        ref, loaded = self._test_serialization("SEQUENCE_LENGTH", fn, t, x)
+        self._test_check_fn(ref, loaded, {"x": x, "t": t}, True)
+        self._test_check_fn(
+            ref,
+            loaded,
+            {
+                "x": torch.randn(3),
+                "t": tuple(torch.randn(3) for _ in range(3)),
+            },
+            True,
+        )
+        # different types in tuple of same length shouldn't fail SEQUENCE_LENGTH guard
+        # (it should fail the separate TYPE_MATCH guard but that isn't tested here)
+        self._test_check_fn(ref, loaded, {"x": torch.randn(3), "t": (0, 1, 2)}, True)
+        # different length tuple
+        self._test_check_fn(
+            ref,
+            loaded,
+            {
+                "x": torch.randn(3),
+                "t": tuple(torch.randn(3) for _ in range(4)),
+            },
+            False,
+        )
+
     def test_dict_version(self):
         def fn(x):
             return pytree.tree_leaves(x)[0] + 1