fix regression which creates a new fake tensor (#111864)

Fixes regression identified here: https://github.com/pytorch/pytorch/pull/111565/files/ccd6b373b5fba81b6141a6b93b2ffb6595dd49ae#r1369334484

Now that `get_fake_value` will identify aliases, we should not try to wrap the fake value again.

Pull Request resolved: #111864
Approved by: https://github.com/eellison

test/dynamo/test_modules.py

@@ -2221,18 +2221,18 @@ def foo(mod, x):
 
         mod = Mod()
         foo(mod, torch.rand([4]))
-        self.assertEqual(compiles_without_buffers, 1)
+        self.assertEqual(compiles_without_buffers, 0)
 
         foo(mod, torch.rand([4], dtype=torch.half))
-        self.assertEqual(compiles_without_buffers, 2)
+        self.assertEqual(compiles_without_buffers, 1)
 
         class Mod2(Mod):
             def __setattr__(self, name, value):
                 return super().__setattr__(name, value)
 
         foo(Mod2(), torch.rand([4]))
         # causes two compilations, bc unimplemented custom setattr
-        self.assertTrue(compiles_without_buffers >= 4)
+        self.assertTrue(compiles_without_buffers >= 2)
 
     def test_unspec_non_inlinable_module(self):
         mod = UnspecNonInlinableModule()

torch/_dynamo/utils.py

@@ -1360,7 +1360,7 @@ def get_fake_value(node, tx):
 
     op = node.op
 
-    # FX Node should always return the same value
+    # FX Node should always return the same fake value
     if "example_value" in node.meta and is_fake(node.meta["example_value"]):
         return node.meta["example_value"]
 

torch/_dynamo/variables/builtin.py

@@ -1238,13 +1238,8 @@ def call_setattr(
                     getattr_var = None
 
                 if isinstance(getattr_var, variables.TensorVariable):
-                    # get_fake_val will return a real tensor here because it's an attribute on the module (get_attr node)
-                    existing_attr = get_fake_value(getattr_var.as_proxy().node, tx)
-                    existing_fake_attr = (
-                        variables.builder.wrap_to_fake_tensor_and_record(
-                            existing_attr, tx, source=getattr_var.source, is_tensor=True
-                        )
-                    )
+                    # get_fake_val will get the same fake tensor
+                    existing_fake_attr = get_fake_value(getattr_var.as_proxy().node, tx)
 
                     # same tensor identiy, setattr is a no-op
                     mod_setattr = inspect.getattr_static(obj.module_type, "__setattr__")