[dynamo] Fix aliasing issue for dict.copy that escapes the graph (pytorch#141715)

Dynamo accidentally passed the original `ConstDictVariable.source` to
the result of `dict.copy(...)`, which caused aliasing issue when the
result escapes the graph (e.g., is a return value).

This patch fixes that and adds a regression test.

Pull Request resolved: pytorch#141715
Approved by: https://github.com/jansel
ghstack dependencies: pytorch#141713, pytorch#141714

Author: StrongerXi

test/dynamo/test_misc.py

@@ -2833,6 +2833,19 @@ def fn(d):
         self.assertEqual(cnts.frame_count, 1)
         self.assertEqual(cnts.op_count, 1)
 
+    def test_dict_copy_alias(self):
+        @torch.compile(backend="eager", fullgraph=True)
+        def run(x, d0):
+            d1 = d0.copy()
+            d1[0] = 1
+            return x + 1, d1
+
+        d0 = {}
+        res, d1 = run(torch.zeros(1), d0)
+        self.assertTrue(same(res, torch.ones(1)))
+        self.assertEqual(d0, {})
+        self.assertEqual(d1, {0: 1})
+
     def test_dict_subclass_get_method(self):
         class dotdict(dict):
             """dot.notation access to dictionary attributes"""

torch/_dynamo/variables/dicts.py

@@ -312,7 +312,9 @@ def call_method(
             return DictValues(self)
         elif name == "copy":
             assert not (args or kwargs)
-            return self.clone(items=self.items.copy(), mutation_type=ValueMutationNew())
+            return self.clone(
+                items=self.items.copy(), mutation_type=ValueMutationNew(), source=None
+            )
         elif name == "__len__":
             assert not (args or kwargs)
             return ConstantVariable.create(len(self.items))