[dynamo][exceptions] Use exception subclass whenever possible (#134610)

Pull Request resolved: https://github.com/pytorch/pytorch/pull/134610
Approved by: https://github.com/drisspg, https://github.com/jansel

test/dynamo/test_exceptions.py

@@ -267,6 +267,29 @@ class ExceptionTests(torch._dynamo.test_case.TestCase):
         x = torch.ones(4)
         self.assertEqual(mod(x), opt_mod(x))
 
+    def test_attribute_error_from_getattr(self):
+        class Mock:
+            def __init__(self):
+                self.a = 5
+
+            def __getattr__(self, name):
+                if name != "a":
+                    raise AttributeError("missing")
+                return self.__dict__["a"]
+
+        mock = Mock()
+
+        def fn(x):
+            if hasattr(mock, "b"):
+                return torch.cos(x)
+            return torch.sin(x)
+
+        opt_fn = torch.compile(fn, backend="eager", fullgraph=True)
+        x = torch.randn(4)
+        ref = fn(x)
+        res = opt_fn(x)
+        self.assertEqual(ref, res)
+
     def test_stop_iteration(self):
         def zip_longest(*iterables, fillvalue=None):
             # Get the iterators for each iterable

torch/_dynamo/symbolic_convert.py

@@ -1379,9 +1379,10 @@ class InstructionTranslatorBase(
 
             # 2) when user raises exception instance
             if isinstance(val, variables.ExceptionVariable):
-                if val.exc_type is StopIteration:
+                if observed_exception_type := exc.observed_exception_map.get(
-                    # StopIteration is used to find the end of iteration while tracing __next__
+                    val.exc_type
-                    raise exc.ObservedUserStopIteration(f"raised exception {val}")
+                ):
+                    raise observed_exception_type(f"raised exception {val}")
                 raise exc.ObservedException(f"raised exception {val}")
             unimplemented(f"raise {exc}")
         else: