move and fix logic to update unbacked bindings (#146115)

Summary:
Previously we were touching up unbacked bindings between Dynamo and AOTAutograd in strict export, but the logic had a bug: if an unbacked symint gets substituted by a backed symint, we would put the backed symint in the unbacked bindings (the check `is_symbol` was not enough here).

This PR fixes this logic, and moreover, moves it into the serializer instead, because we don't need this adjustment outside serde.

Test Plan: added test

 D68880766

Pull Request resolved: https://github.com/pytorch/pytorch/pull/146115
Approved by: https://github.com/pianpwk

test/export/test_export.py

@@ -980,6 +980,44 @@ graph():
         ep_output = ep.module()(seq_embeddings, mask, exp)
         self.assertTrue(torch.allclose(output, ep_output))
 
+    def test_mask_torch_check(self):
+        class TestModule(torch.nn.Module):
+            def forward(self, seq_embeddings, mask, exp):
+                output = seq_embeddings[mask]
+                # output.shape has unbacked symint, assert side knowledge of
+                # output.shape as exp.shape to force it to have backed symint
+                torch._check(output.size(0) == exp.size(0))
+                final_output = output * 2
+                return final_output
+
+        m = TestModule()
+
+        seq_embeddings = torch.randn(5, 5)
+        mask = torch.ones(5, 5, dtype=torch.bool)
+        exp = torch.randn(25)
+        output = m(seq_embeddings, mask, exp)
+
+        batch = torch.export.Dim("batch")
+        exp_size = torch.export.Dim("exp_size", max=100)
+        ep = export(
+            m,
+            (seq_embeddings, mask, exp),
+            dynamic_shapes={
+                "seq_embeddings": (batch, None),
+                "mask": (batch, None),
+                "exp": (exp_size,),
+            },
+        )
+        ep_output = ep.module()(seq_embeddings, mask, exp)
+        self.assertTrue(torch.allclose(output, ep_output))
+
+        seq_embeddings = torch.randn(6, 5)
+        mask = torch.ones(6, 5, dtype=torch.bool)
+        exp = torch.randn(30)
+        output = m(seq_embeddings, mask, exp)
+        ep_output = ep.module()(seq_embeddings, mask, exp)
+        self.assertTrue(torch.allclose(output, ep_output))
+
     def test_setgrad_lifted_tensor(self):
         class M(torch.nn.Module):
             def forward(self, x, y):
@@ -9691,7 +9729,6 @@ def forward(self, p_bar_linear_weight, p_bar_linear_bias, x):
             "torch.ops.profiler._record_function_enter_new.default", 0, exactly=True
         ).run(ep.graph_module.code)
 
-    @testing.expectedFailureSerDerNonStrict
     def test_replace_unbacked_with_very_large_upperbound(self):
         # beyond 2^53 where python floats lose precision
         VERY_LARGE_INT = 1000000007999999992

torch/_export/serde/serialize.py

@@ -635,9 +635,19 @@ class GraphModuleSerializer(metaclass=Final):
         if unbacked_bindings := node.meta.get("unbacked_bindings"):
             # serialize the symbol names of unbacked bindings;
             # reconstruct the key paths to those symbols when deserializing
-            ret["unbacked_bindings"] = ",".join(
-                u.name for u in unbacked_bindings.keys()
-            )
+            val = node.meta["val"]
+            new_unbacked_bindings = {}
+            for key in unbacked_bindings.values():
+                expr = pytree.key_get(val, key).node.expr
+                if expr.is_symbol and (
+                    expr.name.startswith(prefix_str[SymT.UNBACKED_FLOAT])
+                    or expr.name.startswith(prefix_str[SymT.UNBACKED_INT])
+                ):
+                    new_unbacked_bindings[expr] = key
+            if new_unbacked_bindings:
+                ret["unbacked_bindings"] = ",".join(
+                    u.name for u in new_unbacked_bindings.keys()
+                )
 
         if stack_trace := node.meta.get("stack_trace"):
             ret["stack_trace"] = stack_trace

torch/export/_trace.py

@@ -1399,22 +1399,6 @@ def _strict_export_lower_to_aten_ir(
     export_graph_signature = aten_export_artifact.sig
     constants = aten_export_artifact.constants
 
-    # update unbacked bindings that might have gone out of sync
-    # between Dynamo and AOTAutograd
-    for node in gm.graph.nodes:
-        if "unbacked_bindings" in node.meta:
-            old_unbacked_bindings = node.meta["unbacked_bindings"]
-            val = node.meta["val"]
-            new_unbacked_bindings = {}
-            for key in old_unbacked_bindings.values():
-                expr = pytree.key_get(val, key).node.expr
-                if expr.is_symbol:
-                    new_unbacked_bindings[expr] = key
-            if new_unbacked_bindings:
-                node.meta["unbacked_bindings"] = new_unbacked_bindings
-            else:
-                del node.meta["unbacked_bindings"]
-
     _populate_param_buffer_metadata_to_new_gm(
         params_buffers_to_node_meta, gm, export_graph_signature
     )