[inductor] Add unbacked symints binding in ShapeProp (#144605)

Summary: ShapeProp  doesn't know how to propagate unbacked. Patch it up to propagate unbacked symints like PropagateUnbackedSymInts.

Test Plan:
```
buck run mode/dev-nosan  fbcode//caffe2/test:fx -- -r test_shape_prop_unbacked_sym
```

Differential Revision: D68050073

Pull Request resolved: https://github.com/pytorch/pytorch/pull/144605
Approved by: https://github.com/guowentian, https://github.com/pianpwk

test/test_fx.py

@@ -1793,6 +1793,25 @@ class TestFX(JitTestCase):
             if node.op in {'placeholder'}:
                 self.assertEqual(node.meta['tensor_meta'].memory_format, torch.channels_last_3d)
 
+    def test_shape_prop_unbacked_sym(self):
+        from torch._dynamo.utils import detect_fake_mode
+
+        class M(torch.nn.Module):
+            def forward(self, x: torch.Tensor):
+                return torch.nonzero(x)
+
+        inp = (torch.tensor([1, 0, 1, 0]),)
+        gm = torch.export.export(M(), inp).module()
+        fake_inputs = [
+            node.meta.get("val")
+            for node in gm.graph.nodes
+            if node.op == "placeholder"
+        ]
+        inp = fake_inputs
+        fake_mode = detect_fake_mode(inp)
+        shape_prop.ShapeProp(gm=gm, fake_mode=fake_mode).propagate(*inp)
+        self.assertEqual(len(fake_mode.shape_env.pending_fresh_unbacked_symbols), 0)
+
     def test_nn_module_stack(self):
         class SubModule(torch.nn.Module):
             def __init__(self) -> None:

torch/fx/passes/shape_prop.py

@@ -154,6 +154,11 @@ class ShapeProp(torch.fx.Interpreter):
         self.real_module = self.module
 
     def run_node(self, n: Node) -> Any:
+        from torch.fx.experimental.symbolic_shapes import (
+            compute_unbacked_bindings,
+            rebind_unbacked,
+        )
+
         try:
             if self.fake_module is not None:
                 # Hacky swap. Alternatively, we could do this with overriding
@@ -163,6 +168,7 @@ class ShapeProp(torch.fx.Interpreter):
                 if self.fake_mode is not None:
                     with self.fake_mode, enable_python_dispatcher():
                         result = super().run_node(n)
+                        rebind_unbacked(self.fake_mode.shape_env, n, result)
                 else:
                     result = super().run_node(n)
             finally:
@@ -187,6 +193,12 @@ class ShapeProp(torch.fx.Interpreter):
         if found_tensor:
             n.meta["tensor_meta"] = meta
 
+        if self.fake_mode:
+            if (shape_env := self.fake_mode.shape_env) and (
+                symbol_to_path := compute_unbacked_bindings(shape_env, result)
+            ):
+                n.meta["unbacked_bindings"] = symbol_to_path
+
         n.meta["type"] = type(result)
         return result