Add is_ support for Tensors, force get_fake_value to reuse prev…

…iously computed `example_value` if available (#111565)

Summary:
Use FakeTensor id match as equivalent to object identity match

cc

X-link: pytorch/pytorch#111565
Approved by: https://github.com/ezyang

Reviewed By: izaitsevfb

Differential Revision: D50543481

fbshipit-source-id: 1ad6dbe37b481a070ed19c450db260b8ce033f14

userbenchmark/dynamo/dynamobench/_dynamo/utils.py

@@ -1337,6 +1337,15 @@ def get_debug_dir():
     return _get_debug_dir(debug_root)
 
 
+def extract_fake_example_value(node, required=True):
+    if "example_value" in node.meta and is_fake(node.meta["example_value"]):
+        return node.meta["example_value"]
+    elif required:
+        unimplemented("`FakeTensor` example value was required but not available")
+    else:
+        return None
+
+
 def get_fake_value(node, tx):
     """
     Run the computation represented by `node` using fake tensors and return the result.
@@ -1351,6 +1360,10 @@ def get_fake_value(node, tx):
 
     op = node.op
 
+    # FX Node should always return the same value
+    if "example_value" in node.meta and is_fake(node.meta["example_value"]):
+        return node.meta["example_value"]
+
     def fake_wrapper(e):
         if isinstance(e, torch.Tensor):
             assert is_fake(e)