[dynamo][guards] Skip guards on constant func.__defaults__ elements (pytorch#159209)

Func.__defaults__ is a tuple. Therefore, we can skip guards on immutable elements. Mutable elements are still guarded.

Pull Request resolved: pytorch#159209
Approved by: https://github.com/jansel

Author: anijain2305

torch/_dynamo/config.py

@@ -354,6 +354,9 @@
 # the dictionary tag is same across invocation calls.
 skip_tensor_guards_with_matching_dict_tags = True
 
+# Skips guards on func.__defaults__ if the element to be guarded is a constant
+skip_guards_on_constant_func_defaults = True
+
 # If True, raises exception if TorchDynamo is called with a context manager
 raise_on_ctx_manager_usage = True
 

torch/_dynamo/variables/functions.py

@@ -161,7 +161,10 @@ def bind_args_cached(func, tx, fn_source, args, kwargs):
         elif name in spec.pos_default_map:
             idx = spec.pos_default_map[name]
             default_source = None
-            if fn_source:
+            if fn_source and not (
+                ConstantVariable.is_literal(spec.defaults[idx])
+                and config.skip_guards_on_constant_func_defaults
+            ):
                 default_source = DefaultsSource(fn_source, idx)
             ba[name] = wrap_bound_arg(tx, spec.defaults[idx], default_source)
         else: