optimizer __call__ to make dygraph faster (#37713)

* optimizer __call__ to make dygraph faster

* fix return type

python/paddle/fluid/dygraph/layers.py

@@ -881,12 +881,7 @@ class Layer(core.Layer):
     def _build_once(self, *args, **kwargs):
         pass
 
-    def __call__(self, *inputs, **kwargs):
-        # NOTE(Aurelius84): Why we still need param_guard here?
-        # In case of ControlFlow, true_fn and false_fn will contain
-        # parameters that may not trigger logic of `Operator` to create
-        # them. we add this to make sure all parameters is available.
-        with param_guard(self._parameters), param_guard(self._buffers):
+    def _dygraph_call_func(self, *inputs, **kwargs):
         for forward_pre_hook in self._forward_pre_hooks.values():
             hook_result = forward_pre_hook(self, inputs)
             if hook_result is not None:
@@ -917,6 +912,19 @@ class Layer(core.Layer):
 
         return outputs
 
+    def __call__(self, *inputs, **kwargs):
+        # NOTE(Aurelius84): Why we still need param_guard here?
+        # In case of ControlFlow, true_fn and false_fn will contain
+        # parameters that may not trigger logic of `Operator` to create
+        # them. we add this to make sure all parameters is available.
+        from paddle.fluid.dygraph.dygraph_to_static.program_translator import in_declarative_mode
+
+        if in_declarative_mode() and not framework.in_dygraph_mode():
+            with param_guard(self._parameters), param_guard(self._buffers):
+                return self._dygraph_call_func(*inputs, **kwargs)
+        else:
+            return self._dygraph_call_func(*inputs, **kwargs)
+
     def forward(self, *inputs, **kwargs):
         """
         Defines the computation performed at every call.