[cherry-pick] Fix amp support fleet(#29505)

Author: Aurelius84

python/paddle/fluid/contrib/mixed_precision/decorator.py

@@ -66,6 +66,8 @@ def __init__(self, optimizer, amp_lists, init_loss_scaling,
         self._loss_scaling = None
         self._init_loss_scaling = init_loss_scaling
         self._use_dynamic_loss_scaling = use_dynamic_loss_scaling
+        self._learning_rate = optimizer._learning_rate
+        self._learning_rate_map = optimizer._learning_rate_map
         if self._use_dynamic_loss_scaling:
             self._incr_every_n_steps = incr_every_n_steps
             self._decr_every_n_nan_or_inf = decr_every_n_nan_or_inf

python/paddle/fluid/optimizer.py

@@ -3751,7 +3751,9 @@ def __init__(self, optimizer, num_microbatches=1, start_cpu_core_id=0):
         if framework.in_dygraph_mode():
             raise Exception("In dygraph, don't support PipelineOptimizer.")
         if not isinstance(optimizer, Optimizer) and not isinstance(
-                optimizer, paddle.optimizer.Optimizer):
+                optimizer, paddle.optimizer.Optimizer) and not isinstance(
+                    optimizer, paddle.fluid.contrib.mixed_precision.decorator.
+                    OptimizerWithMixedPrecision):
             raise ValueError("The 'optimizer' parameter for "
                              "PipelineOptimizer must be an instance of "
                              "Optimizer, but the given type is {}.".format(