Refine cast op (#8923)

* fix mac build error

* override GetExpectedKernelType for cast op

* fix typo

* add cuda unittest

paddle/fluid/operators/cast_op.cc

@@ -63,13 +63,27 @@ class CastOpGradMaker : public framework::SingleGradOpDescMaker {
   }
 };
 
+class CastOp : public framework::OperatorWithKernel {
+ public:
+  using framework::OperatorWithKernel::OperatorWithKernel;
+
+ protected:
+  framework::OpKernelType GetExpectedKernelType(
+      const framework::ExecutionContext &ctx) const override {
+    framework::OpKernelType kt = OperatorWithKernel::GetExpectedKernelType(ctx);
+    // CastOp kernel's device type is decided by input tensor place
+    kt.place_ = ctx.Input<framework::LoDTensor>("X")->place();
+    return kt;
+  }
+};
+
 }  // namespace operators
 }  // namespace paddle
 
 namespace ops = paddle::operators;
 using CPU = paddle::platform::CPUDeviceContext;
-REGISTER_OP_WITH_KERNEL(cast, ops::CastOpGradMaker, ops::CastOpInferShape,
-                        ops::CastOpProtoMaker);
+REGISTER_OPERATOR(cast, ops::CastOp, ops::CastOpGradMaker,
+                  ops::CastOpInferShape, ops::CastOpProtoMaker);
 REGISTER_OP_CPU_KERNEL(cast, ops::CastOpKernel<CPU, float>,
                        ops::CastOpKernel<CPU, double>,
                        ops::CastOpKernel<CPU, int>,

python/paddle/fluid/tests/unittests/test_learning_rate_scheduler.py

@@ -19,6 +19,7 @@ import unittest
 import paddle.fluid as fluid
 import paddle.fluid.layers as layers
 import paddle.fluid.framework as framework
+import paddle.fluid.core as core
 
 
 def exponential_decay(learning_rate,
@@ -81,6 +82,16 @@ def piecewise_decay(global_step, boundaries, values):
 
 class TestLearningRateDecay(unittest.TestCase):
     def check_decay(self, python_decay_fn, fluid_decay_fn, kwargs):
+        places = [fluid.CPUPlace()]
+        if core.is_compiled_with_cuda():
+            places.append(fluid.CUDAPlace(0))
+        for place in places:
+            self.check_decay_with_place(place, python_decay_fn, fluid_decay_fn,
+                                        kwargs)
+
+    def check_decay_with_place(self, place, python_decay_fn, fluid_decay_fn,
+                               kwargs):
+
         decayed_lr = fluid_decay_fn(**kwargs)
 
         place = fluid.CPUPlace()