check whether scalar condition var is on CPU before using

paddle/fluid/operators/conditional_block_op.cc

@@ -54,7 +54,18 @@ class ConditionalOp : public framework::OperatorBase {
           "numel should be 1, actual numel is %d",
           ips[0]->numel());
     }
-    return ips[0]->data<bool>()[0];
+    bool res;
+    if (platform::is_gpu_place(ips[0]->place())) {
+#ifdef PADDLE_WITH_CUDA
+      framework::LoDTensor cpu_tensor;
+      framework::TensorCopy(*ips[0], platform::CPUPlace(), &cpu_tensor);
+      platform::DeviceContextPool::Instance().Get(ips[0]->place())->Wait();
+      res = cpu_tensor.data<bool>()[0];
+#endif
+    } else {
+      res = ips[0]->data<bool>()[0];
+    }
+    return res;
   }
 };