Fix broadcast

Author: chengduoZH

paddle/fluid/framework/details/broadcast_op_handle.cc

@@ -73,6 +73,9 @@ void BroadcastOpHandle::RunImpl() {
     int root_id = boost::get<platform::CUDAPlace>(in_tensor.place()).device;
     std::vector<std::function<void()>> broadcast_calls;
 
+    int type = platform::ToNCCLDataType(in_tensor.type());
+    size_t numel = static_cast<size_t>(in_tensor.numel());
+
     for (auto out_var_handle : out_var_handles) {
       Variable *out_var = var_scopes.at(out_var_handle->scope_idx_)
                               ->FindVar(out_var_handle->name_);
@@ -87,13 +90,11 @@ void BroadcastOpHandle::RunImpl() {
         send_recv_buffer = const_cast<void *>(in_tensor.data<void>());
         out_handle = out_var_handle;
       } else {
-        send_recv_buffer =
-            VariableVisitor::GetMutableTensor(out_var).mutable_data(
-                out_var_handle->place_);
+        send_recv_buffer = VariableVisitor::GetMutableTensor(out_var)
+                               .Resize(in_tensor.dims())
+                               .mutable_data(out_var_handle->place_);
       }
 
-      int type = platform::ToNCCLDataType(in_tensor.type());
-      size_t numel = static_cast<size_t>(in_tensor.numel());
       broadcast_calls.emplace_back(
           [send_recv_buffer, numel, type, root_id, &nccl_ctx] {
             PADDLE_ENFORCE(platform::dynload::ncclBcast(