[Beignet] CL_MEM_USE_HOST_PTR involve extra copy?

[spring_wind]

Hi:
Intel opencl optimization guide said using CL_MEM_USE_HOST_PTR can avoid extra copy between CPU and GPU, but I noticed that in beignet's implementation source it was not like that:
/* Copy the data if required */
  if (flags & CL_MEM_COPY_HOST_PTR || flags & CL_MEM_USE_HOST_PTR)
    cl_buffer_subdata(mem->bo, 0, sz, data);


Could someone give me an answer?
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