Surprised to get "converted into an equivalent circuit" warning

Hi Folks-

 
Warning (13310): Register "MPS_SOPC:inst|pulse_engine_0:the_pulse_engine_0|pulse_engine:pulse_engine_0|sample_delay:delay|mem" is converted into an equivalent circuit using register "MPS_SOPC:inst|pulse_engine_0:the_pulse_engine_0|pulse_engine:pulse_engine_0|sample_delay:delay|mem~_emulated" and latch "MPS_SOPC:inst|pulse_engine_0:the_pulse_engine_0|pulse_engine:pulse_engine_0|sample_delay:delay|mem~latch"

 
`define BUFFER_SIZE 64
 
module sample_delay(
  input wire reset_n, // Reset
  input wire adc_clock, // Sample clock
  input wire  adc_data, // Input sample
  output wire  adc_data_delayed // Delayed sample
);
 
  reg  mem;
  integer i;
 
  initial
  begin
    for(i = 0; i < `BUFFER_SIZE; i = i + 1) mem = 14'd0;
  end
 
  assign adc_data_delayed = mem;
 
  always @(posedge adc_clock or negedge reset_n)
  begin
    if(~reset_n)
    begin
      for(i = 0; i < `BUFFER_SIZE; i = i + 1) mem <= adc_data;
    end
    else
    begin
      mem <= adc_data;   // <--- COMPLAINS HERE AND NEXT LINE
      for(i = 1; i < `BUFFER_SIZE; i = i + 1) mem <= mem;
    end
  end
 
endmodule