Loop Rewind - Return Type - 2022.2 English

Vitis HLS Messaging (UG1448)

Document ID
UG1448
Release Date
2022-12-16
Version
2022.2 English

Description

Warning: [200-958] Unable to rewind loop %s: function has no return.
This message reports that the code is violating loop rewind optimization rules.

Explanation

Loop rewind optimization requires the function return to either be void or have a return statement.

The following example will fail optimization.

int decoderInput(hls::stream<mag_type> &inputStream, hls::stream<dataPair> &pairedData)//, hls::stream<int> &windex)
{
    static count_type cnt;
    mag_type val, val_next;
    dataPair tempData;
    int n=0;
        decoderInput_whileloop:while(1)
        {
    #pragma HLS PIPELINE II=1 rewind
            if(!inputStream.empty())
            {
                if(cnt==0)
                {
                     tempData.even = inputStream.read();
                     cnt =1;
                }
                else
                {
                    tempData.odd=inputStream.read();
                    pairedData.write(tempData);
                    cnt=0;
                }
            }
            else
            {
                break;
 
            }
        }
}

Solution

The loop rewind optimization requires the function return type to either be void or have a return statement.