When loops are used in C++ classes, care should be taken to ensure that the loop induction variable is not a data member of the class as this prevents the loop from being unrolled.
In this example, loop induction variable k
is a member of class
foo_class
.
template <typename T0, typename T1, typename T2, typename T3, int N>
class foo_class {
private:
pe_mac<T0, T1, T2> mac;
public:
T0 areg;
T0 breg;
T2 mreg;
T1 preg;
T0 shift[N];
int k; // Class Member
T0 shift_output;
void exec(T1 *pcout, T0 *dataOut, T1 pcin, T3 coeff, T0 data, int col)
{
Function_label0:;
#pragma HLS inline off
SRL:for (k = N-1; k >= 0; --k) {
#pragma HLS unroll // Loop will fail UNROLL
if (k > 0)
shift[k] = shift[k-1];
else
shift[k] = data;
}
*dataOut = shift_output;
shift_output = shift[N-1];
}
*pcout = mac.exec1(shift[4*col], coeff, pcin);
};
For Vitis HLS to be able to unroll the loop as
specified by the UNROLL pragma directive, the code should be rewritten to remove k
as a class member.
template <typename T0, typename T1, typename T2, typename T3, int N>
class foo_class {
private:
pe_mac<T0, T1, T2> mac;
public:
T0 areg;
T0 breg;
T2 mreg;
T1 preg;
T0 shift[N];
T0 shift_output;
void exec(T1 *pcout, T0 *dataOut, T1 pcin, T3 coeff, T0 data, int col)
{
Function_label0:;
int k; // Local variable
#pragma HLS inline off
SRL:for (k = N-1; k >= 0; --k) {
#pragma HLS unroll // Loop will unroll
if (k > 0)
shift[k] = shift[k-1];
else
shift[k] = data;
}
*dataOut = shift_output;
shift_output = shift[N-1];
}
*pcout = mac.exec1(shift[4*col], coeff, pcin);
};