[Bug tree-optimization/56770] New: Partial sums loop optimization

[dje at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56770



             Bug #: 56770

           Summary: Partial sums loop optimization

    Classification: Unclassified

           Product: gcc

           Version: 4.9.0

            Status: UNCONFIRMED

          Severity: enhancement

          Priority: P3

         Component: tree-optimization

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: d...@gcc.gnu.org





GCC loop optimization should unroll and transform loops using partial sums

where beneficial for expensive, independent computations where the target has

additional function units available.



Before



    double fValue = 0;

    int j;

    for (j = 0; j < NZ; j++)

        fValue += Q[j] / r[j];



After



    double fValue = 0;

    double fValue1 = 0;

    int j;

    for (j = 0; j < NZ; j=j+2){

        fValue += Q[j] / r[j];

        fValue1 += Q[j+1] / r[j+1];

    }



    for (j = (NZ/2)*2; j < NZ; j++){

        fValue += Q[j] / r[j];

    }



    fValue = fValue + fValue1;