[Bug tree-optimization/36009] New: PRE causes missed loop store motion, store sinking doesn't work

[rguenth at gcc dot gnu dot org]

double a[16][64], y[64], x[16];
void foo(void)
{
  int i, j;
  for (j = 0; j < 64; ++j)
    for (i = 0; i < 16; ++i)
      y[j] = y[j] + a[i][j] * x[i];
}

PRE moves the load of y[j] out of the inner loop like

    pretmp = y[j];
    for (i = 0; i < 16; ++i)
      {
        D.xxx = pretmp + a[i][j] * x[i];
        storetmp = D.xxx;
        y[j] = storetmp;
      }

which makes loop store motion no longer apply (store sinking is too
broken to fix this as well).


-- 
           Summary: PRE causes missed loop store motion, store sinking
                    doesn't work
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Keywords: missed-optimization
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: rguenth at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36009