[Bug tree-optimization/57488] [4.9 regression] loop terminates early at -O3

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57488

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
-fno-tree-partial-pre fixes this, partial PRE figures that v on entry to the
l loop is invariant in the outer loop.  Thus it does

    tem = v;
    for (k = 1; k >= 0; k--)
    {
        int l;
        bar (0);
        v = tem;
        for (l = 1; l < 5; l++)
        {
            int m;
            for (m = 6; m; m--)
            {
                v--;
                *ps = *pc;
            }
        }
    }

effectively cutting the number of decrements in half.