Fold (x & 8) != 0 and (x & 8) == 8 into (x & 8) >> 3.

This turns this PPC code:

        rlwinm r2, r3, 0, 28, 28
        cmpwi cr7, r2, 8
        mfcr r2
        rlwinm r3, r2, 31, 31, 31

into this:

        rlwinm r2, r3, 0, 28, 28
        srwi r2, r2, 3
        rlwinm r3, r2, 0, 31, 31

Next up, nuking the extra and.

llvm-svn: 21390