Implement logical and with an immediate that consists of a contiguous block

of one or more 1 bits (may wrap from least significant bit to most
significant bit) as the rlwinm rather than andi., andis., or some longer
instructons sequence.

int andn4(int z) { return z & -4; }
int clearhi(int z) { return z & 0x0000FFFF; }
int clearlo(int z) { return z & 0xFFFF0000; }
int clearmid(int z) { return z & 0x00FFFF00; }
int clearwrap(int z) { return z & 0xFF0000FF; }

_andn4:
        rlwinm r3, r3, 0, 0, 29
        blr

_clearhi:
        rlwinm r3, r3, 0, 16, 31
        blr

_clearlo:
        rlwinm r3, r3, 0, 0, 15
        blr

_clearmid:
        rlwinm r3, r3, 0, 8, 23
        blr

_clearwrap:
        rlwinm r3, r3, 0, 24, 7
        blr

llvm-svn: 16832