Just like we use the RHS of an AND to simplify the LHS, use the LHS to

simplify the RHS.  This allows for the elimination of many thousands of
ands from multisource, and compiles CodeGen/PowerPC/and-elim.ll:test2
into this:

_test2:
        srwi r2, r3, 1
        xori r3, r2, 40961
        blr

instead of this:

_test2:
        rlwinm r2, r3, 31, 17, 31
        xori r2, r2, 40961
        rlwinm r3, r2, 0, 16, 31
        blr

llvm-svn: 26388