* if ANDing with a constant of the form:

  0x00000..00FFF..FF
      ^      ^
      ^      ^
    any number of
    0's followed by
    some number of
    1's

    then we use dep.z to just paste zeros over the input. For the special
    cases where this is zxt1/zxt2/zxt4, we use those instructions instead,
    because we're all about readability!!!
    that's what it's about!! readability!

  *twitch* ;D

llvm-svn: 21279