[Bug rtl-optimization/17935] Two consecutive movzbl are generated

["uros at kss-loka dot si" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From uros at kss-loka dot si  2005-05-13 10:07 -------
I think there is another optimization opportunity regarding movzbl following andl.

Consider this part:

        movb    (%eax), %al        EAX = x...xbbbbbbbb
        andl    $1, %eax           EAX = 0...00000000b
        movzbl  %al, %eax          (not needed)
        ret

If the value of the constant to andl operator is less than 2 ^ bit width of the
register we would like to extend, then andl instruction inherently performs
zero-extension.

So if the xorl in comment #5 is moved before andl, we could apply above
simplification to get:

        movb    (%eax), %al
        xorl    $1, %eax
        andl    $1, %eax
        ret

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17935