[Bug middle-end/18038] addition in a multibit bitfield is inefficient

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18038

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-02-18 
20:32:51 UTC ---
We generated now:
    .cfi_startproc
    movzbl    (%eax), %ecx
    addl    %ecx, %edx
    andl    $-4, %ecx
    andl    $3, %edx
    orl    %edx, %ecx
    movb    %cl, (%eax)
    ret