[Bug target/81664] __attribute__((target("movbe"))) does not work

[bugzilla@poradnik-webmastera.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81664

--- Comment #2 from Daniel Fruzynski <bugzilla@poradnik-webmastera.com> ---
So there is another problem here: for some reason both mentioned gcc versions
accepts -mmovbe and -mno-movbe options. If movbe is not supported, gcc should
complain that these options are unrecognized.

I also checked generated assembly code and there are no movbe instruction
there. However I noticed that gcc 4.8.5 on Redhat 7 generates different code
when -mmovbe is used - it adds extra instruction marked below with ***.

_Z11ntohl_movbel:
.LFB6:
        .cfi_startproc
        movl    %edi, %eax
        bswap   %eax
        movl    %eax, %eax   ***
        ret
        .cfi_endproc