[Bug target/93002] while(i--) optimization

[getchar_gnu at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93002

--- Comment #7 from getchar_gnu at hotmail dot com ---
Actually for `while (i--) sink=i;` with knowledge that `i!=0` it's valid to
compile as
    .L11:
        subl    $1, %edi
        movl    %edi, sink(%rip)
        jne     .L11
        ret
which can be made with c code `while(sink=--i);` (leaving different resulting
i)