[Bug target/93006] Better code with a-- == 0 rather than --a == -1

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93006

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
But even bar is unnecessarily long:
        movl    a(%rip), %edx
        leal    -1(%rdx), %eax
        cmpl    $1, %edx
        movl    %eax, a(%rip)
        movl    %edi, %eax
        adcl    %esi, %eax
        ret
We could use
        movl    a(%rip), %edx
        subl    $1, %edx
        movl    %edx, a(%rip)
        movl    %edi, %eax
        adcl    %esi, %eax
        ret
or even
        subl    $1, a(%rip)
        movl    %edi, %eax
        adcl    %esi, %eax
        ret