The solution is that the source lines they are not in order, but the line numbers are still reliable:

$ cat /tmp/p
for (
    $var1++;
    $var2++;
    $var3++
) {
    $var4++;
}


$ perl -MO=Concise,-src /tmp/p | grep var
/tmp/p syntax OK
3           <#> gvsv[*var1] s ->4
f                    <#> gvsv[*var2] s ->g
# 6:     $var4++;
9                          <#> gvsv[*var4] s ->a
c                       <#> gvsv[*var3] s ->d
[download]

Dave.