I was aware that OPs do kind of gotos to next-OPs (the ->label at the end of each line).

But it didn't seem logical that the -src option could be offered if B::Concise wasn't respecting the order.*

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

D:\tmp>type tst_b_xref3.pl
unless ($var1) {
    $var2++;
}
else {
    $var3++;
}
[download]

D:\tmp>perl -MO=Concise,-src tst_b_xref3.pl|find "var"
tst_b_xref3.pl syntax OK
# 1: unless ($var1) {
3              <#> gvsv[*var1] s ->4
# 5:     $var3++;
7                    <#> gvsv[*var3] s ->8
# 2:     $var2++;
d                    <#> gvsv[*var2] s ->e
[download]

So strictly speaking it's still possible to use B::Concise to emulate B::Xref on line number level.

*) Interestingly this also depends on the Perl version. Here the vars appear in order: (Ubuntu 5.18)

$ perl -MO=Concise,-src tst_b_xref3.pl|grep var
tst_b_xref3.pl syntax OK
# 1: unless ($var1) {
3                 <#> gvsv[*var1] s ->4
# 2:     $var2++;
8                    <#> gvsv[*var2] s ->9
# 5:     $var3++;
e                    <#> gvsv[*var3] s ->f
[download]

update

and that's the reason why, 5.24 is optimizing the negation away by swapping the branches:

D:\tmp>perl -MO=Deparse tst_b_xref3.pl
tst_b_xref3.pl syntax OK
if ($var1) {
    ++$var3;
}
else {
    ++$var2;
}
[download]