D:\tmp>more tst_b_xref2.pl
use strict;
use warnings;
my $sth;

while ( my @row =$sth->fetchrow) {    #:5 intro
    print "@row";                     #:6 used
}

##</code><code>##

D:\tmp>perl -MO=Xref,-r,-d,-DO tst_b_xref2.pl
OP (0x163e650) enter
COP (0x10fcdd8) nextstate
OP (0x10fce38) padsv
tst_b_xref2.pl   (main)           3 (lexical)       $ sth              intro
COP (0x163e698) nextstate
LOOP (0x163e740) enterloop
OP (0x16579c8) pushmark
OP (0x1657a50) pushmark
PADOP (0x1657b48) gvsv
tst_b_xref2.pl   (main)           5 main            $ "                used
OP (0x1657ad0) padav
tst_b_xref2.pl   (main)           5 (lexical)       @ row              used  #:used?
LISTOP (0x1657a88) join
LISTOP (0x1657a08) print
OP (0x163e870) unstack
OP (0x1657bd0) pushmark
OP (0x1657d60) pushmark
OP (0x10fcd18) padsv
tst_b_xref2.pl   (main)           5 (lexical)       $ sth              used     
METHOP (0x1657d18) method_named
UNOP (0x1657cd0) entersub
tst_b_xref2.pl   (main)           5 (lexical)       $ sth              subused
OP (0x1657c50) pushmark
OP (0x10fcd58) padav
tst_b_xref2.pl   (main)           5 (lexical)       @ row              intro #:5?intro?
BINOP (0x1657b88) aassign
LOGOP (0x163e7e0) and
BINOP (0x163e6f8) leaveloop
LISTOP (0x10fcd90) leave
tst_b_xref2.pl syntax OK

##</code><code>##

D:\tmp>perl -MO=Concise,-src tst_b_xref2.pl
n  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
# 3: my $sth;
2     <;> nextstate(main 3 tst_b_xref2.pl:3) v:*,&,{,x*,x&,x$,$ ->3
3     <0> padsv[$sth:3,9] vM/LVINTRO ->4
# 5: while ( my @row =$sth->fetchrow) {                             #:line 5
4     <;> nextstate(main 4 tst_b_xref2.pl:5) v:*,&,{,x*,x&,x$,$ ->5
m     <2> leaveloop vK/2 ->n
5        <{> enterloop(next->c last->m redo->6) v ->d
-        <1> null vK/1 ->m
l           <|> and(other->6) vK/1 ->m
k              <2> aassign[t4] sKS/COM_AGG ->l
-                 <1> ex-list lK ->i
d                    <0> pushmark s ->e
h                    <1> entersub[t3] lKS/TARG,STRICT ->i
e                       <0> pushmark s ->f
f                       <0> padsv[$sth:3,9] sM ->g
g                       <.> method_named[PV "fetchrow"] l ->h
-                 <1> ex-list lK ->k
i                    <0> pushmark s ->j
j                    <0> padav[@row:5,8] lRM*/LVINTRO ->k           #:@row intro
-              <@> lineseq vK ->-
-                 <@> scope vK ->c
# 6:     print "@row";                                              #:line 6
-                    <;> ex-nextstate(main 7 tst_b_xref2.pl:6) v:*,&,x*,x&,x$,$ ->6
b                    <@> print vK ->c
6                       <0> pushmark s ->7
a                       <@> join[t6] sK/2 ->b
7                          <0> pushmark s ->8
-                          <1> ex-rv2sv sK/STRICT,1 ->9
8                             <#> gvsv[*"] s ->9
9                          <0> padav[@row:5,8] l ->a                #:@row used
c                 <0> unstack v ->d
tst_b_xref2.pl syntax OK