In case it helps, warn gets its info from the most recently executed nextstate op.

$ perl -e'
   if ($false) {   # This is line 2
   }
   elsif (warn) {  # This is line 4
   }
'
Warning: something's wrong at -e line 2.

$ perl -MO=Concise -e'
   if ($false) {   # This is line 2
   }
   elsif (warn) {  # This is line 4
   }
'
6  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 4 -e:2) v ->3
-     <1> null vKP/1 ->6
4        <|> cond_expr(other->5) vK/1 ->7
-           <1> ex-rv2sv sK/1 ->4
3              <#> gvsv[*false] s ->4
-           <@> scope vK ->-
5              <0> stub v ->6
-           <1> null vK/1 ->-
9              <|> and(other->a) vK/1 ->6
8                 <@> warn[t2] sK ->9
7                    <0> pushmark s ->8
-                 <@> scope vK ->-
a                    <0> stub v ->6
-e syntax OK
[download]