Regexp replaces using large replacement variables fail some of

Change #29619 fixes this bug for taint mode too. However, I
don't
understand why $ isn't compiled to the same optree with
-T and without:

[rafaelinv75-3-82-241-119-67 p4blead]$ ./perl -Ilib
-MO=Concise -e
'print $'
7  <> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
6     <> print vK ->7
3        <0> pushmark s ->4
5        <1> rv2sv sK/1 ->6
-           <> scope sK ->5
-              <0> ex-nextstate v ->4
4              <$> const(IV 10) s ->5
-e syntax OK
[rafaelinv75-3-82-241-119-67 p4blead]$ ./perl -TIlib
-MO=Concise -e
'print $'
a  <> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v:{ ->3
9     <> print vK ->a
3        <0> pushmark s ->4
8        <1> rv2sv sK/1 ->9
7           <> leave sK ->8
4              <0> enter s ->5
5              <;> nextstate(main 1 -e:1) v ->6
6              <$> const(IV 10) s ->7
-e syntax OK