To back up what I said,

>perl -MO=Concise,-exec -e"(LIST_EXPR)[INDEX_EXPR]"
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <0> pushmark s
4  <$> const[PV "INDEX_EXPR"] s/BARE
5  <0> pushmark s
6  <$> const[PV "LIST_EXPR"] s/BARE
7  <2> lslice vK/2
8  <@> leave[1 ref] vKP/REFC
-e syntax OK
[download]

Or a more à propos example,

>perl -MO=Concise,-exec -e"(split)[$x..$y]"
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <0> pushmark s
4  <|> range(other->5)[t5] lK/1        <--------
5      <#> gvsv[*y] s
6      <1> flop lK
           goto 7
e  <#> gvsv[*x] s
f  <1> flip[t6] lK
7  <0> pushmark s
8  </> pushre(/" "/) s*/64
9  <#> gvsv[*_] s
a  <$> const[IV 0] s
b  <@> split[t2] lK                    <--------
c  <2> lslice vK/2
d  <@> leave[1 ref] vKP/REFC
-e syntax OK
[download]

Now, I suspect the relative order in which the expressions are evaluated is arbitrary. It could be changed if it would be deemed useful to evaluate them in the other order.