$ perl -MO=Concise,-exec -e'@NAMESPACE::data = split / /, $x'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  </> pushre(/" "/ => @data) s/64
4  <#> gvsv[*x] s
5  <$> const[IV 0] s
6  <@> split[t4] vK
7  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'@data = split / /, $x'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  </> pushre(/" "/ => @data) s/64
4  <#> gvsv[*x] s
5  <$> const[IV 0] s
6  <@> split[t4] vK
7  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'my @data; @data = split / /, $x'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v
3  <0> padav[@data:1,2] vM/LVINTRO
4  <;> nextstate(main 2 -e:1) v
5  <0> pushmark s
6  </> pushre(/" "/) s/64
7  <#> gvsv[*x] s
8  <$> const[IV 0] s
9  <@> split[t3] lK
a  <0> pushmark s
b  <0> padav[@data:1,2] lRM*
c  <2> aassign[t4] vKS
d  <@> leave[1 ref] vKP/REFC
-e syntax OK
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See above that the array assignment is completely bypassed; instead the array is attached in a funny kind of way to the regex which is then passed to split, and split places the results directly into the array instead of returning them.