Whatever code snippets you supply to benchmark, get wrapped internally into subs

That's true. That's why I usually do

$_ = "use strict; use warnings; for (1..10_000) { my \$x = '|0|0|0|0|0
+|0|'; $_ }";
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to minimize the cost of that sub call.

Also, I'm not sure what the cost of use strict; and use warnings is, when they have already been loaded,

Zero. use is executed once, at compile-time. It doesn't generate any code in the tree.

>perl -MO=Concise -e"use strict; print 'a'"
6  <@> leave[1 ref] vKP/REFC ->(end)
1     <0> enter ->2
2     <;> nextstate(main 2 -e:1) v/2 ->3
5     <@> print vK ->6
3        <0> pushmark s ->4
4        <$> const[PV "a"] s ->5
-e syntax OK
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