diotalevi: I didn't mean the copy at the start, but these ones in the benchmark loop:

my @permuted = @ary[0..$i-1, $j, $i+1..$j-1, $i, $j+1..$len];
# and
my @permuted = @ary;
@permuted[$i, $j] = @permuted[$j, $i];
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(and the ones for @ary2, obviously)

In other words, the operation in the benchmark IS a copy operation.