I've just tried that but it errors out with Modification of non-creatable array value attempted, subscript -2 at (eval 11) line 1.. Here's the code:

#!/usr/bin/env perl 
use strict;
use warnings;
use Benchmark 'cmpthese';

for my $arrsize (1e4, 1e6, 1e8) {
    print "Source array has $arrsize elements\n";
    my @x;
    push @x, rand for 1..$arrsize;

    cmpthese (1e7, {
        'BUK' => ' my @y; $y[ $_-1 ] = $x[ $_-1 ] - $x[ $_ ] for 1 .. 
+$#x; ',
        'ike1' => ' my @y; $y[ $_ ] = $x[ $_ ] - $x[ $_+1 ] for 0 .. $
+#x-1; ',
        'ike2' => ' my @y = @x; $y[ $_ ] -= $y[ $_+1 ] for 0 .. $#y-1;
+ pop @y; ',
        'while' => ' my @y; my $i = $#x; $y[ $i ] = $x[ $i ] + $x[ --$
+i ] while $i; ',
    });
    print '-' x 80 . "\n";
}
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I'm not sure how it manages to get down to -2. Have I mis-typed your "while" version?