s{^\x{feff}*<!-- HINT.*? -->}{};

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

use Encode;
use Benchmark qw(:all);

binmode(STDOUT, ":utf8");

#my $xmlcmt = "<!-- HINT: Some XML comments to be deleted -->";
my $xmlcmt = ""; 
my $str_lat = "My \x{20AC}0.02 of info";
my $str_ara = decode_utf8("\xd8\xa7\xd9\x84\xd8\xa3\xd9\x86\xd8\xb4\xd8\xb7\xd8\xa9");


print Encode::is_utf8($str_lat) ? "Is_utf8" : "Not_utf8", "\t";  print $str_lat, "\n";
print Encode::is_utf8($str_ara) ? "Is_utf8" : "Not_utf8", "\t";  print $str_ara, "\n";

timethese(2, {
    "ara nocmt 1step" => sub { s1($str_ara) },
    "ara nocmt 2step" => sub { s2($str_ara) },
    "ara w-cmt 1step" => sub { s1($xmlcmt . $str_ara) },
    "ara w-cmt 2step" => sub { s2($xmlcmt . $str_ara) },
    "lat nocmt 1step" => sub { s1($str_lat) },
    "lat nocmt 2step" => sub { s2($str_lat) },
    "lat w-cmt 1step" => sub { s1($xmlcmt . $str_lat) },
    "lat w-cmt 2step" => sub { s2($xmlcmt . $str_lat) },
 
});

# Do the replacement in 1 step
sub s1
{
    my $s = shift;
    #$s =~ s{^\x{feff}*<!-- .*? -->}{};         # This is fast
    #$s =~ s{^\x{feff}*<!-- Hi.*? -->}{};       # This is fast
    #$s =~ s{^\x{feff}?<!-- HINT.*? -->}{};     # This is fast
    $s =~ s{^\x{feff}*<!-- HINT.*? -->}{};      # This could be slow
}

# Do the replacement in 2 steps
sub s2
{
    my $s = shift;
    $s =~ s{^\x{feff}*}{};
    $s =~ s{^<!-- HINT.*? -->}{};
}