Code is:

use strict;
use warnings;

use Benchmark qw(cmpthese);

# No taint implications.
sub A { s/^\s*//; s/\s*$//; return $_; }

# These untaint the return value.
sub B { m/^\s*(.*\S)\s*$/;  return $1; }
sub C { m/(\S+.*\S*)/;      return $1; }
sub D { m/(\S?.*\S*)/;      return $1; }

my @data = (
            'hello', ' hello', ' hello ',
            'hello hello', ' hello hello', 'hello hello ',
            ' hello hello',    '  hello  hello  ',
            'h', ' h', 'h ', ' h ',
            "\n\t hello \n\t"
);

for (@data) {

  my $A = A( $_ );   my $B = B( $_ );
  my $C = C( $_ );   my $D = D( $_ );

  unless ( $A eq $B && $A eq $C && $A eq $D ) {
    warn "Found a disagreement\n";
    warn "\tA is '$A'\n\tB is '$B'\n\tC is '$C'\n\tD is '$D'\n\n";
  } 
  
  if ( $A =~ m/(^\s|\s$)/ ) {
    warn "Regexp not working\n\tA is '$A'\n\n";
  }
}

cmpthese( -3,
          { 
           A => sub { for (@data) { A( $_ ); }},
           B => sub { for (@data) { B( $_ ); }},
           C => sub { for (@data) { C( $_ ); }},
           D => sub { for (@data) { D( $_ ); }},
          });
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