Actually, pre-applying lc did not fare so well: 

use strict;
use warnings;
use Benchmark 'cmpthese';

my $string = 'TwAs BrIlLiG aNd ThE sLiThY tOvEs DiD gYrE aNd GiMbLe';

cmpthese( -1,
          {
             i_s => sub { local $_ =    $string; /gimble/i },
             I_s => sub { local $_ =    $string; /GiMbLe/  },
            lc_s => sub { local $_ = lc $string; /gimble/  },
             i_f => sub { local $_ =    $string; /foobar/i },
             I_f => sub { local $_ =    $string; /foobar/  },
            lc_f => sub { local $_ = lc $string; /foobar/  },
          }
        );
__END__
         Rate lc_f lc_s  i_s  I_s  i_f  I_f
lc_f 459364/s   --  -4% -13% -27% -33% -33%
lc_s 477204/s   4%   -- -10% -24% -30% -30%
i_s  530962/s  16%  11%   -- -15% -22% -22%
I_s  628278/s  37%  32%  18%   --  -8%  -8%
i_f  681314/s  48%  43%  28%   8%   --  -0%
I_f  681315/s  48%  43%  28%   8%   0%   --

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the lowliest monk

In reply to Re^2: Slowness of /i by tlm
in thread Slowness of /i by sulfericacid

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