>perl -MO=Concise,f -e"sub f { return $x }"
main::f:
5  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <@> lineseq KP ->5
1        <;> nextstate(main 1 -e:1) v ->2
4        <@> return K ->5
2           <0> pushmark s ->3
-           <1> ex-rv2sv sK/1 ->4
3              <#> gvsv[*x] s ->4
-e syntax OK

##</code><code>##

main::f:
3  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <@> lineseq KP ->5
1        <;> nextstate(main 1 -e:1) v ->2
-        <@> ex-return K ->-
-           <0> ex-pushmark s ->-
-           <1> ex-rv2sv sK/1 ->-
2              <#> gvsv[*x] s ->3
-e syntax OK

##</code><code>##

>perl -MO=Concise,f -e"sub f { $x }"
main::f:
3  <1> leavesub[1 ref] K/REFC,1 ->(end)
-     <@> lineseq KP ->3
1        <;> nextstate(main 1 -e:1) v ->2
-        <1> ex-rv2sv sK/1 ->-
2           <#> gvsv[*x] s ->3
-e syntax OK

##</code><code>##

5.8.8:
           Rate implicit explicit
implicit 980/ms       --      -0%
explicit 984/ms       0%       --

5.10.0:
            Rate explicit implicit
explicit 1000/ms       --      -0%
implicit 1004/ms       0%       --

##</code><code>##

use strict;
use warnings;

use Benchmark qw( cmpthese );

my $OUTER = $ARGV[0] || -3;
my $INNER = $ARGV[1] || 1000;

sub explicit { return $_[0] }
sub implicit {        $_[0] }

my %tests = map { $_ => "use strict;
                         use warnings;
                         for (1..$INNER) {
                            my \$rv = $_(1);
                         }
                        "
                }
              qw( explicit implicit );

cmpthese($OUTER, \%tests);
print("\n");
print("Multiply by $INNER to get real rate.\n");