Why do these 2 RegEx benchmarks differ so much?
# Benchmark
use Benchmark qw(:all);

my $count = 10000000;
my $re = qr/abc/o;
my %tests = (
    "NOFIND        " => "cvxcvidgds.sdfpkisd[s"
   ,"FIND_AT_END   " => "cvxcvidgds.sdfpabcd[s"
   ,"FIND_AT_START " => "abccvidgds.sdfpkisd[s"
);

foreach my $type (keys %tests) {
    my $str = $tests{$type};
    cmpthese($count, {
        "rege1.$type" => sub { my $idx = ($str =~ $re); },
        "rege2.$type" => sub { my $idx = ($str =~ /abc/o); }
    });
}

# Benchmark
use Benchmark qw(:all);

my $count = 10000000;
my $re = qr/abc/o;
my %tests = (
    "NOFIND        " => "cvxcvidgds.sdfpkisd[s"
   ,"FIND_AT_END   " => "cvxcvidgds.sdfpabcd[s"
   ,"FIND_AT_START " => "abccvidgds.sdfpkisd[s"
);

foreach my $type (keys %tests) {
    my $str = $tests{$type};
    cmpthese($count, {
        "rege1.$type" => sub { my $idx = ($str =~ $re); },
        "rege2.$type" => sub { my $idx = ($str =~ /abc/o); }
    });
}

use Benchmark 'cmpthese';

my $re = qr/abc/o;
my %tests = (
   'fail ' => 'cvxcvidgds.sdfpkisd[s',
   'end  ' => 'cvxcvidgds.sdfpabcd[s',
   'start' => 'abccvidgds.sdfpkisd[s',
);

for my $mag (map 10**$_, 1 .. 5) {
    say "n$mag:";
    for my $type (keys %tests) {
        my $str = $tests{$type};
        cmpthese -1, {
            '$re    '.$type => sub {my $i; $i = ($str =~ $re   ) for 0 .. $mag},
            '/abc/o '.$type => sub {my $i; $i = ($str =~ /abc/o) for 0 .. $mag},
            '/$re/  '.$type => sub {my $i; $i = ($str =~ /$re/ ) for 0 .. $mag},
            '/$re/o '.$type => sub {my $i; $i = ($str =~ /$re/o) for 0 .. $mag},
        }
    }
}

/.../o

1/661157 s - 1/4384042 s = 0.000,001,3 s
1/678702 s - 1/5117707 s = 0.000,001,3 s
1/657765 s - 1/4268032 s = 0.000,001,3 s

>perl -MO=Concise,-exec -e"$x =~ /abc/"
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <#> gvsv[*x] s
4  </> match(/"abc"/) vKS/RTIME
5  <@> leave[1 ref] vKP/REFC
-e syntax OK

>perl -MO=Concise,-exec -e"$x =~ $re"
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <#> gvsv[*x] s
4  <1> regcreset sK/1
5  <#> gvsv[*re] s
6  <|> regcomp(other->7) sK/1
7  </> match() vKS/RTIME
8  <@> leave[1 ref] vKP/REFC
-e syntax OK