$ cat foo.pl ; echo "--------";echo; ./foo.pl 
#!/usr/bin/perl 
##################
use Benchmark qw(:all) ;

sub test1(){
$entries = @{[ split ]};
}

sub test2(){
$entries = () = /\S+/g;
}

$_="This is an example string with several words bla bla bla\n";
$count=1E+7;
timethis ($count, "test1()");
print "------------\n";
timethis ($count, "test2()");


--------

timethis 10000000: 13 wallclock secs (12.37 usr +  0.01 sys = 12.38 CP
+U) @ 807754.44/s (n=10000000)
------------
timethis 10000000:  7 wallclock secs ( 6.66 usr +  0.00 sys =  6.66 CP
+U) @ 1501501.50/s (n=10000000)
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Adding use warnings; results in

Use of uninitialized value in split at foo.pl line 9.
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Hmmm... adding (-l and) print $entries to both subs results in:

Use of uninitialized value in split at foo.pl line 9.
0
Use of uninitialized value in pattern match (m//) at foo.pl line 14.
0
[download]

Now,

#!/usr/bin/perl

use strict;
use warnings;
use Benchmark qw(:all :hireswallclock);

my $str="This is an example string with several words bla bla bla";

sub test1 () {
    local $_=$str;
    my $entries = @{[ split ]};
}

sub test2 () {
    local $_=$str;
    my $entries = () = /\S+/g;
}

cmpthese -10, {
    deref => \&test1,
    goatse => \&test2,
};

__END__
[download]

results in

          Rate goatse  deref
goatse 16325/s     --   -42%
deref  28017/s    72%     --
[download]