my %comboHashRef = %{$_[2]};

##</code><code>##

my %comboHashRef = %{$_[2]};
...
foreach my $key (keys %comboHashRef){

##</code><code>##

my $comboHashRef = $_[2];
...
foreach my $key (keys %{ $comboHashRef } ){

##</code><code>##

my $comboHashRef = $_[2];
...
while( my( $key, $value ) = each %{ $comboHashRef } ){


##</code><code>##

return %precords;

##</code><code>##

sub yourWay{ 
    my %h = %{ $_[0] }; 
    return %h; 
};;

sub myWay{ 
    my $ref = shift; 
    return $ref 
};;

%hash = ( 1 .. 1e6 );;

cmpthese -5,{
    a=>q[ 
        my %h = yourWay( \%hash ); 
    ], 
    b=>q[ 
        my $h = myWay( \%hash ); 
    ] 
};;
     s/iter          a          b
a      1.12         --      -100%
b 1.03e-006 108368213%         --