$n = 1e0; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
       Rate    b    a
b 1000796/s   -- -60%
a 2493375/s 149%   --

$n = 1e1; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
       Rate    b    a
b  234727/s   -- -87%
a 1838169/s 683%   --

$n = 1e2; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y]; ],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g; ] 
};;
      Rate     b     a
b  28926/s    --  -95%

a 585631/s 1925%    --
$n = 1e3; 
cmpthese -1,{
    a => q[ my $s='axb'; $s x= $n; $s=~tr[x][y];],
    b => q[ my $s='axb'; $s x= $n; $s=~s[x][y]g;] 
};;
     Rate     b     a
b  3087/s    --  -96%
a 76540/s 2379%    --