It looks like the thing that surprises you is that you are paying the price for the special vars, when you haven't been using them. But it can't tell for sure that you won't have something like: 
my $one = one;
eval "uncomment_$one()";

[download]
So it has to play safe. Note that the following code goes wrong, because it can't see the magic var. 
'abc' =~ m/b/;
print( eval( '$`') , "\n")

[download]

In reply to Re: Impact of special variables on regex match performance by markhh
in thread Impact of special variables on regex match performance by roubi

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