You can iterate over the hash, and build a new one: 
my %uniq;
for (keys %hash){
    if (exists $uniq{scalar reverse $_}){
        $uniq{scalar reverse $_} += $hash{$_};
    } else {
        $uniq{$_} = $hash{$_};
    }
}
# untested

[download]

Note that the outcome will either contain the key 'AB' or 'BA', but you don't have control over which one occurs (it's not in the spec ;-)

In reply to Re: confused with a hash which contains reversed keys by moritz
in thread confused with a hash which contains reversed keys by Anonymous Monk

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