What is the problem of keeping two separate hashes?

my %hash=(a => 'foo', b => 'bar', c => 'baz');
my %reverse;
@reverse{values %hash}=keys %hash; # if(f) values are unique, as you c
+laim.
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If what bothers you is having "two" for what is "one" thing, then you're giving it up -or better: trading it- for the advantage of hash lookup.

To re-gain the psychological feeling of unity you may make them into a single HoH with keys qw/direct reverse/ associated to the "direct" and "reverse" hashrefs.