Not really. What happens if you associate the same sub with two keys?

my $code = sub {
  #
  # some sort of magic currently unknown to me
  #
};

$h{'abc','xyz'} = ($code) x 2;
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The only way I can see is if you embed a self-referential closure to the coderef within the sub and then grep the hash looking for a key with that coderef as it's value.

You could probably use someting in the B::* set of modules to walk the optree and locate yourself (you own coderef) from within the sub, but you're still back to searching the hash for keys with that as a value.