I'd suggest you take a look at perl -w and/or use warnings; - they'll provide a lot of useful information for some (although not all) of what you need, for example warning about variables that are only used once, and (known) calls that can return a zero value that haven't been checked for.

Perldoc has some useful information about using warnings here.

Above and beyond that, I'm not aware of any tool that does what you ask - maybe others can point you in a better direction there.

Hope that helps ..
-- Foxcub