Code Base Analysis

Unfortunately, nearly all languages allow for runtime loading of code and/or reflection which make full static analysis impossible because the code could be used dynamically. Though those tools exist for most languages if you’re willing to live with that caveat - not a few languages/IDEs do this sort of dead code/reference analysis these days and emit warnings.

Full runtime analysis is impossible because it’s equivalent to the halting problem (is that code really dead, or has it just not been called yet?). Though those tools exist if you’re willing to live with that caveat. Depending on your situation, a simple code coverage tool (perhaps in combination with a fuzzer) might be sufficient, which come with many testing frameworks.