Remove unused local variables/expressions

[Woccz]

Any local variable or expression that has no effect on a global variable can be removed.

i.e.

• Is never assigned to a global, or recursively to a local which is assigned to a global.
• Is never evaluated:
  • in if
  • in runtime error generator

The first implementation of this could merely remove any locals that are never evaluated, in any context.

Note: Obviously, any competent programmer can remove useless expressions from their code, but with libraries and other code reusability(e.g. #62), this maybe be a helpful optimisation.

Thank you.

[dbaumgarten]

Finding out of a variable somehow influences a global should be possible, but probably requires some effort to do it properly.
Removing assignments to variables that er never referenced would be a good first step.

Given that this will not be used very often and would require relatively much work: backlog