Currently, whether a block argument is needed or not, block bodies always process any incoming block. At a minimum, this causes a lot of boolean logic and some field acceses that are not usually necessary. At worst, it creates a Proc object for a given block when it's not needed.

The compiler needs to be modified not to do this. The logic to make the processBlockArgument call is in HeapBasedVariableCompiler and StackBasedVariableCompiler. There's some complications since we don't pass through information on whether the block is present, and all block-compiling logic assumes the block arg value will be pushed onto the stack for arg processing. Needs some retooling to work right.