Reducing boxing and unboxing of Word64 values

Magnus has proposed to eliminate the amount of boxing and unboxing of the Word64 values in the compiler.

It should be possible to reduce the amount of boxing and unboxing happening during compilation on the Word64 values. It would be probably best to do the decision about all the boxing just before forcing the 2-reg code in the Word lang. This would make it possible to eliminate all the unnecessary unboxed values. I think this would provide a better 2-reg code and elimination for WordLang in the end. Any thoughts on why it should probably happen elsewhere in the compiler?