I have tests for subexpressions on the hash, and yes, nested subexpressions causes a lot of duplication. 

Take a look at this gist: https://gist.github.com/machty/2091198e5cba9fe0163f On here I voiced some concerns about duplication, getting rid of stack vars, etc, and Yehuda seemed pretty ok with it given that gzip is a thing. (Though it still startled me at first)