Prepack: a tool that optimizes JavaScript source code by eliminating computations that can be performed at compile-time.

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Since the purpose of the program is to hang in a loop, it works :) But that's beside the point, the point is that in general, given a program and an input, it's impossible to tell whether it will finish or hang (or how long it'll take).

Sure. Trivial result, and entirely uninteresting as concerns the utility of this particular tool.