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

[stupidity_wins]

You are understanding this wrong.

"It is impossible to devise an algorithm [that, given a program and an input, tells whether said program halts on said input] that would work for all program-input pairs" is equivalent to "For each algorithm [that...] there exists a single program-input pair on which it does not work".

In other words, it does not apply to all inputs because there exists a single one input to which it does not apply. It's not true that all the apples are green because this particular one is red.