[exikyut]

I'd be interested to learn about significantly complex, nontrivial systems of say 100K to 1M LOC scale that require reasoning about every single instruction from the perspective of every other instruction, in order for the system to work.

[benou]

You do not do that. Instead you optimize the short, critical part.

Of course it does not apply to everything, you need a few hotspots, but it is quite common: audio/video codecs, scientific computation, games, crypto... And even networking.

[fit2rule]

And with Lua (and C, and C++) its pretty easy to manage the complexity. Just put things where they belong.